diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 4942d99..1e12928 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -160,6 +160,7 @@ jobs:
           cp packaging/proton-drive.service deb/usr/lib/systemd/user/
           cp LICENSE deb/usr/share/licenses/proton-drive-linux/
           po/build.sh deb/usr/share/locale
+          packaging/completions.sh target/release/pdfs deb/usr/share
 
           # Stops the running daemon before removal, so the mount stops mirroring deletes
           install -m755 packaging/deb/prerm deb/DEBIAN/prerm
diff --git a/Cargo.lock b/Cargo.lock
index 0ad8a5f..a8dc170 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -754,6 +754,18 @@ dependencies = [
  "strsim",
 ]
 
+[[package]]
+name = "clap_complete"
+version = "4.6.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "037e2a1a92236d0aff7e845093f64661d6df4c02c9fcc61a60e9e1d736fa392f"
+dependencies = [
+ "clap",
+ "clap_lex",
+ "is_executable",
+ "shlex",
+]
+
 [[package]]
 name = "clap_derive"
 version = "4.6.7"
@@ -2551,6 +2563,15 @@ version = "2.12.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "791930b43c0d5973160d90a8f3894509f2b273430f5c5c73b668636d0287c5c0"
 
+[[package]]
+name = "is_executable"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "82cb6a9f675da968c63b6208c641b9dca58fc0133ae53375736b1767b0cab8bd"
+dependencies = [
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "is_terminal_polyfill"
 version = "1.70.2"
@@ -3524,6 +3545,7 @@ version = "3.7.0"
 dependencies = [
  "anyhow",
  "clap",
+ "clap_complete",
  "pdfs-core",
  "pdfs-fuse",
  "rpassword",
diff --git a/Cargo.toml b/Cargo.toml
index 63cf0d6..bc5cbe1 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -57,6 +57,9 @@ rusqlite = { version = "0.41", features = ["bundled"] }
 keyring-core = "1"
 dbus-secret-service-keyring-store = { version = "1", features = ["crypto-rust"] }
 clap = { version = "4", features = ["derive"] }
+# `unstable-dynamic`: Tab calls `pdfs` back, so arguments complete from the
+# running service. Only `pdfs-cli/src/complete.rs` uses it.
+clap_complete = { version = "4.6", features = ["unstable-dynamic"] }
 rpassword = "7"
 async-trait = "0.1"
 futures = "0.3"
diff --git a/README.md b/README.md
index eecceac..4b0d64d 100644
--- a/README.md
+++ b/README.md
@@ -125,7 +125,7 @@ The documentation is in [`docs/`](docs/README.md) and on the
 | [Getting started](docs/GETTING_STARTED.md) | From installing to your first synced folder |
 | [User guide](docs/USER_GUIDE.md) | Everything the app, tray and launcher do |
 | [FAQ](docs/FAQ.md) | Short answers to common questions |
-| [Command-line reference](docs/CLI.md) | Every `pdfs` command and scripting with `--json` |
+| [Command-line reference](docs/CLI.md) | Every `pdfs` command, Tab completion and scripting with `--json` |
 | [Configuration](docs/CONFIGURATION.md) | `config.json`, file locations, environment variables, the service |
 | [Troubleshooting](docs/TROUBLESHOOTING.md) | Diagnosing problems and fixing common ones |
 | [Recovering on a new computer](docs/RECOVERY.md) | Getting your synced folders back after a reinstall or a lost machine |
diff --git a/crates/pdfs-cli/Cargo.toml b/crates/pdfs-cli/Cargo.toml
index f4a8eba..f4395e6 100644
--- a/crates/pdfs-cli/Cargo.toml
+++ b/crates/pdfs-cli/Cargo.toml
@@ -21,6 +21,7 @@ anyhow.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true
 clap.workspace = true
+clap_complete.workspace = true
 rpassword.workspace = true
 serde_json.workspace = true
 zeroize.workspace = true
diff --git a/crates/pdfs-cli/src/complete.rs b/crates/pdfs-cli/src/complete.rs
new file mode 100644
index 0000000..284ad27
--- /dev/null
+++ b/crates/pdfs-cli/src/complete.rs
@@ -0,0 +1,731 @@
+//! Shell completion for `pdfs`.
+//!
+//! Built on clap_complete's dynamic engine: the script a shell loads is a thin
+//! stub that calls `pdfs` back on every Tab with the words typed so far, and
+//! `pdfs` answers from its own clap definition. That lets an argument complete
+//! from the running service as well as from the command tree — `pdfs sync rm
+//! <Tab>` offers the synced-folder ids with their paths, `pdfs pin Doc<Tab>`
+//! walks My files.
+//!
+//! Every value that comes from the service is best effort. With no service, a
+//! slow one or an error, a completer offers nothing: a Tab that hangs or prints
+//! an error into the prompt is worse than one that does nothing.
+//!
+//! The engine sits behind clap_complete's `unstable-dynamic` feature, so all of
+//! this crate's use of it is kept to this module.
+
+use std::ffi::{OsStr, OsString};
+use std::path::{Path, PathBuf};
+use std::time::Duration;
+
+use clap::CommandFactory;
+use clap_complete::engine::{CompletionCandidate, PathCompleter, ValueCompleter};
+use clap_complete::env::{Bash, CompleteEnv, Elvish, EnvCompleter, Fish, Powershell, Zsh};
+use pdfs_core::control::{
+    AlbumInfo, BookmarkInfo, ConflictInfo, DeviceInfo, DirEntry, InvitationInfo, PendingOpInfo,
+    PublicLinkInfo, Request, Response, RevisionInfo, ShareEntry, ShareEntryKind, SyncFolderInfo,
+};
+
+/// The environment variable that turns a run of `pdfs` into a completion
+/// request. Not clap's generic `COMPLETE`: the same binary is the systemd
+/// daemon, and an unrelated `COMPLETE` in its environment must not stop it.
+pub const VAR: &str = "PDFS_COMPLETE";
+
+/// How long a completer waits for the service. A Tab is interactive, so a
+/// listing the service cannot give soon is better skipped. Long enough for the
+/// listings that ask Proton (computers take over a second).
+const SERVICE_TIMEOUT: Duration = Duration::from_secs(2);
+
+/// How long a listing that asks Proton is reused. Every Tab is a new `pdfs`, so
+/// without it `pdfs devices rm <Tab>`, a letter and another Tab would wait for
+/// Proton twice. A uid that went away in the meantime only fails the command.
+const CACHE_TTL: Duration = Duration::from_secs(30);
+
+/// Answer a completion request and exit, if this run is one. Must run before
+/// anything writes to stdout.
+pub fn handle_request() {
+    CompleteEnv::with_factory(crate::Cli::command)
+        .var(VAR)
+        .complete();
+}
+
+/// The shells `pdfs completions` writes a script for.
+#[derive(Clone, Copy, clap::ValueEnum)]
+pub enum ShellArg {
+    Bash,
+    Zsh,
+    Fish,
+    Elvish,
+    Powershell,
+}
+
+impl ShellArg {
+    fn completer(self) -> &'static dyn EnvCompleter {
+        match self {
+            ShellArg::Bash => &Bash,
+            ShellArg::Zsh => &Zsh,
+            ShellArg::Fish => &Fish,
+            ShellArg::Elvish => &Elvish,
+            ShellArg::Powershell => &Powershell,
+        }
+    }
+}
+
+/// Write the script that registers `pdfs` completion with `shell`.
+///
+/// The script calls `pdfs` from `PATH`, not this binary's path, so one written
+/// at packaging time keeps working once installed.
+pub fn write_script(shell: ShellArg, out: &mut dyn std::io::Write) -> std::io::Result<()> {
+    shell
+        .completer()
+        .write_registration(VAR, "pdfs", "pdfs", "pdfs", out)?;
+    if let ShellArg::Zsh = shell {
+        // Installed as `_pdfs` in site-functions, the script is autoloaded as
+        // that function's body on the first Tab. The body above only defines
+        // and registers the completer, so this line also runs it, or the first
+        // Tab would complete nothing. Sourced, `funcstack` names no `_pdfs`.
+        writeln!(
+            out,
