Desktop Plugin SDK

The native Hermes Desktop app is contribution-driven: every surface in the window — panes, routes, sidebar nav, status-bar items, palette entries, keybinds, themes — registers into one central registry. Core registers its surfaces exactly the way a plugin does, so the plugin story is the real one, not a bolted-on afterthought.

A desktop plugin is a single ESM file that default-exports a HermesPlugin. It imports one module — @hermes/plugin-sdk — and gets everything: the app's live state, the gateway JSON-RPC door, a scoped REST/socket backend namespace, React Query, and the app's own UI kit so plugin UI looks native by default. No repo clone, no npm run build, no patching app source. Drop the file in $HERMES_HOME/desktop-plugins/<id>/plugin.js and the app loads it within seconds and hot-reloads every save.

This is not the web-dashboard plugin SDK

"Plugin" means several unrelated things across Hermes. This page is the native desktop app (hermes desktop) SDK — the @hermes/plugin-sdk module and $HERMES_HOME/desktop-plugins/. The web dashboard (hermes dashboard) has its own, unrelated plugin system on window.__HERMES_PLUGIN_SDK__ with a manifest.json — documented at Extending the Dashboard. Python CLI/gateway plugins are documented at Build a Hermes Plugin. The three do not share code, APIs, or delivery. Only the backend plugin_api.py namespace (/api/plugins/<id>) is shared between the desktop and dashboard SDKs.

Mental model

The SDK follows the VS Code module model. A plugin author imports exactly one module and never touches app internals (they are lint-fenced out of a bundled plugin, and fail to resolve in a disk plugin). Capability comes in tiers:

• host.state.* — readonly views over the app's live state (nanostore atoms): active session, per-session turn-busy, cwd, gateway socket status, model, profile, viewport. gateway is the WebSocket, not turn-busy.
• host.* actions — curated safe verbs: toast, navigate, tail logs, restart the gateway, subscribe to the gateway event stream.
• host.request — the gateway JSON-RPC door: sessions, config, skills, cron — everything the app itself calls.
• ctx.rest / ctx.socket — your plugin's own backend namespace (/api/plugins/<id>) if you ship a plugin_api.py.
• ui.* — the design language: the app's real components, theme variables, icons, and formatters, so your UI matches the app pixel-for-pixel.

Two delivery modes

Mode	Where	Who	Build step
Disk (recommended)	$HERMES_HOME/desktop-plugins/<id>/plugin.js	users, agents	none — plain ESM, loaded uncompiled
Unified package	$HERMES_HOME/plugins/<id>/desktop/plugin.js	plugins that also ship agent-side code	none — same disk pipeline
Bundled	apps/desktop/src/plugins/<id>/plugin.tsx	in-tree, shipped with the app	the app's own Vite build

All three take the same HermesPlugin contract, appear in Capabilities → Plugins, and enable/disable live. A unified package is just the disk door scanning inside your agent plugin's folder — see One package, both SDKs. Everything on this page is written against the disk door (what you and the agent write); Bundled plugins notes the two differences. Radio ships as a bundled SDK-only plugin, off by default. Enable it in Capabilities → Plugins for free live streams, station search, and status-bar playback controls with an audio-reactive waveform. It uses the existing plugin toggle and contributes nothing while disabled. Reference demos live in the companion hermes-example-plugins repo.

Quick start — your first plugin

Create $HERMES_HOME/desktop-plugins/hello/plugin.js (that's ~/.hermes/... by default). Desktop plugins are app-level — one root for every profile, gateway, or remote machine the window connects to. The folder name must equal the plugin id.

