diff --git a/docs/wiki/Commands.md b/docs/wiki/Commands.md
index 75bb9ce..d2171a8 100644
--- a/docs/wiki/Commands.md
+++ b/docs/wiki/Commands.md
@@ -60,7 +60,7 @@ arguments and `↑` / `↓` recall earlier lines.
 | `gb` | the documents that link to the open one — \[\[title]] links by title, \[\[ completes one while writing |
 | `:` | command line — Tab / Shift-Tab cycle the matches, then the argument; ↑ ↓ recall what ran before |
 | `Ctrl-S` | save, from anywhere |
-| `?` | this screen — in the editor too |
+| `?` | this screen, from the editor too — h/l a column, / filters it down |
 
 ### On a board
 
diff --git a/docs/wiki/Getting-Started.md b/docs/wiki/Getting-Started.md
index d90e368..0e1e031 100644
--- a/docs/wiki/Getting-Started.md
+++ b/docs/wiki/Getting-Started.md
@@ -74,7 +74,7 @@ The rail of buttons on the right does the same as the keys, for a mouse.
    inbox of this space's board. Press `b` to see the board, and `b` again to go
    back.
 7. Press `T`. That is today's diary entry, started for you.
-8. Press `?` for the list of every key and command, and `Esc` to close it.
+8. Press `?` for the list of every key and command. `h` / `l` walk its columns, `/` narrows it down, and `Esc` closes it.
 
 On a phone the same things are buttons: the dock at the bottom has a new
 document, a new folder, the board, today's entry, an upload and a search, and
diff --git a/web/src/App.svelte b/web/src/App.svelte
index f2f66bb..686496d 100644
--- a/web/src/App.svelte
+++ b/web/src/App.svelte
@@ -9,7 +9,7 @@
   import DocumentPane from './lib/DocumentPane.svelte'
   import FilePane from './lib/FilePane.svelte'
   import Headings from './lib/Headings.svelte'
-  import Help from './lib/Help.svelte'
+  import Help, { focusHelpFilter, scrollHelp } from './lib/Help.svelte'
   import Hints from './lib/Hints.svelte'
   import Verify from './lib/Verify.svelte'
   import Login from './lib/Login.svelte'
@@ -378,6 +378,46 @@
     }
   }
 
+  /**
+   * The help's keys: its columns run on to the right, so h/l and j/k move a
+   * column, Ctrl-D/U a screen, g/G to either end, and `/` narrows it down.
+   */
+  function helpKey(event: KeyboardEvent): boolean {
+    if (event.ctrlKey) {
+      if (event.key !== 'd' && event.key !== 'u') return false
+      scrollHelp(event.key === 'd' ? 'pagedown' : 'pageup')
+      return true
+    }
+    switch (event.key) {
+      case 'l':
+      case 'j':
+      case 'ArrowRight':
+      case 'ArrowDown':
+        scrollHelp(1)
+        return true
+      case 'h':
+      case 'k':
+      case 'ArrowLeft':
+      case 'ArrowUp':
+        scrollHelp(-1)
+        return true
+      case ' ':
+        scrollHelp(event.shiftKey ? 'pageup' : 'pagedown')
+        return true
+      case 'g':
+        scrollHelp('start')
+        return true
+      case 'G':
+        scrollHelp('end')
+        return true
+      case '/':
+        focusHelpFilter()
+        return true
+      default:
+        return false
+    }
+  }
+
   /** `gO`'s list: j/k down the headings, Enter to the one picked. */
   function outlineKey(event: KeyboardEvent): boolean {
     const last = Math.max(workspace.outline.length - 1, 0)
@@ -682,6 +722,12 @@
 