+            "if [ \"$funcstack[1]\" = \"_pdfs\" ]; then\n    _clap_dynamic_completer_pdfs \"$@\"\nfi"
+        )?;
+    }
+    Ok(())
+}
+
+// ---------------------------------------------------------------------------
+// Talking to the service
+
+/// One request to the service, or `None` if there is no answer worth showing.
+fn ask(request: Request) -> Option<Response> {
+    let socket = pdfs_core::config::AppDirs::new().ok()?.control_socket();
+    ask_at(&socket, &request)
+}
+
+fn ask_at(socket: &Path, request: &Request) -> Option<Response> {
+    match pdfs_core::control::send_with_timeout(socket, request, SERVICE_TIMEOUT) {
+        Ok(Response::Error { .. }) | Err(_) => None,
+        Ok(response) => Some(response),
+    }
+}
+
+/// [`ask`] for a listing that comes from Proton rather than the local
+/// database, reusing an answer younger than [`CACHE_TTL`]. `key` names the
+/// listing's cache file.
+fn ask_cached(key: &str, request: Request) -> Option<Response> {
+    let file = cache_file(key);
+    if let Some(hit) = file.as_deref().and_then(read_fresh) {
+        return Some(hit);
+    }
+    let response = ask(request)?;
+    if let Some(file) = &file {
+        write_cache(file, &response);
+    }
+    Some(response)
+}
+
+/// In `$XDG_RUNTIME_DIR`: private to the user, in memory and gone at logout,
+/// which suits names from the account. With no runtime dir, nothing is cached.
+fn cache_file(key: &str) -> Option<PathBuf> {
+    let runtime = PathBuf::from(std::env::var_os("XDG_RUNTIME_DIR")?);
+    Some(
+        runtime
+            .join("proton-drive-linux")
+            .join(format!("completion-{key}.json")),
+    )
+}
+
+fn read_fresh(file: &Path) -> Option<Response> {
+    let age = std::fs::metadata(file)
+        .ok()?
+        .modified()
+        .ok()?
+        .elapsed()
+        .ok()?;
+    if age > CACHE_TTL {
+        return None;
+    }
+    serde_json::from_slice(&std::fs::read(file).ok()?).ok()
+}
+
+/// Best effort: a cache that cannot be written only costs the next Tab a wait.
+fn write_cache(file: &Path, response: &Response) {
+    use std::os::unix::fs::{DirBuilderExt, OpenOptionsExt};
+
+    let (Some(dir), Ok(json)) = (file.parent(), serde_json::to_vec(response)) else {
+        return;
+    };
+    let _ = std::fs::DirBuilder::new()
+        .recursive(true)
+        .mode(0o700)
+        .create(dir);
+    let staging = file.with_extension(format!("{}.tmp", std::process::id()));
+    let written = std::fs::OpenOptions::new()
+        .write(true)
+        .create_new(true)
+        .mode(0o600)
+        .open(&staging)
+        .and_then(|mut f| std::io::Write::write_all(&mut f, &json));
+    if written.is_err() || std::fs::rename(&staging, file).is_err() {
+        let _ = std::fs::remove_file(&staging);
+    }
+}
+
+fn candidate(value: impl Into<OsString>, help: impl Into<String>) -> CompletionCandidate {
+    let help = help.into();
+    let candidate = CompletionCandidate::new(value);
+    if help.is_empty() {
+        candidate
+    } else {
+        candidate.help(Some(help.into()))
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Paths in Proton Drive
+
+/// A path in the mount: an absolute path completes from the local filesystem
+/// (through the mount), anything else from the service's listing of My files,
+/// which is what the commands resolve a relative path against.
+pub fn drive_path(current: &OsStr) -> Vec<CompletionCandidate> {
+    complete_drive(current, false)
+}
+
+/// [`drive_path`] for an argument that must be a folder.
+pub fn drive_dir(current: &OsStr) -> Vec<CompletionCandidate> {
+    complete_drive(current, true)
+}
+
+/// `pdfs refresh`: a folder, or one of the two named caches.
+pub fn refresh_target(current: &OsStr) -> Vec<CompletionCandidate> {
+    let typed = current.to_string_lossy();
+    let mut candidates: Vec<_> = [
+        ("trash", "the trash listing"),
+        ("photos", "the photos timeline"),
+    ]
+    .into_iter()
+    .filter(|(name, _)| name.starts_with(typed.as_ref()))
+    .map(|(name, help)| candidate(name, help))
+    .collect();
+    candidates.extend(drive_dir(current));
+    candidates
+}
+
+fn complete_drive(current: &OsStr, dirs_only: bool) -> Vec<CompletionCandidate> {
+    let Some(word) = current.to_str() else {
+        return Vec::new();
+    };
+    if word.starts_with('/') || word.starts_with('~') {
+        let local = if dirs_only {
+            PathCompleter::dir()
+        } else {
+            PathCompleter::any()
+        };
+        return local.complete(current);
+    }
+    let (parent, prefix) = split_drive_word(word);
+    let listing = Request::ListDir {
+        path: parent.trim_end_matches('/').to_owned(),
+    };
+    match ask(listing) {
+        Some(Response::Entries { entries }) => {
+            drive_candidates(parent, prefix, &entries, dirs_only)
+        }
+        _ => Vec::new(),
+    }
+}
+
+/// Split a typed drive path into the folder to list (with its trailing `/`)
+/// and the start of the name being completed in it.
+fn split_drive_word(word: &str) -> (&str, &str) {
+    match word.rfind('/') {
+        Some(at) => word.split_at(at + 1),
+        None => ("", word),
+    }
+}
+
+/// The entries of `parent` whose name starts with `prefix`. A folder ends in
+/// `/`, which tells every shell not to add a space after it, so the next Tab
+/// goes on into it.
+fn drive_candidates(
+    parent: &str,
+    prefix: &str,
+    entries: &[DirEntry],
+    dirs_only: bool,
+) -> Vec<CompletionCandidate> {
+    entries
+        .iter()
+        .filter(|e| e.name.starts_with(prefix) && (e.is_dir || !dirs_only))
+        .map(|e| {
+            let slash = if e.is_dir { "/" } else { "" };
+            CompletionCandidate::new(format!("{parent}{}{slash}", e.name))
+                .hide(e.name.starts_with('.') && !prefix.starts_with('.'))
+        })
+        .collect()
+}
+
+// ---------------------------------------------------------------------------
+// Ids and uids from the service's listings
+
+pub fn sync_folder_id() -> Vec<CompletionCandidate> {
+    match ask(Request::ListSyncFolders) {
+        Some(Response::SyncFolders { items }) => sync_folder_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn sync_folder_candidates(items: &[SyncFolderInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|f| candidate(f.id.to_string(), format!("{} ({})", f.local_path, f.mode)))
+        .collect()
+}
+
+pub fn queue_id() -> Vec<CompletionCandidate> {
+    match ask(Request::ListPendingOps) {
+        Some(Response::PendingOps { items }) => queue_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn queue_candidates(items: &[PendingOpInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|op| candidate(op.id.to_string(), format!("{} {}", op.kind, op.path)))
+        .collect()
+}
+
+pub fn device_uid() -> Vec<CompletionCandidate> {
+    match ask_cached("devices", Request::ListDevices) {
+        Some(Response::Devices { items }) => device_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn device_candidates(items: &[DeviceInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|d| {
+            let this = if d.this_device {
+                " (this computer)"
+            } else {
+                ""
+            };
+            candidate(d.uid.as_str(), format!("{}{this}", d.name))
+        })
+        .collect()
+}
+
+pub fn trash_uid() -> Vec<CompletionCandidate> {
+    match ask_cached("trash", Request::ListTrash) {