// ~/.hermes/desktop-plugins/hello/plugin.js
import { host, haptic, useValue } from '@hermes/plugin-sdk'
import { jsx, jsxs } from 'react/jsx-runtime'

function HelloPane() {
  const gateway = useValue(host.state.gateway)

  return jsxs('div', {
    className: 'flex h-full flex-col gap-2 p-3 text-sm',
    children: [
      jsx('div', { className: 'font-medium', children: 'Hello, Hermes' }),
      jsx('div', {
        className: 'text-(--ui-text-tertiary)',
        children: `gateway: ${gateway}`
      })
    ]
  })
}

export default {
  id: 'hello', // must match the folder name
  name: 'Hello',
  register(ctx) {
    ctx.register({
      id: 'pane',
      area: 'panes',
      title: 'hello',
      data: { placement: 'right', width: '260px' },
      render: () => jsx(HelloPane, {})
    })
    ctx.register({
      id: 'chip',
      area: 'statusBar.right',
      order: 130,
      render: () =>
        jsx('button', {
          type: 'button',
          className: 'px-1.5 text-[0.6875rem] text-(--ui-text-tertiary)',
          onClick: () => {
            haptic('tap')
            host.notify({ kind: 'info', message: 'Hello from my plugin!' })
          },
          children: 'hello'
        })
    })
  }
}

Save it. The app watches desktop-plugins/, loads the file within a few seconds, and hot-reloads every later save in place. If it doesn't appear, run ⌘K → Reload desktop plugins. If loading fails, a toast names the error — fix and save again.

:::note No JSX, no build The disk file is loaded uncompiled, so JSX syntax will not parse. Write UI with jsx() / jsxs() calls from react/jsx-runtime (or React.createElement). The only importable specifiers are @hermes/plugin-sdk, react, and react/jsx-runtime — everything else fails to resolve, on purpose. :::

The plugin contract

A plugin default-exports a HermesPlugin:

interface HermesPlugin {
  /** Stable slug — becomes the `plugin:<id>` source and the id namespace. */
  id: string
  /** Human name for Settings / about UI. Defaults to `id`. */
  name?: string
  /** Registers on load when the user hasn't chosen (default true). Set false
   *  for opt-in plugins: they inventory in Capabilities ▸ Plugins, off until the
   *  user flips the switch. */
  defaultEnabled?: boolean
  /** Called once at load; wire contributions through `ctx`. */
  register: (ctx: PluginContext) => void
}

register receives a scoped PluginContext. It never touches the registry directly — the context auto-tags provenance (source: 'plugin:<id>') and namespaces every contribution id (<id>:<localId>), so two plugins can never collide.

interface PluginContext {
  /** Resolved source tag, e.g. `'plugin:hello'`. */
  readonly source: string
  /** Register one contribution (id namespaced, source stamped). Returns a disposer. */
  register: (c: PluginContribution) => () => void
  /** Register several at once; the returned disposer removes all of them. */
  registerMany: (cs: PluginContribution[]) => () => void
  /** REST to this plugin's own backend namespace (`/api/plugins/<id>`). */
  rest: <T>(path: string, opts?: PluginRestOptions) => Promise<T>
  /** Live WebSocket to this plugin's own namespace. Returns a disposer. */
  socket: (path: string, onMessage: (data: unknown) => void) => () => void
  /** The curated OS door: native notification, open-external, reveal-in-file-manager, clipboard. */
  os: PluginOs
  /** Plugin-scoped JSON persistence (keys live under `hermes.plugin.<id>.`). */
  storage: PluginStorage
}

A contribution is the one primitive every surface shares:

interface Contribution {
  id: string          // you write the local id; the host namespaces it
  area: string        // WHERE it goes (a contribution-area constant)
  title?: string
  order?: number      // sort within the area (lower = earlier)
  when?: () => boolean // dynamic visibility; re-evaluated by the area
  enabled?: boolean
  render?: () => ReactNode  // the component to mount
  data?: unknown      // area-specific payload (see the cookbook)
}

You provide render, data, or both, depending on the area.

Contribution areas — the cookbook

Import the area constants from the SDK; each area has its own data payload.