     // The command line over an overlay — `D` in the agenda — keeps its keys.
     const listening = cmdline === null && !isTypingTarget(event.target)
+    if (workspace.overlay === 'help' && listening && !event.metaKey && !event.altKey) {
+      if (helpKey(event)) {
+        event.preventDefault()
+        return
+      }
+    }
     if (workspace.overlay === 'overview' && listening && !event.ctrlKey && !event.metaKey && !event.altKey) {
       if (overviewKey(event)) {
         event.preventDefault()
diff --git a/web/src/lib/Help.svelte b/web/src/lib/Help.svelte
index 21b449b..2a57dc1 100644
--- a/web/src/lib/Help.svelte
+++ b/web/src/lib/Help.svelte
@@ -1,6 +1,47 @@
+<script lang="ts" module>
+  /*
+   * The help is a sheet the size of the porthole, laid out in newspaper
+   * columns that run on to the right, so all of it is in view at once on a
+   * wide screen and a key away on a narrow one. Its keys live in App.svelte
+   * with the others; these are what they move.
+   */
+  let pages: HTMLElement | undefined = $state()
+  let field: HTMLInputElement | undefined = $state()
+  /** `/` in the help: only the rows whose key or words hold this. */
+  export const helpFilter = $state({ text: '' })
+
+  /** A column on or back, a screen on or back, or to either end. */
+  export function scrollHelp(by: 1 | -1 | 'pagedown' | 'pageup' | 'start' | 'end') {
+    if (!pages) return
+    // Columns that run off the right edge scroll sideways; on a phone they
+    // stack, and the sheet around them scrolls down instead.
+    const sideways = pages.scrollWidth > pages.clientWidth
+    const scroller = sideways ? pages : pages.parentElement
+    if (!scroller) return
+    const axis = sideways ? 'left' : 'top'
+    if (by === 'start' || by === 'end') {
+      scroller.scrollTo({ [axis]: by === 'start' ? 0 : 1e9, behavior: 'smooth' })
+      return
+    }
+    const page = sideways ? scroller.clientWidth : scroller.clientHeight
+    // A row is never broken over columns, so it is as wide as one of them.
+    const column = sideways ? (pages.querySelector<HTMLElement>('.row')?.offsetWidth ?? 0) + COLUMN_GAP : page / 2
+    const distance = typeof by === 'number' ? by * column : (by === 'pagedown' ? 1 : -1) * page
+    scroller.scrollBy({ [axis]: distance, behavior: 'smooth' })
+  }
+
+  export function focusHelpFilter() {
+    field?.focus()
+    field?.select()
+  }
+
+  const COLUMN_GAP = 28
+</script>
+
 <script lang="ts">
   import { commands, groups, type CommandSpec, type Group } from './commands'
   import { workspace } from './store.svelte'
+  import { isTouchDevice } from './util'
 
   const keys: [string, string][] = [
     ['1 … 9 · 0', 'switch to that space, like a workspace'],
@@ -50,7 +91,7 @@
     ['gb', 'the documents that link to the open one — [[title]] links by title, [[ completes one while writing'],
     [':', 'command line — Tab / Shift-Tab cycle the matches, then the argument; ↑ ↓ recall what ran before'],
     ['Ctrl-S', 'save, from anywhere'],
-    ['?', 'this screen — in the editor too'],
+    ['?', 'this screen, from the editor too — h/l a column, / filters it down'],
   ]
 
   /* The board rebinds most keys, so it gets its own column rather than
@@ -96,139 +137,225 @@
     view: 'session',
   }
 
-  const grouped = groups.map(
-    (group) => [group, commands.filter((spec) => spec.group === group)] as [Group, CommandSpec[]],
-  )
+  type Row = { key: string; args?: string; description: string }
+
+  const fromPairs = (pairs: [string, string][]): Row[] =>
+    pairs.map(([key, description]) => ({ key, description }))
 