+        Some(Response::Entries { entries }) => trash_candidates(&entries),
+        _ => Vec::new(),
+    }
+}
+
+fn trash_candidates(entries: &[DirEntry]) -> Vec<CompletionCandidate> {
+    entries
+        .iter()
+        .map(|e| {
+            let help = match e.trashed_from.as_deref() {
+                Some(from) if !from.is_empty() => format!("{} (from {from})", e.name),
+                _ => e.name.clone(),
+            };
+            candidate(e.uid.as_str(), help)
+        })
+        .collect()
+}
+
+pub fn album_uid() -> Vec<CompletionCandidate> {
+    match ask_cached("albums", Request::PhotoAlbums) {
+        Some(Response::Albums { items, .. }) => album_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn album_candidates(items: &[AlbumInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|a| candidate(a.uid.as_str(), a.name.as_str()))
+        .collect()
+}
+
+pub fn shared_uid() -> Vec<CompletionCandidate> {
+    match ask_cached("shared-with-me", Request::ListSharedWithMe) {
+        Some(Response::Entries { entries }) => shared_candidates(&entries),
+        _ => Vec::new(),
+    }
+}
+
+fn shared_candidates(entries: &[DirEntry]) -> Vec<CompletionCandidate> {
+    entries
+        .iter()
+        .map(|e| {
+            let help = if e.shared_by.is_empty() {
+                e.name.clone()
+            } else {
+                format!("{} (from {})", e.name, e.shared_by)
+            };
+            candidate(e.uid.as_str(), help)
+        })
+        .collect()
+}
+
+pub fn invitation_id() -> Vec<CompletionCandidate> {
+    match ask_cached("invitations", Request::ListInvitations) {
+        Some(Response::Invitations { items }) => invitation_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn invitation_candidates(items: &[InvitationInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|i| {
+            let help = match i.name.as_deref() {
+                Some(name) => format!("{name} from {}", i.inviter_email),
+                None => format!("from {}", i.inviter_email),
+            };
+            candidate(i.id.as_str(), help)
+        })
+        .collect()
+}
+
+pub fn bookmark_token() -> Vec<CompletionCandidate> {
+    match ask_cached("bookmarks", Request::ListBookmarks) {
+        Some(Response::Bookmarks { items }) => bookmark_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn bookmark_candidates(items: &[BookmarkInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|b| candidate(b.token.as_str(), b.name.as_deref().unwrap_or(&b.url)))
+        .collect()
+}
+
+pub fn conflict_path() -> Vec<CompletionCandidate> {
+    match ask(Request::ListConflicts) {
+        Some(Response::Conflicts { items }) => conflict_candidates(&items),
+        _ => Vec::new(),
+    }
+}
+
+fn conflict_candidates(items: &[ConflictInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|c| candidate(c.path.as_str(), format!("copy of {}", c.original_path)))
+        .collect()
+}
+
+// ---------------------------------------------------------------------------
+// Ids that belong to the path typed before them
+
+/// A version of the file named earlier on the line (`pdfs versions restore
+/// <path> <Tab>`).
+pub fn version_id(current: &OsStr) -> Vec<CompletionCandidate> {
+    let Some(path) = typed_path() else {
+        return Vec::new();
+    };
+    match ask(Request::ListRevisions { path }) {
+        Some(Response::Revisions { items }) => starting_with(current, revision_candidates(&items)),
+        _ => Vec::new(),
+    }
+}
+
+fn revision_candidates(items: &[RevisionInfo]) -> Vec<CompletionCandidate> {
+    items
+        .iter()
+        .map(|r| {
+            let current = if r.is_active { ", current" } else { "" };
+            let size = r.claimed_size.unwrap_or(r.size_on_storage).max(0);
+            candidate(
+                r.id.as_str(),
+                format!(
+                    "{}, {}{current}",
+                    crate::format_epoch_utc(r.created),
+                    crate::human_bytes(size as u64)
+                ),
+            )
+        })
+        .collect()
+}
+
+/// A member or invitation on the share of the path typed earlier on the line.
+pub fn share_entry_id(current: &OsStr) -> Vec<CompletionCandidate> {
+    match share_of_typed_path() {
+        Some((entries, _)) => starting_with(current, share_entry_candidates(&entries)),
+        None => Vec::new(),
+    }
+}
+
+fn share_entry_candidates(entries: &[ShareEntry]) -> Vec<CompletionCandidate> {
+    entries
+        .iter()
+        .map(|e| {
+            // The kind is the next argument, so the help names it in the words
+            // that argument takes.
+            let kind = match e.kind {
+                ShareEntryKind::Member => "member",
+                ShareEntryKind::ProtonInvite => "proton",
+                ShareEntryKind::ExternalInvite => "external",
+            };
+            candidate(e.id.as_str(), format!("{} ({}, {kind})", e.email, e.role))
+        })
+        .collect()
+}
+
+/// The public link of the path typed earlier on the line.
+pub fn public_link_id(current: &OsStr) -> Vec<CompletionCandidate> {
+    match share_of_typed_path() {
+        Some((_, Some(link))) => starting_with(current, vec![public_link_candidate(&link)]),
+        _ => Vec::new(),
+    }
+}
+
+/// Described without its URL: the fragment is the link's password, and a Tab
+/// menu is on screen for anyone watching.
+fn public_link_candidate(link: &PublicLinkInfo) -> CompletionCandidate {
+    let help = match link.expires {
+        Some(expires) => format!(
+            "{} link, expires {}",
+            link.role,
+            crate::format_epoch_utc(expires)
+        ),
+        None => format!("{} link", link.role),
+    };
+    candidate(link.id.as_str(), help)
+}
+
+fn share_of_typed_path() -> Option<(Vec<ShareEntry>, Option<PublicLinkInfo>)> {
+    match ask(Request::ListShare {
+        path: typed_path()?,
+    })? {
+        Response::Share { entries, link } => Some((entries, link)),
+        _ => None,
+    }
+}
+
+/// [`clap_complete::engine::ArgValueCompleter`] candidates are not filtered by
+/// the engine, unlike [`clap_complete::engine::ArgValueCandidates`].
+fn starting_with(
+    current: &OsStr,
+    candidates: Vec<CompletionCandidate>,
+) -> Vec<CompletionCandidate> {
+    let typed = current.to_string_lossy();
+    candidates
+        .into_iter()
+        .filter(|c| c.get_value().to_string_lossy().starts_with(typed.as_ref()))
+        .collect()
+}
+
+/// The `path` argument of the command being completed, as the service takes
+/// it. A completer only receives the word under the cursor, so this reads the
+/// line from the process arguments, where the shell's stub passes it.
+fn typed_path() -> Option<String> {
+    let args: Vec<OsString> = std::env::args_os().collect();
+    let index = std::env::var("_CLAP_COMPLETE_INDEX")
+        .ok()
+        .and_then(|i| i.parse().ok());
+    path_in(words_before_cursor(&args, index))
+}
+
+/// The words of the line before the one being completed. The stub runs
+/// `pdfs -- <words>`; bash, zsh and elvish say which word the cursor is on,
+/// fish and PowerShell pass the line cut at the cursor, so it is the last.
+fn words_before_cursor(args: &[OsString], index: Option<usize>) -> Vec<OsString> {
+    let start = args
+        .iter()
+        .position(|a| a == "--")
+        .map_or(args.len(), |at| at + 1);