Surface	area	You provide
Layout pane	PANES_AREA ('panes')	title + render + data: { placement, dock?, width?, height? }
Full page	ROUTES_AREA	data: { path } + render
Sidebar nav	SIDEBAR_NAV_AREA	data: { path, label, codicon }
Status bar	STATUSBAR_AREAS.left / .right	render (or data as StatusbarItem)
Title bar	TITLEBAR_AREAS.left / .center / .right	data as TitlebarTool, or a mount-scoped <Contribute>
⌘K palette	PALETTE_AREA	data: PaletteContribution
Keybind	KEYBINDS_AREA	data: KeybindContribution
Theme	THEMES_AREA	data as a DesktopTheme
Composer	COMPOSER_AREAS.*	render slots, or middleware / attachment providers

Panes

A pane is a tile in the layout tree. placement is the semantic role — the pane stacks (as tabs) with existing panes of that role; the user can drag it anywhere afterward.

ctx.register({
  id: 'pane',
  area: 'panes',
  title: 'my pane',
  data: { placement: 'right', width: '260px' },
  render: () => jsx(MyPane, {})
})

placement is 'main' | 'left' | 'right' | 'top' | 'bottom'. To land on a specific edge instead of stacking, add a dock gesture — the same thing as dragging onto a pane's drop chip:

// Below the conversation, 200px tall.
data: {
  placement: 'bottom',
  dock: { pane: 'workspace', pos: 'bottom' },
  height: '200px'
}

dock.pane is any pane id (workspace is the main thread; also sessions, terminal, files, review, logs); dock.pos is 'top' | 'bottom' | 'left' | 'right' | 'center'. Declare a width/height so the pane doesn't claim half the zone.

Closing the only pane contributed by a plugin disables that plugin, which can be re-enabled from Capabilities → Plugins. When a plugin contributes multiple panes, closing one dismisses only that pane and leaves the plugin's other panes, commands, and middleware active. Reset layout restores dismissed contributed panes.

Pages and sidebar nav

A route mounts a full page in the workspace pane, like any built-in view. Pair it with a sidebar nav row (and/or a palette command) to make it reachable.

import { ROUTES_AREA, SIDEBAR_NAV_AREA } from '@hermes/plugin-sdk'

ctx.registerMany([
  {
    id: 'page',
    area: ROUTES_AREA,
    data: { path: '/my-page' },
    render: () => jsx(MyPage, {})
  },
  {
    id: 'nav',
    area: SIDEBAR_NAV_AREA,
    data: { path: '/my-page', label: 'My Page', codicon: 'project' }
  }
])

codicon is a VS Code codicon id. Navigate to a route from anywhere with host.navigate('/my-page').

Status bar and title bar

Status-bar items render into the left or right cluster of the bottom bar. Simplest is a render function; for a plain button use data as a StatusbarItem ({ id, label?, icon?, detail?, variant?, menuItems?, … }).

import { STATUSBAR_AREAS, TITLEBAR_AREAS } from '@hermes/plugin-sdk'

ctx.register({
  id: 'count',
  area: STATUSBAR_AREAS.right,
  order: 120,
  render: () => jsx(MyStatus, {})
})

Title-bar tools live in TITLEBAR_AREAS.left | .center | .right as TitlebarTool data ({ id, label, icon, active?, onSelect? }).

Palette commands and keybinds

import { PALETTE_AREA, KEYBINDS_AREA } from '@hermes/plugin-sdk'

ctx.registerMany([
  {
    id: 'open',
    area: PALETTE_AREA,
    data: {
      id: 'my-page.open',
      label: 'Open My Page',
      keywords: ['my', 'page'],
      run: () => host.navigate('/my-page')
    }
  },
  {
    id: 'refresh',
    area: KEYBINDS_AREA,
    data: {
      id: 'my-page.refresh',
      label: 'Refresh My Page',
      category: 'My Plugin',
      defaults: ['mod+shift+r'],
      run: () => void doRefresh()
    }
  }
])

Keybinds are user-rebindable in settings; defaults is just the initial binding.