   /** `:write(w)` — the name first, then whatever else reaches it. */
   const signature = (spec: CommandSpec) =>
     `:${spec.name}${spec.aliases?.length ? `(${spec.aliases.join(' ')})` : ''}`
+
+  const fromSpecs = (specs: CommandSpec[]): Row[] =>
+    specs.flatMap((spec) => [
+      { key: signature(spec), args: spec.args, description: spec.help },
+      ...(spec.bang ? [{ key: `:${spec.name}!`, description: spec.bang.help }] : []),
+    ])
+
+  const editorKeys: [string, string][] = [
+    ['vim', 'the full keymap — hjkl, w/b, dd, ciw, visual mode, macros; :w writes'],
+    ['drop · paste', 'an image, video or audio file attaches it'],
+    ['$x^2$ · $$…$$', 'set as math'],
+    [':12', 'jumps straight to entry 12'],
+    ['y · d', 'copied to the system clipboard — :set noclipboard keeps them in the registers'],
+    ['files', 'open in place — pdf, text and code, markdown, csv, certificates and keystores'],
+  ]
+
+  const sections: [string, Row[]][] = [
+    ['keys', fromPairs(keys)],
+    ['board keys', fromPairs(boardKeys)],
+    ['agenda keys', fromPairs(agendaKeys)],
+    ['in the editor', fromPairs(editorKeys)],
+    ...groups.map((group: Group) => [titles[group], fromSpecs(commands.filter((spec) => spec.group === group))] as [string, Row[]]),
+  ]
+
+  const shown = $derived.by(() => {
+    const words = helpFilter.text.trim().toLowerCase().split(/\s+/).filter(Boolean)
+    if (words.length === 0) return sections
+    const hit = (row: Row) => {
+      const text = `${row.key} ${row.args ?? ''} ${row.description}`.toLowerCase()
+      return words.every((word) => text.includes(word))
+    }
+    return sections.map(([title, rows]) => [title, rows.filter(hit)] as [string, Row[]]).filter(([, rows]) => rows.length > 0)
+  })
+  const count = $derived(shown.reduce((sum, [, rows]) => sum + rows.length, 0))
+  const filtering = $derived(helpFilter.text.trim() !== '')
+
+  /* What a row says before its first dash is enough to find it by; the rest
+     comes back once a filter has narrowed the sheet down to a few. */
+  const brief = (description: string) => description.split(' — ')[0]
+  /** The key column of a section, as wide as its longest key, within reason. */
+  const keyWidth = (rows: Row[]) => Math.min(Math.max(...rows.map((row) => Math.max(row.key.length, row.args?.length ?? 0))), 14)
+
+  // A filter left over from last time would hide rows without saying so.
+  helpFilter.text = ''
+
+  /* The field takes its own Enter and Esc, so they settle the filter
+     instead of closing the help underneath it. */
+  function filterKey(event: KeyboardEvent) {
+    if (event.key !== 'Escape' && event.key !== 'Enter') return
+    event.preventDefault()
+    event.stopPropagation()
+    if (event.key === 'Escape') helpFilter.text = ''
+    field?.blur()
+    field?.closest<HTMLElement>('.overlay')?.focus()
+  }
 </script>
 
 <div class="sheet">
   <header>
-    <span class="label rule"><span class="marker"></span><span class="title">help</span> everything is a key or a `:` command</span>
+    <span class="label rule"><span class="marker"></span><span class="title">help</span> {count} keys and commands</span>
+    <label class="filter" class:on={helpFilter.text !== ''}>
+      <span class="slash">/</span>
+      <input
+        bind:this={field}
+        bind:value={helpFilter.text}
+        onkeydown={filterKey}
+        placeholder="filter"
+        spellcheck="false"
+        autocomplete="off"
+      />
+    </label>
     <button onclick={() => (workspace.overlay = 'none')}>esc</button>
   </header>
 