+    let mut words = args[start..].to_vec();
+    let index = index.unwrap_or(words.len().saturating_sub(1));
+    words.truncate(index);
+    words
+}
+
+/// Parse `words` as far as they go and take the innermost command's `path`.
+fn path_in(words: Vec<OsString>) -> Option<String> {
+    let matches = crate::Cli::command()
+        .ignore_errors(true)
+        .try_get_matches_from(words)
+        .ok()?;
+    let mut leaf = &matches;
+    while let Some((_, sub)) = leaf.subcommand() {
+        leaf = sub;
+    }
+    let path = leaf.try_get_one::<PathBuf>("path").ok().flatten()?;
+    crate::path_arg(path).ok()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn values(candidates: &[CompletionCandidate]) -> Vec<String> {
+        candidates
+            .iter()
+            .map(|c| c.get_value().to_string_lossy().into_owned())
+            .collect()
+    }
+
+    fn help(candidate: &CompletionCandidate) -> String {
+        candidate
+            .get_help()
+            .map(ToString::to_string)
+            .unwrap_or_default()
+    }
+
+    fn entry(name: &str, is_dir: bool) -> DirEntry {
+        serde_json::from_value(serde_json::json!({
+            "name": name,
+            "is_dir": is_dir,
+            "size": 0,
+            "modified": 0,
+            "pinned": false,
+            "uid": format!("vol~{name}"),
+        }))
+        .unwrap()
+    }
+
+    fn words(line: &[&str]) -> Vec<OsString> {
+        line.iter().map(OsString::from).collect()
+    }
+
+    #[test]
+    fn the_command_definition_is_valid() {
+        crate::Cli::command().debug_assert();
+    }
+
+    #[test]
+    fn completions_script_is_written_for_every_shell() {
+        for shell in [
+            ShellArg::Bash,
+            ShellArg::Zsh,
+            ShellArg::Fish,
+            ShellArg::Elvish,
+            ShellArg::Powershell,
+        ] {
+            let mut script = Vec::new();
+            write_script(shell, &mut script).unwrap();
+            let script = String::from_utf8(script).unwrap();
+            assert!(script.contains(VAR), "{script}");
+            assert!(script.contains("pdfs"), "{script}");
+        }
+    }
+
+    #[test]
+    fn drive_path_splits_parent_and_prefix() {
+        assert_eq!(split_drive_word(""), ("", ""));
+        assert_eq!(split_drive_word("Doc"), ("", "Doc"));
+        assert_eq!(split_drive_word("Documents/"), ("Documents/", ""));
+        assert_eq!(split_drive_word("Documents/Rep"), ("Documents/", "Rep"));
+        assert_eq!(split_drive_word("a/b/c"), ("a/b/", "c"));
+    }
+
+    #[test]
+    fn drive_dirs_end_in_a_slash() {
+        let entries = [
+            entry("Reports", true),
+            entry("Receipt.pdf", false),
+            entry("Other", true),
+        ];
+        let all = drive_candidates("Documents/", "Re", &entries, false);
+        assert_eq!(
+            values(&all),
+            ["Documents/Reports/", "Documents/Receipt.pdf"]
+        );
+        let dirs = drive_candidates("Documents/", "", &entries, true);
+        assert_eq!(values(&dirs), ["Documents/Reports/", "Documents/Other/"]);
+    }
+
+    #[test]
+    fn hidden_drive_entries_need_a_typed_dot() {
+        let entries = [entry(".git", true)];
+        assert!(drive_candidates("", "", &entries, false)[0].is_hide_set());
+        assert!(!drive_candidates("", ".", &entries, false)[0].is_hide_set());
+    }
+
+    #[test]
+    fn sync_folder_ids_complete_with_their_local_path() {
+        let folders: Vec<SyncFolderInfo> = serde_json::from_value(serde_json::json!([{
+            "id": 3,
+            "local_path": "/home/me/Documents",
+            "remote_uid": "vol~docs",
+            "mode": "mirror",
+            "state": "idle",
+            "last_sync": 0,
+        }]))
+        .unwrap();
+        let candidates = sync_folder_candidates(&folders);
+        assert_eq!(values(&candidates), ["3"]);
+        assert_eq!(help(&candidates[0]), "/home/me/Documents (mirror)");
+    }
+
+    #[test]
+    fn trash_uids_complete_with_their_name() {
+        let mut from_docs = entry("a.pdf", false);
+        from_docs.trashed_from = Some("Documents".into());
+        let candidates = trash_candidates(&[from_docs, entry("b", true)]);
+        assert_eq!(values(&candidates), ["vol~a.pdf", "vol~b"]);
+        assert_eq!(help(&candidates[0]), "a.pdf (from Documents)");
+        assert_eq!(help(&candidates[1]), "b");
+    }
+
+    #[test]
+    fn completer_without_a_service_offers_nothing() {
+        let dir = std::env::temp_dir().join(format!("pdfs-complete-{}", std::process::id()));
+        let socket = dir.join("control.sock");
+        assert!(ask_at(&socket, &Request::ListSyncFolders).is_none());
+    }
+
+    #[test]
+    fn cached_listing_is_reused_until_it_is_stale() {
+        let dir = std::env::temp_dir().join(format!("pdfs-complete-cache-{}", std::process::id()));
+        let file = dir.join("completion-devices.json");
+        write_cache(&file, &Response::Devices { items: Vec::new() });
+        assert!(matches!(read_fresh(&file), Some(Response::Devices { .. })));
+        let mode = std::os::unix::fs::PermissionsExt::mode(
+            &std::fs::metadata(&file).unwrap().permissions(),
+        );
+        assert_eq!(mode & 0o777, 0o600);
+
+        let stale = std::time::SystemTime::now() - CACHE_TTL - Duration::from_secs(1);
+        std::fs::File::options()
+            .write(true)
+            .open(&file)
+            .unwrap()
+            .set_modified(stale)
+            .unwrap();
+        assert!(read_fresh(&file).is_none());
+        std::fs::remove_dir_all(dir).unwrap();
+    }
+
+    #[test]
+    fn words_before_cursor_stop_at_the_cursor() {
+        let args = words(&[
+            "pdfs", "--", "pdfs", "versions", "restore", "a.txt", "", "x",
+        ]);
+        assert_eq!(
+            words_before_cursor(&args, Some(4)),
+            words(&["pdfs", "versions", "restore", "a.txt"])
+        );
+        // fish: the line arrives cut at the cursor, the current word last.
+        let fish = words(&["pdfs", "--", "pdfs", "versions", "restore", "a.txt", "ab"]);
+        assert_eq!(
+            words_before_cursor(&fish, None),
+            words(&["pdfs", "versions", "restore", "a.txt"])
+        );
+    }
+
+    #[test]
+    fn completing_words_finds_the_path_before_the_id() {
+        let line = words(&["pdfs", "versions", "restore", "Documents/a.txt"]);
+        assert_eq!(path_in(line).as_deref(), Some("Documents/a.txt"));
+        let line = words(&["pdfs", "--json", "share-role", "Shared/x"]);
+        assert_eq!(path_in(line).as_deref(), Some("Shared/x"));
+        let line = words(&["pdfs", "public-link", "update", "--role", "editor", "a"]);
+        assert_eq!(path_in(line).as_deref(), Some("a"));
+        assert_eq!(path_in(words(&["pdfs", "versions", "restore"])), None);
+    }
+}
diff --git a/crates/pdfs-cli/src/main.rs b/crates/pdfs-cli/src/main.rs
index 3c4c59b..87fb67a 100644
--- a/crates/pdfs-cli/src/main.rs
+++ b/crates/pdfs-cli/src/main.rs
@@ -8,7 +8,8 @@ use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
 use anyhow::{Context, Result, anyhow, bail};
-use clap::{Parser, Subcommand};
+use clap::{Parser, Subcommand, ValueHint};
+use clap_complete::engine::{ArgValueCandidates, ArgValueCompleter};
 use pdfs_core::auth;
 use pdfs_core::cache::ContentCache;
 use pdfs_core::config::AppDirs;
@@ -20,6 +21,7 @@ use pdfs_core::control::{
 use pdfs_core::db::Db;
 use pdfs_core::service;
 