Themes

A theme contribution ships a full DesktopTheme as its data (name, label, colors, …). It appears in the theme picker like a built-in.

import { THEMES_AREA } from '@hermes/plugin-sdk'

ctx.register({ id: 'noir', area: THEMES_AREA, data: myDesktopTheme })

Registering a theme lists it; it does not select it. useTheme() reads the painted appearance (theme, themeName, availableThemes, resolvedMode) and changes it (setTheme, setMode, previewTheme) from a component:

import { Button, useTheme } from '@hermes/plugin-sdk'

function ThemePicker() {
  const { availableThemes, setTheme, themeName } = useTheme()

  return availableThemes.map(t => (
    <Button key={t.name} disabled={t.name === themeName} onClick={() => setTheme(t.name)}>
      {t.label}
    </Button>
  ))
}

A switch driven by something other than a render — a gateway connecting, a socket event, any host.onEvent callback — has no component to hang the hook on. Use requestTheme(name) there. An unresolvable name is refused rather than coerced to the default skin, so the return value doubles as the availability check and a wrong name can never silently reset someone's appearance:

import { host, requestTheme } from '@hermes/plugin-sdk'

host.onEvent('gateway.ready', () => {
  if (!requestTheme('noir')) {
    host.notifyError('Connected, but the noir theme is not installed.')
  }
})

Both doors persist per profile, so a plugin-driven switch sticks exactly like a manual pick. To tint the active theme rather than replace it, use setAccentOverride(hex) and clear it in ctx.onDispose — the standalone Accent Picker plugin is the worked example (it is also a complete, installable disk plugin).

Composer extensions

COMPOSER_AREAS (top, bottom, leading, actions, attachments, middleware) let a plugin add controls around the message composer, provide an attachment source, or transform a draft before it is sent (ComposerMiddleware with a handler(draft) => draft | null).

Transcript directives — inline components the model addresses

TRANSCRIPT_DIRECTIVE_AREA makes the transcript itself a contribution area. Register a named directive and the agent can render your component inline in an assistant message by emitting a paragraph of the form ::name{key="value"}:

import { TRANSCRIPT_DIRECTIVE_AREA } from '@hermes/plugin-sdk'

ctx.register({
  id: 'task-card',
  area: TRANSCRIPT_DIRECTIVE_AREA,
  data: {
    name: 'task', // the model writes ::task{id="BB-12"}
    render: ({ attrs, streaming }) => jsx(TaskCard, { taskId: attrs.id, streaming })
  }
})

Rules the host enforces so the surface stays safe:

• The directive must be the entire paragraph — ::name mid-prose stays prose, so plugin components can never hijack running text.
• Attributes are untrusted model output (key="value" pairs, string-only). Validate your own fields; render nothing on garbage rather than guessing.
• An unclaimed directive (no plugin registered for the name) renders as the plain paragraph it always was — nothing breaks when a plugin is off.
• Renders are wrapped in the contribution error boundary: a throw degrades to an inline error chip, never a dead message.
• First registration wins on a name collision; namespace adventurous names with your slug (myplugin-board, not board).

Core ships one directive as the reference consumer: ::preview{file="…"} renders the workspace HTML file live inside the message — a sandboxed srcdoc iframe with an opaque origin (scripts run and the widget is fully interactive; no reach into the app, its storage, or the bridge). The frame sizes itself to the content (height live, width adopted from the content's intrinsic span, flush left in the message flow), and a theme prelude hands the document the app's resolved tokens (--foreground, --muted-foreground, --accent, --border, --card), the app font, and a transparent background — so widget-shaped HTML reads as native while a full page keeps its own design. Non-HTML targets and remote gateways fall back to the classic preview card. Tell the agent about your directive in a skill (that's how it learns to emit it).