-  <div class="cols">
-    <section class="keys">
-      <h2>keys</h2>
-      <dl>
-        {#each keys as [key, description] (key)}
-          <dt>{key}</dt>
-          <dd>{description}</dd>
-        {/each}
-      </dl>
-    </section>
-
-    <section class="keys">
-      <h2>board keys</h2>
-      <dl>
-        {#each boardKeys as [key, description] (key)}
-          <dt>{key}</dt>
-          <dd>{description}</dd>
-        {/each}
-      </dl>
-    </section>
-
-    <section class="keys">
-      <h2>agenda keys</h2>
-      <dl>
-        {#each agendaKeys as [key, description] (key)}
-          <dt>{key}</dt>
-          <dd>{description}</dd>
-        {/each}
-      </dl>
-    </section>
-
-    {#each grouped as [group, specs] (group)}
-      <section>
-        <h2>{titles[group]}</h2>
+  <div class="cols" bind:this={pages}>
+    {#each shown as [title, rows] (title)}
+      <section style="--key: {keyWidth(rows)}ch">
+        <h2>{title}</h2>
         <dl>
-          {#each specs as spec (spec.name)}
-            <dt>
-              {signature(spec)}{#if spec.args}<span class="args muted">{spec.args}</span>{/if}
-            </dt>
-            <dd>{spec.help}</dd>
-            {#if spec.bang}
-              <dt>:{spec.name}!</dt>
-              <dd>{spec.bang.help}</dd>
-            {/if}
+          {#each rows as row (row.key)}
+            {@const short = filtering ? row.description : brief(row.description)}
+            <div class="row">
+              <dt>{row.key}{#if row.args}<span class="args">{row.args}</span>{/if}</dt>
+              <dd>{short}{#if short !== row.description && !short.endsWith('…')}<span class="more" title={row.description}> …</span>{/if}</dd>
+            </div>
           {/each}
         </dl>
       </section>
+    {:else}
+      <p class="none">nothing matches "{helpFilter.text}"</p>
     {/each}
   </div>
 
-  <footer>
-    inside the editor the full vim keymap is live — hjkl, w/b, dd, ciw, visual mode, macros, and
-    <span class="key">:w</span> to write. drop or paste an image, video or audio file into the
-    editor to attach it. <span class="key">$x^2$</span> and <span class="key">$$…$$</span> are set as math. a file opens in place — pdf, text and code, markdown, csv, and
-    certificates and keystores, which ask for their password. <span class="key">:12</span> jumps straight to entry 12. yanks and
-    deletes are copied to the system clipboard —
-    <span class="key">:set noclipboard</span> keeps them in vim's registers.
-  </footer>
+  {#if !isTouchDevice}
+    <footer class="label">
+      <span class="kbd">h</span><span class="kbd">l</span> column
+      <span class="gap"></span>
+      <span class="kbd">⌃d</span><span class="kbd">⌃u</span> page
+      <span class="gap"></span>
+      <span class="kbd">g</span><span class="kbd">G</span> start · end
+      <span class="gap"></span>
+      <span class="kbd">/</span> filter, and read the lines whole
+      <span class="gap"></span>
+      <span class="kbd">?</span><span class="kbd">esc</span> close
+    </footer>
+  {/if}
 </div>
 
 <style>
-  /* A free-standing panel, as the desktop draws one: hull, one rim, the frame's radius. */
+  /* A free-standing panel, as the desktop draws one: hull, one rim, the
+     frame's radius — as big as the porthole, so nothing hides below it. */
   .sheet {
     display: flex;
     flex-direction: column;
-    gap: 18px;
-    max-height: 100%;
+    gap: 14px;
+    width: 100%;
+    height: 100%;
+    min-height: 0;
     background: color-mix(in oklab, var(--hull) 97%, transparent);
     border: 1px solid var(--surface-alt);
     border-radius: var(--frame-radius);
-    padding: 20px 24px;
+    padding: 18px 22px 14px;
   }
 
   header { display: flex; align-items: center; gap: 12px; }
   header .label { flex: 1; }
   header .marker { background: var(--light); }
   header .title { color: var(--light); }
-  .sheet { width: min(100%, 112ch); overflow-y: auto; overflow-x: hidden; }
 