+mod complete;
 mod journal;
 
 /// `println!` for this binary, shadowing std's, which panics when stdout is
@@ -165,6 +167,7 @@ enum Command {
     /// Mount Proton Drive at the given (or default) path. Blocks until unmounted.
     Mount {
         /// Mountpoint; defaults to ~/ProtonDrive.
+        #[arg(value_hint = ValueHint::DirPath)]
         mountpoint: Option<PathBuf>,
     },
     /// Run the auto-mount daemon: wait for login, mount, and keep it mounted
@@ -172,6 +175,7 @@ enum Command {
     /// don't invoke it by hand.
     Daemon {
         /// Mountpoint; defaults to ~/ProtonDrive.
+        #[arg(value_hint = ValueHint::DirPath)]
         mountpoint: Option<PathBuf>,
     },
     /// Keep a file or folder on this device (download + cache it). A folder's
@@ -179,11 +183,13 @@ enum Command {
     /// Needs a running mount.
     Pin {
         /// File or folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
     },
     /// Stop keeping a file or folder on this device, evicting its cached content.
     Unpin {
         /// File or folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
     },
     /// List files and folders pinned to this device.
@@ -191,6 +197,7 @@ enum Command {
     /// List a directory via the running daemon (in-app browser backend).
     Ls {
         /// Directory path, inside the mountpoint or relative to it. Root if omitted.
+        #[arg(add = ArgValueCompleter::new(complete::drive_dir))]
         path: Option<PathBuf>,
     },
     /// List the photos timeline (newest first) via the running daemon.
@@ -224,7 +231,7 @@ enum Command {
     /// so an interrupted import can simply be run again.
     ImportGooglePhotos {
         /// The export's `.zip` files (e.g. `takeout-*.zip`).
-        #[arg(required = true)]
+        #[arg(required = true, value_hint = ValueHint::FilePath)]
         archives: Vec<PathBuf>,
         /// Report what would be imported without uploading anything.
         #[arg(long)]
@@ -277,6 +284,7 @@ enum Command {
     /// List the photos in one album (newest capture first).
     Album {
         /// Album node uid in `volume~link` form (from `pdfs albums`).
+        #[arg(add = ArgValueCandidates::new(complete::album_uid))]
         uid: String,
         /// Max photos to list.
         #[arg(long, default_value_t = 50)]
@@ -293,6 +301,7 @@ enum Command {
     /// Rename a photo album.
     RenameAlbum {
         /// Album node uid in `volume~link` form (from `pdfs albums`).
+        #[arg(add = ArgValueCandidates::new(complete::album_uid))]
         uid: String,
         /// New name.
         name: String,
@@ -300,6 +309,7 @@ enum Command {
     /// Delete a photo album. Its photos stay in the timeline.
     DeleteAlbum {
         /// Album node uid in `volume~link` form (from `pdfs albums`).
+        #[arg(add = ArgValueCandidates::new(complete::album_uid))]
         uid: String,
         /// Also delete photos that exist only in this album (saved from a
         /// shared album); without it the server refuses to delete such an album.
@@ -309,6 +319,7 @@ enum Command {
     /// Add photos to an album.
     AddToAlbum {
         /// Album node uid in `volume~link` form (from `pdfs albums`).
+        #[arg(add = ArgValueCandidates::new(complete::album_uid))]
         uid: String,
         /// Photo node uids (from `pdfs photos`).
         #[arg(required = true)]
@@ -317,6 +328,7 @@ enum Command {
     /// Take photos out of an album. They stay in the timeline.
     RemoveFromAlbum {
         /// Album node uid in `volume~link` form (from `pdfs albums`).
+        #[arg(add = ArgValueCandidates::new(complete::album_uid))]
         uid: String,
         /// Photo node uids (from `pdfs album <uid>`).
         #[arg(required = true)]
@@ -335,13 +347,14 @@ enum Command {
         #[arg(long, default_value_t = 50)]
         limit: usize,
         /// Only search below this folder (under the mountpoint).
-        #[arg(long = "in", value_name = "FOLDER")]
+        #[arg(long = "in", value_name = "FOLDER", add = ArgValueCompleter::new(complete::drive_dir))]
         scope: Option<PathBuf>,
     },
     /// Rename a file or folder via the running daemon.
     Rename {
         /// File/folder path, inside My files or an on-demand synced folder, or
         /// relative to the mountpoint.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// New name (a single path component).
         new_name: String,
@@ -355,7 +368,7 @@ enum Command {
     Move {
         /// Files/folders to move, then the destination folder: each inside a
         /// location, or relative to the mountpoint.
-        #[arg(required = true, num_args = 2.., value_name = "PATH")]
+        #[arg(required = true, num_args = 2.., value_name = "PATH", add = ArgValueCompleter::new(complete::drive_path))]
         paths: Vec<PathBuf>,
     },
     /// Copy files or folders into another folder in My files via the running
@@ -367,7 +380,7 @@ enum Command {
     Copy {
         /// Files/folders to copy, then the destination folder: inside My files,
         /// or relative to the mountpoint.
-        #[arg(required = true, num_args = 2.., value_name = "PATH")]
+        #[arg(required = true, num_args = 2.., value_name = "PATH", add = ArgValueCompleter::new(complete::drive_path))]
         paths: Vec<PathBuf>,
     },
     /// Show how much a folder holds on Proton Drive.
@@ -376,18 +389,21 @@ enum Command {
     /// encrypted bytes on storage and includes items in the trash.
     Du {
         /// Folder path, inside My files or relative to the mountpoint.
+        #[arg(add = ArgValueCompleter::new(complete::drive_dir))]
         path: PathBuf,
     },
     /// Trash a file or folder via the running daemon.
     Rm {
         /// File/folder path, inside My files or an on-demand synced folder, or
         /// relative to the mountpoint.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
     },
     /// Create a folder via the running daemon.
     Mkdir {
         /// Parent folder path, inside My files or an on-demand synced folder,
         /// or relative to the mountpoint.
+        #[arg(add = ArgValueCompleter::new(complete::drive_dir))]
         parent: PathBuf,
         /// New folder name (a single path component).
         name: String,
@@ -397,10 +413,10 @@ enum Command {
     /// background; watch progress with `pdfs transfers`.
     Upload {
         /// Local files and/or folders to upload.
-        #[arg(required = true)]
+        #[arg(required = true, value_hint = ValueHint::AnyPath)]
         sources: Vec<PathBuf>,
         /// Destination folder, inside the mountpoint or relative to it.
-        #[arg(short = 't', long = "to", default_value = ".")]
+        #[arg(short = 't', long = "to", default_value = ".", add = ArgValueCompleter::new(complete::drive_dir))]
         parent: PathBuf,
     },
     /// Show the daemon's in-flight transfers (active uploads/downloads).
@@ -415,13 +431,13 @@ enum Command {
     /// Restore trashed items, by uid, to the folders they were trashed from.
     Restore {
         /// Node uids (`volume~link`), as printed by `pdfs trash`.
-        #[arg(required = true)]
+        #[arg(required = true, add = ArgValueCandidates::new(complete::trash_uid))]
         uids: Vec<String>,
     },
     /// Permanently delete trashed items by uid. This cannot be undone.
     DeleteForever {
         /// Node uids (`volume~link`), as printed by `pdfs trash`.
-        #[arg(required = true)]
+        #[arg(required = true, add = ArgValueCandidates::new(complete::trash_uid))]
         uids: Vec<String>,
     },
     /// Permanently delete everything in the trash. This cannot be undone.
@@ -433,6 +449,7 @@ enum Command {
     Refresh {
         /// What to refresh: a folder path (inside the mountpoint or relative to
         /// it), `trash`, or `photos`. The mount root if omitted.
+        #[arg(add = ArgValueCompleter::new(complete::refresh_target))]
         target: Option<String>,
         /// With `photos`: read every photo's metadata again instead of only what
         /// changed. Minutes on a large library; for a gallery that disagrees with
@@ -459,12 +476,13 @@ enum Command {
     /// Share a file or folder with Proton and/or external email addresses.
     Share {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// One or more invitee emails (Proton or external, auto-detected).
         #[arg(required = true)]
         emails: Vec<String>,
         /// Role to grant: viewer, editor or admin.
-        #[arg(long, default_value = "viewer")]
+        #[arg(long, default_value = "viewer", value_parser = ["viewer", "editor", "admin"], ignore_case = true)]
         role: String,
         /// Optional message included in the invitation email.
         #[arg(long)]
@@ -473,17 +491,21 @@ enum Command {
     /// List a node's members, pending invitations and public link.
     Members {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
     },
     /// Change the role of a member or pending invitation on a node's share.
     ShareRole {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Entry id (membership or invitation id), from `pdfs members`.
+        #[arg(add = ArgValueCompleter::new(complete::share_entry_id))]
         id: String,
         /// Entry kind: member, proton or external.
         kind: ShareKindArg,
         /// New role: viewer, editor or admin.
+        #[arg(value_parser = ["viewer", "editor", "admin"], ignore_case = true)]
         role: String,
     },
     /// Stop sharing a node, or remove one member or pending invitation.
@@ -492,9 +514,10 @@ enum Command {
     /// member. With an id and kind (from `pdfs members`), removes that entry.
     Unshare {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Entry id (membership or invitation id), from `pdfs members`.
-        #[arg(requires = "kind")]
+        #[arg(requires = "kind", add = ArgValueCompleter::new(complete::share_entry_id))]
         id: Option<String>,
         /// Entry kind: member, proton or external.
         kind: Option<ShareKindArg>,
@@ -515,18 +538,22 @@ enum Command {
     SharedWithMe {
         /// Folder uid to list into, in `volume~link` form (from a previous run).
         /// Omit for the top level.
+        #[arg(add = ArgValueCandidates::new(complete::shared_uid))]
         uid: Option<String>,
     },
     /// Download a file shared with me by its uid (from `pdfs shared-with-me`).
     SharedGet {
         /// Node uid in `volume~link` form.
+        #[arg(add = ArgValueCandidates::new(complete::shared_uid))]
         uid: String,
         /// Where to write it. Omit to leave it in the cache and print the path.
+        #[arg(value_hint = ValueHint::AnyPath)]
         dest: Option<PathBuf>,
     },
     /// Leave a shared node by its uid (from `pdfs shared-with-me`).
     Leave {
         /// Node uid in `volume~link` form.
+        #[arg(add = ArgValueCandidates::new(complete::shared_uid))]
         uid: String,
     },
     /// Manage invitations addressed to me.
@@ -557,6 +584,17 @@ enum Command {
     /// Runs without a daemon on purpose: the state worth diagnosing is usually
     /// the state where the daemon will not start.
     Diagnose,
+    /// Print the shell completion script for bash, zsh, fish, elvish or
+    /// PowerShell.
+    ///
+    /// Besides commands and options, it completes values from the running
+    /// service: paths in My files, synced-folder and queue ids, computers,
+    /// trash, albums, shares and versions. Load it with, for example,
+    /// `pdfs completions fish | source` or `source <(pdfs completions bash)`.
+    Completions {
+        /// The shell to write the script for.
+        shell: complete::ShellArg,
+    },
 }
 