Previewed widgets can also talk back. Inside the frame, window.hermes.send('get-price eth') (or a declarative <button data-hermes-send="get-price eth"> — no script needed) hands that prompt to the agent as a user turn, off-screen: no bubble takes up the transcript, the widget updating is the visible response. The turn is still real — it wakes the agent, rides the composer's steer/queue rules, and persists (typed hidden) so resume and the session DB keep the full record. Prompts are trimmed, capped at 500 chars, and throttled to one per second per frame.

Mount-scoped chrome (Contribute)

ctx.register is for permanent contributions. When chrome should live and die with a component that's already on screen (a page's own title-bar control leaves when the page unmounts), render <Contribute> inside it instead:

import { Contribute, TITLEBAR_AREAS } from '@hermes/plugin-sdk'

jsx(Contribute, {
  area: TITLEBAR_AREAS.center,
  id: 'my-page:switcher', // namespace with your slug
  children: jsx(MySwitcher, {})
})

It registers on mount and disposes on unmount automatically.

Host API

Everything on host is reachable from anywhere in a plugin. State atoms are readonly — read with .get() in handlers, subscribe with useValue(atom) in components.

host.state.activeSessionId  // ReadableAtom<string | null>
host.state.awaitingResponse // ReadableAtom<boolean>  true until the first assistant payload
host.state.busy             // ReadableAtom<boolean>  focused chat is working after a send
host.state.busyBySession    // ReadableAtom<Record<string, boolean>>  runtime id → mid-turn
host.state.focusedSessionId // ReadableAtom<string | null>  (runtime id of the FOCUSED session — tile-aware; prefer for session.* RPC)
host.state.focusedSessionProfile // ReadableAtom<string>  (owner profile of the focused chat — prefer over `profile` for per-bot/profile readouts)
host.state.focusedStoredSessionId // ReadableAtom<string | null>  (durable id — navigation / session-list matching)
host.state.focusedUsage     // ReadableAtom<UsageStats | null>  (live streamed usage of the focused session, no RPC needed)
host.state.cwd              // ReadableAtom<string>
host.state.gateway          // ReadableAtom<string>  socket state ('idle' | 'connecting' | 'open' | …)
host.state.model            // ReadableAtom<string>
host.state.profile          // ReadableAtom<string>
host.state.viewport         // ReadableAtom<{ width, height, narrow }>

host.state.gateway is the WebSocket connection, not whether a chat turn is running. A session can be mid-turn while the socket is open; another session can be idle at the same time. Disable composer or plugin actions from the focused session's turn-busy (host.state.busyBySession[sessionId], or that session's view.$busy) — never from gateway, and never from a process-global busy flag.

host.notify({ kind, message, title?, detail?, action? })  // toast; returns id
host.notifyError(error, fallbackMessage)                   // toast an error
ctx.os.notify({ title, body?, silent?, icon?, activate?, onActivate?, actions? })
                                           // native OS notification (attributed to your plugin)
ctx.os.openExternal(url)                   // OS default handler (browser, mail, spotify:) → Promise<boolean>
ctx.os.revealPath(path)                    // reveal in Finder / Explorer → Promise<boolean>
ctx.os.writeClipboard(text)                // system clipboard → Promise<boolean>
host.navigate('/route')                    // hash-route navigation
host.openSession(id, { profile?, intent? }) // open a stored session core-style;
                                           //   profile: soft-swap to that profile's backend first
                                           //   intent: 'in-place' (default) | 'stack' | 'tab' | 'window'
host.newChat(profile?)                     // fresh chat draft, optionally in another profile
host.openWorkspace(id, { render, title?, minWidth?, onClose? })
                                           // dock a plugin-rendered tab into the MAIN
                                           //   workspace zone and reveal it; returns a disposer
host.paneVisibility(paneId)                // ReadableAtom<boolean> — is a contributed pane
                                           //   actually on screen (its zone's active tab)?
host.onEvent(type, fn)                     // gateway event stream ('*' = all); returns disposer
host.logs(...)                             // tail an app log file
host.status()                              // one-shot system status snapshot
host.restartGateway()                      // restart the backend gateway
host.profileRoutes()                       // [{ profile, targetProfile, connectionId, mode }]
host.requestProfile<T>(route, method, params?)   // registry-routed RPC; no foreground swap
host.requestProfile<T>(profile, method, params?) // legacy v1/local overload
host.request<T>(method, params?)           // active-gateway JSON-RPC — the real power