-  /* Newspaper columns, so the short groups fill the gaps under the long ones. */
-  .cols { columns: 44ch; column-gap: 36px; }
+  .filter {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    width: 24ch;
+    padding: 0 8px;
+    border: 1px solid var(--rim);
+    border-radius: var(--radius-s);
+    color: var(--muted);
+  }
+  .filter:focus-within, .filter.on { border-color: var(--outline); color: var(--light); }
+  .filter input {
+    flex: 1;
+    min-width: 0;
+    padding: 4px 0;
+    border: 0;
+    background: none;
+    color: var(--light);
+    font: inherit;
+    font-size: 12px;
+    outline: none;
+  }
 
-  section { break-inside: avoid; min-width: 0; margin: 0 0 20px; }
+  /*
+   * Newspaper columns of a fixed height, so they fill across before they
+   * run off the right edge, where h/l reach them. A group may break between
+   * columns, but never straight after its heading.
+   */
+  .cols {
+    flex: 1;
+    min-height: 0;
+    columns: 40ch;
+    column-gap: 28px;
+    column-fill: auto;
+    column-rule: 1px solid var(--surface-alt);
+    overflow-x: auto;
+    overflow-y: hidden;
+    scrollbar-width: none;
+  }
+
+  section { margin: 0 0 12px; }
 
   h2 {
     display: flex;
     align-items: center;
-    gap: 12px;
-    margin: 0 0 8px;
+    gap: 10px;
+    margin: 0 0 6px;
     font-size: 10px;
     font-weight: 400;
     letter-spacing: 0.22em;
     text-transform: uppercase;
     color: var(--muted);
+    break-after: avoid;
   }
   h2::after { content: ''; height: 1px; flex: 1; background: var(--overlay); }
 
-  /* The key column is capped, so one long signature cannot squeeze every
-     description in its group down to a letter a line; arguments wrap
-     underneath the name instead. */
-  dl {
-    margin: 0;
+  /* One row is never split between columns. The key column is as wide as
+     the section's longest key up to a cap, so one long signature cannot
+     squeeze every description down; arguments wrap under the name. */
+  dl { margin: 0; font-size: 12px; line-height: 1.35; }
+  .row {
     display: grid;
-    grid-template-columns: fit-content(20ch) minmax(0, 1fr);
-    gap: 7px 16px;
-    font-size: 13px;
-    line-height: 1.45;
+    grid-template-columns: var(--key) minmax(0, 1fr);
+    gap: 12px;
+    padding: 1px 0;
+    break-inside: avoid;
   }
-  dt { color: var(--light); white-space: nowrap; }
-  .args { display: block; white-space: normal; font-size: 11px; }
-  dd { margin: 0; color: var(--fg); overflow-wrap: break-word; }
+  dt { color: var(--light); overflow-wrap: break-word; }
+  .args { display: block; font-size: 10px; color: var(--muted); }
+  dd { margin: 0; color: var(--subtle); overflow-wrap: break-word; }
+  .more { color: var(--outline); }
 
-  footer {
-    font-size: 12px;
-    color: var(--muted);
-    border-top: 1px solid var(--overlay);
-    padding-top: 12px;
-    line-height: 1.7;
+  .none { margin: 0; color: var(--subtle); font-size: 12px; }
+
+  footer { display: flex; flex-wrap: wrap; align-items: center; gap: 4px; font-size: 10px; }
+  footer .kbd { margin-right: 2px; }
+  footer .gap { width: 14px; }
+
+  /* A phone stacks the columns and scrolls the sheet down. */
+  @media (max-width: 767px) {
+    .sheet { overflow-y: auto; }
+    .cols { flex: none; columns: auto; overflow: visible; }
+    .filter { width: 14ch; }
   }
-  .key { color: var(--light); }
 </style>