 #[derive(Subcommand)]
@@ -604,6 +642,7 @@ enum VersionCmd {
     /// List a file's versions, newest first.
     List {
         /// File path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
     },
     /// Make an earlier version the file's current content.
@@ -612,25 +651,32 @@ enum VersionCmd {
     /// moment to show up in the mount.
     Restore {
         /// File path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Version id, from `pdfs versions list`.
+        #[arg(add = ArgValueCompleter::new(complete::version_id))]
         id: String,
     },
     /// Write an earlier version to a local file, leaving the file untouched.
     Save {
         /// File path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Version id, from `pdfs versions list`.
+        #[arg(add = ArgValueCompleter::new(complete::version_id))]
         id: String,
         /// Where to write it. Must not already exist.
+        #[arg(value_hint = ValueHint::AnyPath)]
         dest: PathBuf,
     },
     /// Permanently delete an earlier version. The content is unrecoverable, and
     /// the version that is currently active cannot be deleted.
     Rm {
         /// File path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Version id, from `pdfs versions list`.
+        #[arg(add = ArgValueCompleter::new(complete::version_id))]
         id: String,
     },
 }
@@ -640,13 +686,21 @@ enum DeviceCmd {
     /// List registered devices.
     List,
     /// Rename a device by uid.
-    Rename { uid: String, name: String },
+    Rename {
+        #[arg(add = ArgValueCandidates::new(complete::device_uid))]
+        uid: String,
+        name: String,
+    },
     /// Delete (deregister) a device by uid.
-    Rm { uid: String },
+    Rm {
+        #[arg(add = ArgValueCandidates::new(complete::device_uid))]
+        uid: String,
+    },
     /// Adopt an existing device as this machine's, so a hostname change or a
     /// reinstall re-attaches to it instead of registering a duplicate.
     Adopt {
         /// Device uid (from `devices list`). Omit with `--clear`.
+        #[arg(add = ArgValueCandidates::new(complete::device_uid))]
         uid: Option<String>,
         /// Drop the adoption and go back to matching by hostname.
         #[arg(long, conflicts_with = "uid")]
@@ -657,6 +711,7 @@ enum DeviceCmd {
     /// here. Both computers keep them in step.
     Join {
         /// Device uid (from `devices list`).
+        #[arg(add = ArgValueCandidates::new(complete::device_uid))]
         uid: String,
         /// Skip the confirmation and accept every proposed local path.
         #[arg(long)]
@@ -666,6 +721,7 @@ enum DeviceCmd {
     /// them here. The other computer stays registered, without those folders.
     Migrate {
         /// Device uid (from `devices list`).
+        #[arg(add = ArgValueCandidates::new(complete::device_uid))]
         uid: String,
         /// Skip the confirmation and accept every proposed local path.
         #[arg(long)]
@@ -678,6 +734,7 @@ enum ConflictCmd {
     /// Decide which side of a conflict to keep. Whatever is removed goes to Trash.
     Resolve {
         /// The conflict copy, absolute or relative to the mountpoint.
+        #[arg(add = ArgValueCandidates::new(complete::conflict_path))]
         path: PathBuf,
         /// `original` trashes the copy; `copy` trashes the original and gives the
         /// copy its name; `both` renames the copy to `--name`.
@@ -694,15 +751,17 @@ enum SyncCmd {
     /// Add a local folder to this machine's device and upload its contents.
     Add {
         /// Local directory to sync.
+        #[arg(value_hint = ValueHint::DirPath)]
         path: PathBuf,
     },
     /// Sync a real local folder with an existing folder in My files.
     /// The first pass preserves local-only files and keeps differing versions.
     Attach {
         /// Existing local directory; it remains a real local directory.
+        #[arg(value_hint = ValueHint::DirPath)]
         path: PathBuf,
         /// Existing folder in My files, relative to the cloud mount or inside it.
-        #[arg(long)]
+        #[arg(long, add = ArgValueCompleter::new(complete::drive_dir))]
         to: PathBuf,
     },
     /// List this machine's synced folders.
@@ -710,6 +769,7 @@ enum SyncCmd {
     /// Remove a synced folder by id.
     Rm {
         /// Synced-folder id (from `sync list`).
+        #[arg(add = ArgValueCandidates::new(complete::sync_folder_id))]
         id: i64,
         /// Also delete the folder's copy in Proton Drive.
         #[arg(long)]
@@ -718,6 +778,7 @@ enum SyncCmd {
     /// Force a sync pass now (all folders, or one by id).
     Now {
         /// Optional synced-folder id; omit to reconcile every folder.
+        #[arg(add = ArgValueCandidates::new(complete::sync_folder_id))]
         id: Option<i64>,
     },
     /// Forget what a synced folder synced before and compare it with Proton
@@ -725,6 +786,7 @@ enum SyncCmd {
     /// that differs keeps both versions. Nothing is deleted.
     Reset {
         /// Synced-folder id (from `sync list`).
+        #[arg(add = ArgValueCandidates::new(complete::sync_folder_id))]
         id: i64,
     },
     /// Pause syncing: queued uploads and mirror folders wait, reads keep working.
@@ -734,13 +796,13 @@ enum SyncCmd {
         #[arg(long = "for", value_parser = parse_pause_duration, conflicts_with = "folder")]
         duration: Option<u64>,
         /// Pause only this mirror folder (id from `sync list`) until resumed.
-        #[arg(long)]
+        #[arg(long, add = ArgValueCandidates::new(complete::sync_folder_id))]
         folder: Option<i64>,
     },
     /// Resume syncing after `pdfs sync pause`.
     Resume {
         /// Resume only this folder, paused with `sync pause --folder`.
-        #[arg(long)]
+        #[arg(long, add = ArgValueCandidates::new(complete::sync_folder_id))]
         folder: Option<i64>,
     },
     /// Cap upload and download speed, or show the caps with no options.
@@ -759,8 +821,10 @@ enum SyncCmd {
     /// Save the content of a queued upload (by id from `sync queue`) to a file.
     Export {
         /// Queue id.
+        #[arg(add = ArgValueCandidates::new(complete::queue_id))]
         id: i64,
         /// Where to save it: a new file, or an existing folder to save it in.
+        #[arg(value_hint = ValueHint::AnyPath)]
         dest: PathBuf,
     },
     /// Drop a queued change (by id from `sync queue`) and undo it here: a new file
@@ -768,6 +832,7 @@ enum SyncCmd {
     /// content is lost unless saved with `sync export` first.
     Discard {
         /// Queue id.
+        #[arg(add = ArgValueCandidates::new(complete::queue_id))]
         id: i64,
         /// Do not ask first.
         #[arg(long)]
@@ -776,11 +841,13 @@ enum SyncCmd {
     /// Retry a queued operation now (by id from `sync queue`), or every failed one.
     Retry {
         /// Queue id; omit to retry every failed operation.
+        #[arg(add = ArgValueCandidates::new(complete::queue_id))]
         id: Option<i64>,
     },
     /// Switch a folder between full-copy sync and on-demand (FUSE, no local storage).
     Mode {
         /// Synced-folder id (from `sync list`).
+        #[arg(add = ArgValueCandidates::new(complete::sync_folder_id))]
         id: i64,
         /// `mirror` (full local copy) or `ondemand` (FUSE mount, reclaims disk).
         #[arg(value_parser = ["mirror", "ondemand"])]
@@ -794,7 +861,7 @@ enum SyncCmd {
         yes: bool,
         /// Restore another computer's folders instead, by device uid (from
         /// `pdfs devices list`).
-        #[arg(long)]
+        #[arg(long, add = ArgValueCandidates::new(complete::device_uid))]
         device: Option<String>,
     },
 }
@@ -804,9 +871,10 @@ enum PublicLinkCmd {
     /// Create a public link on a node.
     Create {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Role: viewer or editor.
-        #[arg(long, default_value = "viewer")]
+        #[arg(long, default_value = "viewer", value_parser = ["viewer", "editor"], ignore_case = true)]
         role: String,
         /// Optional custom password protecting the link.
         #[arg(long)]
@@ -819,11 +887,13 @@ enum PublicLinkCmd {
     /// given is kept.
     Update {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Public-link id, from `pdfs members`.
+        #[arg(add = ArgValueCompleter::new(complete::public_link_id))]
         id: String,
         /// New role: viewer or editor.
-        #[arg(long)]
+        #[arg(long, value_parser = ["viewer", "editor"], ignore_case = true)]
         role: Option<String>,
         /// New custom password protecting the link.
         #[arg(long, conflicts_with = "no_password")]
@@ -841,8 +911,10 @@ enum PublicLinkCmd {
     /// Remove a node's public link.
     Remove {
         /// File/folder path, inside the mountpoint or relative to it.
+        #[arg(add = ArgValueCompleter::new(complete::drive_path))]
         path: PathBuf,
         /// Public-link id, from `pdfs members`.
+        #[arg(add = ArgValueCompleter::new(complete::public_link_id))]
         id: String,
     },
 }
@@ -852,9 +924,15 @@ enum InvitationCmd {
     /// List invitations addressed to me.
     List,
     /// Accept an invitation by id.
-    Accept { id: String },
+    Accept {
+        #[arg(add = ArgValueCandidates::new(complete::invitation_id))]
+        id: String,
+    },
     /// Reject an invitation by id.
-    Reject { id: String },
+    Reject {
+        #[arg(add = ArgValueCandidates::new(complete::invitation_id))]
+        id: String,
+    },
 }
 