host.request is the same JSON-RPC the app itself uses (sessions, config, skills, cron, kanban, …). host.requestProfile accepts a descriptor from host.profileRoutes() and routes that RPC through its exact registry source and profile without changing the active chat or gateway. The profile-only overload is retained only for the sole-local/legacy topology; registry-aware plugins should pass the descriptor so two sources exposing the same profile name cannot collide.

host.openWorkspace(id, { render, title?, minWidth?, onClose? }) docks a plugin-rendered view into the main workspace zone — the same center area session tiles and previews use — as a tab, and reveals it. Re-calling it with the same id refreshes the content in place and re-fronts the tab instead of opening a duplicate. Closing the tab (the tab's Close control or ⌘W) tears the registration down and fires your onClose; the returned disposer closes it programmatically. Feature-detect it (typeof host.openWorkspace === 'function') and fall back to a regular contributed pane on older desktop builds — Bot Mode's group-chat rooms are the reference consumer (main-window takeover when available, in-panel view otherwise).

host.paneVisibility(paneId) returns a readonly reactive atom that is true while a contributed pane is actually on screen: present in the layout tree, not dismissed or hidden, its zone un-minimized, and holding its zone's active tab slot (a lone pane in its own zone counts). The id is the contribution-scoped pane id, <pluginId>:<paneId>. Atoms are memoized per id, so calling it in render is safe. Use it to register companion UI only while your pane is visible — Bot Mode's Cronjobs pane is the reference consumer: it registers while the Bots pane holds the sidebar tab and unregisters when the user tabs back to Sessions. Feature-detect on older desktops (typeof host.paneVisibility === 'function') and fall back to always-registered behavior.

host.profileRoutes() inventories every registered source in the current connection registry. Connect-on-demand SSH sources expose a credential-free default seed route without opening a tunnel, so a plugin can be the first caller that dials them; an SSH remoteProfile remains the route's backend targetProfile. connectionId is the registry routing identity; pair it with profile for keys and persistence. Endpoint, token, SSH host/key, and other raw connection fields never cross the plugin IPC boundary. profile is the source-local route used for requests; targetProfile is the backend Hermes profile served by that route. They differ when a route explicitly maps to another backend profile (for example an SSH remoteProfile override or a legacy per-profile URL alias). This distinction preserves backend identity without exposing connection secrets.

Profile-shaped plugins get first-class methods too: profiles.list (each profile + its most recent conversation as last_session; pass include_sessions: false to skip the per-profile DB probe; pass preferred_session_ids: { profileName: sessionId } for an exact, existence-checked lookup of one pinned session per profile — each named row gains a preferred_session summary that resolves hidden rows and compression lineages to their live tip, or null when the id is definitively gone; older gateways ignore the param and omit the field) and profiles.create (name, description, clone_from, clone_all, no_skills, soul, optional model + provider pin) — the ws twins of the dashboard's /api/profiles REST routes. host.state.busy is the focused chat's live turn (thinking and streaming). host.state.awaitingResponse stays true from send until the first assistant payload. Both follow the chat the user is actually looking at — the focused session tile when one holds focus, else the primary workspace chat (the same signal the statusbar's busy pulse reads). Subscribe in a component:

const busy = useValue(host.state.busy)

For token-level detail, listen with host.onEvent (message.start, message.delta, message.complete).

host.onEvent streams live gateway events (message deltas, session lifecycle, tool activity). Listeners are isolated — a throw in your listener can't affect app dispatch. Every host door is async-safe: a sync throw from an internal helper (e.g. no desktop bridge in a plain browser) becomes a rejection your .catch() sees, never an error-boundary crash.

ctx.os is the curated OS door — every way a plugin reaches outside the app window, in one namespace attributed to your plugin. ctx.os.notify posts a native OS notification — the same Electron pipeline the app's own approval/turn alerts use. It fires only while the user is away from Hermes (backgrounded / unfocused); use host.notify for the in-app toast when they're looking at the app. Users can silence it per device under Settings ▸ Notifications ▸ "Plugin notifications", and repeats from the same plugin are throttled, so treat it as a signal for genuinely notable events — not a log.