 #[derive(Subcommand)]
@@ -870,7 +948,10 @@ enum BookmarkCmd {
         password: Option<String>,
     },
     /// Remove a saved bookmark by its token.
-    Rm { token: String },
+    Rm {
+        #[arg(add = ArgValueCandidates::new(complete::bookmark_token))]
+        token: String,
+    },
 }
 
 /// Render a daemon failure for a terminal.
@@ -890,6 +971,9 @@ fn cli_error(kind: ErrorKind, message: &str) -> String {
 }
 
 fn main() -> Result<()> {
+    // First: a completion request answers on stdout and exits, so nothing may
+    // write there before it.
+    complete::handle_request();
     let filter = tracing_subscriber::EnvFilter::try_from_default_env()
         // `pgp` logs a benign WARN when it re-serializes a Proton secret-key
         // packet with a longer (but equivalent) length encoding than the
@@ -1030,6 +1114,7 @@ fn main() -> Result<()> {
         Command::Activity { limit } => cmd_activity(limit),
         Command::Quota => cmd_quota(),
         Command::Cache { action } => cmd_cache(action),
+        Command::Completions { shell } => cmd_completions(shell),
         Command::Diagnose => cmd_diagnose(),
     }
 }
@@ -3806,6 +3891,15 @@ fn writable_probe(dir: &Path) -> std::io::Result<()> {
     result.and(remove)
 }
 
+/// Print the completion script for `shell`. Touches no account state, so
+/// packaging can run it at build time.
+fn cmd_completions(shell: complete::ShellArg) -> Result<()> {
+    let mut script = Vec::new();
+    complete::write_script(shell, &mut script)?;
+    print!("{}", String::from_utf8_lossy(&script));
+    Ok(())
+}
+
 /// Self-check the installation, reporting each finding and exiting non-zero if
 /// any check failed.
 ///
diff --git a/crates/pdfs-core/src/control.rs b/crates/pdfs-core/src/control.rs
index b0dc401..14a37db 100644
--- a/crates/pdfs-core/src/control.rs
+++ b/crates/pdfs-core/src/control.rs
@@ -2405,9 +2405,17 @@ impl Request {
 ///
 /// Shared by the CLI and GUI so both speak the wire format identically.
 pub fn send(socket: &Path, req: &Request) -> Result<Response> {
+    send_with_timeout(socket, req, req.read_timeout())
+}
+
+/// [`send`] with a caller-chosen limit on how long the daemon may take to
+/// answer, which also bounds the write. For a caller that must never keep a
+/// person waiting, such as shell completion, where a slow answer is worth less
+/// than none.
+pub fn send_with_timeout(socket: &Path, req: &Request, timeout: Duration) -> Result<Response> {
     let mut stream = UnixStream::connect(socket)?;
-    stream.set_read_timeout(Some(req.read_timeout()))?;
-    stream.set_write_timeout(Some(WRITE_TIMEOUT))?;
+    stream.set_read_timeout(Some(timeout))?;
+    stream.set_write_timeout(Some(timeout.min(WRITE_TIMEOUT)))?;
     let mut line = serde_json::to_vec(req)?;
     line.push(b'\n');
     stream.write_all(&line)?;
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 38f8e4b..9d3637e 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -22,6 +22,12 @@ Existing folders remain device backups; older builds cannot open the upgraded da
 
 ### Added
 
+- Shell completion for `pdfs` in bash, zsh and fish, installed by every package, plus elvish
+  and PowerShell through `pdfs completions SHELL`. Besides commands and options it completes
+  paths in My files and the ids and uids the running service knows (synced folders, the queue,
+  computers, trash, albums, shares, invitations, bookmarks, conflicts and versions), each with
+  a description. Share roles are now checked by the CLI (`viewer`, `editor`, `admin`) before
+  the request.
 - `pdfs sync attach PATH --to REMOTE` connects an existing local directory to an existing
   My files folder. The first sync preserves one-sided files and differing versions (#67).
   Attachments stay in mirror mode, are excluded from device profiles, and cannot delete
diff --git a/docs/CLI.md b/docs/CLI.md
index 2ff6c3d..df95563 100644
--- a/docs/CLI.md
+++ b/docs/CLI.md
@@ -8,6 +8,7 @@ talks to the running service (`proton-drive.service`); `login`, `logout`, `mount
 what the commands do in the app, see the [user guide](USER_GUIDE.md).
 
 - [Conventions](#conventions)
+- [Shell completion](#shell-completion)
 - [Account and service](#account-and-service)
 - [Files](#files)
 - [Available offline](#available-offline)
@@ -32,6 +33,36 @@ what the commands do in the app, see the [user guide](USER_GUIDE.md).
   service.
 - **Output** is English and stable enough for `grep`; use `--json` where it is available.
 
+## Shell completion
+
+Tab completes commands and options, and also the values the service knows. Paths complete
+from My files, and these complete with a description: synced-folder and queue ids, computers,
+trash items, albums, items shared with you, invitations, bookmarks, conflict copies, and a file's
+versions or a share's members and link once the path is typed. Values come from the running
+service. Without it, only commands, options and local paths complete.
+
+| Example | Completes |
+|---|---|
+| `pdfs pin Doc<Tab>` | `Documents/`; Tab again lists its contents |
+| `pdfs sync rm <Tab>` | `1  /home/me/Documents (mirror)` … |
+| `pdfs devices rm <Tab>` | computer uids, with their names |
+| `pdfs versions restore Documents/a.pdf <Tab>` | version ids, with date and size |
+
+The packages install completion for bash, zsh and fish, which these shells load by themselves. For
+a source build, or another shell, load the script that `pdfs completions <shell>` prints:
+
+| Shell | Add to |
+|---|---|
+| bash | `~/.bashrc`: `source <(pdfs completions bash)` |
+| zsh | `~/.zshrc`, after `compinit`: `source <(pdfs completions zsh)` |
+| fish | `~/.config/fish/config.fish`: `pdfs completions fish \| source` |
+| elvish | `~/.config/elvish/rc.elv`: `eval (pdfs completions elvish \| slurp)` |
+| PowerShell | `$PROFILE`: `pdfs completions powershell \| Out-String \| Invoke-Expression` |
+
+The script runs `pdfs` from `PATH` on every Tab, so it keeps working after an update. A
+`pdfs` that is not on `PATH` prints a script for its own location with
+`PDFS_COMPLETE=<shell> ./pdfs`.
+
 ## Account and service
 
 | Command | Description |
@@ -185,6 +216,7 @@ commands are for scripts and for cases where the mount is not available.
 | `pdfs cache inspect [--deep]` | Database size, reclaimable space, row counts, cache use against the limit. `--deep` also runs SQLite's integrity check (slow). |
 | `pdfs cache vacuum` | Compact the database. Needs free space for a second copy of it while it runs. |
 | `pdfs cache clear` | Delete cached file content. Files kept available offline stay. |
+| `pdfs completions SHELL` | Print the [shell completion](#shell-completion) script for bash, zsh, fish, elvish or powershell. |
 
 [Troubleshooting](TROUBLESHOOTING.md) explains when to use each of these.
 
diff --git a/packaging/PKGBUILD b/packaging/PKGBUILD
index fe35901..d36f144 100644
--- a/packaging/PKGBUILD
+++ b/packaging/PKGBUILD
@@ -80,5 +80,8 @@ package() {
   # Translations: compiled from po/ into /usr/share/locale.
   po/build.sh "$pkgdir/usr/share/locale"
 
+  # Shell completion for bash, zsh and fish.
+  packaging/completions.sh "$rel/pdfs" "$pkgdir/usr/share"
+
   install -Dm644 "LICENSE" "$pkgdir/usr/share/licenses/$pkgname/LICENSE"
 }
diff --git a/packaging/aur/proton-drive-for-linux-bin/PKGBUILD b/packaging/aur/proton-drive-for-linux-bin/PKGBUILD
index 8ed7323..a261940 100644
--- a/packaging/aur/proton-drive-for-linux-bin/PKGBUILD
+++ b/packaging/aur/proton-drive-for-linux-bin/PKGBUILD
@@ -64,6 +64,14 @@ package() {
   install -dm755 "$pkgdir/usr/share"
   cp -r --no-preserve=ownership "$srcdir/locale" "$pkgdir/usr/share/locale"
 
+  # Shell completion for bash, zsh and fish, written by the binary itself.
+  local share="$pkgdir/usr/share"
+  install -d "$share/bash-completion/completions" "$share/zsh/site-functions" \
+    "$share/fish/vendor_completions.d"
+  "$srcdir/pdfs" completions bash > "$share/bash-completion/completions/pdfs"
+  "$srcdir/pdfs" completions zsh > "$share/zsh/site-functions/_pdfs"
+  "$srcdir/pdfs" completions fish > "$share/fish/vendor_completions.d/pdfs.fish"
+
   install -Dm644 "$srcdir/LICENSE-$pkgver" "$pkgdir/usr/share/licenses/$pkgname/LICENSE"
 
   # pacman brings new releases, so the app never checks for them itself.
diff --git a/packaging/aur/proton-drive-for-linux-git/PKGBUILD b/packaging/aur/proton-drive-for-linux-git/PKGBUILD
index 36449f3..f839827 100644
--- a/packaging/aur/proton-drive-for-linux-git/PKGBUILD
+++ b/packaging/aur/proton-drive-for-linux-git/PKGBUILD
@@ -81,6 +81,9 @@ package() {
   # Translations: compiled from po/ into /usr/share/locale.
   po/build.sh "$pkgdir/usr/share/locale"
 
+  # Shell completion for bash, zsh and fish.
+  packaging/completions.sh target/release/pdfs "$pkgdir/usr/share"
+
   install -Dm644 LICENSE "$pkgdir/usr/share/licenses/$pkgname/LICENSE"
   install -Dm644 README.md "$pkgdir/usr/share/doc/$pkgname/README.md"
 
diff --git a/packaging/aur/proton-drive-for-linux/PKGBUILD b/packaging/aur/proton-drive-for-linux/PKGBUILD
index c4e73b6..629d2ab 100644
--- a/packaging/aur/proton-drive-for-linux/PKGBUILD
+++ b/packaging/aur/proton-drive-for-linux/PKGBUILD
@@ -76,6 +76,9 @@ package() {
   # Translations: compiled from po/ into /usr/share/locale.
   po/build.sh "$pkgdir/usr/share/locale"
 
+  # Shell completion for bash, zsh and fish.
+  packaging/completions.sh target/release/pdfs "$pkgdir/usr/share"
+
   install -Dm644 LICENSE "$pkgdir/usr/share/licenses/$pkgname/LICENSE"
   install -Dm644 README.md "$pkgdir/usr/share/doc/$pkgname/README.md"
 
diff --git a/packaging/completions.sh b/packaging/completions.sh
new file mode 100755
index 0000000..de3060b
--- /dev/null
+++ b/packaging/completions.sh
@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+# Write the shell completion scripts of a built `pdfs` into <datadir>, where
+# bash-completion, zsh and fish look for them. Packages pass their install
+# tree, e.g. "$pkgdir/usr/share". The scripts call `pdfs` from PATH on every
+# Tab, so they are the same for every version and need no rebuild per release.
+set -euo pipefail
+
+if [ $# -ne 2 ]; then
+  echo "usage: $0 <pdfs binary> <datadir>" >&2
+  exit 2
+fi
+pdfs="$1"
+datadir="$2"
+
+install -d "$datadir/bash-completion/completions" \
+  "$datadir/zsh/site-functions" \
+  "$datadir/fish/vendor_completions.d"
+"$pdfs" completions bash > "$datadir/bash-completion/completions/pdfs"
+"$pdfs" completions zsh > "$datadir/zsh/site-functions/_pdfs"
+"$pdfs" completions fish > "$datadir/fish/vendor_completions.d/pdfs.fish"
+chmod 644 "$datadir/bash-completion/completions/pdfs" \
+  "$datadir/zsh/site-functions/_pdfs" \
+  "$datadir/fish/vendor_completions.d/pdfs.fish"
diff --git a/packaging/nix/package.nix b/packaging/nix/package.nix
index 3c052b2..c2bce34 100644
--- a/packaging/nix/package.nix
+++ b/packaging/nix/package.nix
@@ -40,6 +40,7 @@ rustPlatform.buildRustPackage {
       ../io.narl.proton-drive-linux.desktop
       ../io.narl.proton-drive-linux-tray.desktop
       ../io.narl.proton-drive-linux.svg
+      ../completions.sh
     ];
   };
 
@@ -107,6 +108,9 @@ rustPlatform.buildRustPackage {
     patchShebangs po/build.sh
     po/build.sh $out/share/locale
 
+    patchShebangs packaging/completions.sh
+    packaging/completions.sh $out/bin/pdfs $out/share
+
     # Nix brings new releases, so the app never checks for them itself.
     install -Dm644 /dev/null $out/share/proton-drive-linux/managed-updates
   '';
diff --git a/packaging/proton-drive-linux.spec b/packaging/proton-drive-linux.spec
index a4c1005..cda09e1 100644
--- a/packaging/proton-drive-linux.spec
+++ b/packaging/proton-drive-linux.spec
@@ -114,6 +114,7 @@ install -D -m0644 %{src}/packaging/io.narl.proton-drive-linux.svg \
 install -D -m0644 %{src}/packaging/proton-drive.service \
   %{buildroot}/usr/lib/systemd/user/proton-drive.service
 %{src}/po/build.sh %{buildroot}%{_datadir}/locale
+%{src}/packaging/completions.sh "$rel/pdfs" %{buildroot}%{_datadir}
 %if 0%{!?git_dir:1}
 # dnf brings new releases from COPR, so the app does not offer its own check.
 install -D -m0644 /dev/null %{buildroot}%{_datadir}/proton-drive-linux/managed-updates
@@ -149,6 +150,9 @@ fi
 %{_datadir}/icons/hicolor/scalable/apps/io.narl.proton-drive-linux.svg
 /usr/lib/systemd/user/proton-drive.service
 %{_datadir}/locale/*/LC_MESSAGES/pdfs.mo
+%{_datadir}/bash-completion/completions/pdfs
+%{_datadir}/zsh/site-functions/_pdfs
+%{_datadir}/fish/vendor_completions.d/pdfs.fish
 %if 0%{!?git_dir:1}
 %{_datadir}/proton-drive-linux/managed-updates
 %endif