Rich presentation + activation (extends the original ctx.os door):

ctx.os.notify({
  title: 'New match found',
  body: 'Someone matched your signal',
  icon: '/abs/path/to/icon.png', // Electron Notification icon
  // Body click → focus Hermes + navigate. Same vocabulary as OS deep links:
  activate: 'hermes://index-network/intent/1',
  // or: activate: '/index-network/intent/1'
  // or: activate: { path: '/index-network/intent/1' }
  onActivate: () => focusLocalState('1'), // optional renderer callback
  actions: [
    { id: 'open', label: 'Open', activate: 'hermes://index-network/intent/1' },
    { id: 'dismiss', label: 'Dismiss', onAction: () => dismiss('1') },
  ],
})

activate is deeplink-compatible: hermes://index-network/intent/1 and the hash path /index-network/intent/1 resolve to the same in-app route (and the same hermes://… URL works as an OS deep link). Action buttons only render on signed macOS builds; elsewhere the body click still activates. Navigation only happens on user click — never from a background event alone.

The other doors (openExternal, revealPath, writeClipboard) resolve false instead of throwing when the capability isn't available (older desktop shell, plain browser) — branch on the result rather than sniffing the bridge.

Data layer — React Query + nanostores

Plugins share the app's single QueryClient, so plugin queries cache, dedupe, poll, and invalidate exactly like core screens — never hand-roll a fetch loop.

import { useQuery, useMutation, useQueryClient, atom, computed, useValue } from '@hermes/plugin-sdk'

function MyPanel() {
  const { data, isLoading } = useQuery({
    queryKey: ['my-plugin', 'items'],
    queryFn: () => host.request('my.list', {})
  })
  // …
}

For state shared between a trigger and its panel (or a poll loop), use atom / computed — the same primitive host.state uses. Subscribe in the leaf that renders the value with useValue. To invalidate a query from outside React (e.g. a ctx.socket frame arriving), import the shared queryClient:

import { queryClient } from '@hermes/plugin-sdk'

ctx.socket('/events', () => {
  queryClient.invalidateQueries({ queryKey: ['my-plugin', 'items'] })
})

The UI kit and theming

Import the app's real components directly so your UI is native by default:

Button, Input, Textarea, Select*, Switch, Checkbox, SegmentedControl, Tabs*, Dialog*, ConfirmDialog, DropdownMenu*, ContextMenu*, Popover*, Tip/Tooltip*, Badge, Kbd/KbdGroup, SearchField, ScrollArea, Separator, Skeleton, GlyphSpinner, Loader, EmptyState, ErrorState, CopyButton, StatusDot, LogView, Codicon, DecodeText.

Plus helpers: cn (class merge), icons.* (the app's lucide set), haptic, profileColor / profileColorSoft (deterministic identity colors), the time formatters relativeTime / fmtDateTime / fmtDayTime / coarseElapsed, useI18n (localized copy — your plugin stays translatable), and evaluateRuntimeReadiness.

Style with theme variables, never hardcoded colors. Panes already sit on the app's editor background — leave the background alone and use vars for everything else: var(--ui-text-secondary), var(--ui-text-tertiary), var(--ui-text-quaternary), var(--ui-stroke-secondary), var(--ui-accent). For canvas drawing, resolve them once with getComputedStyle(canvas).getPropertyValue('--ui-accent'). This is what makes a plugin reskin automatically with every theme.

A backend for your plugin

If your plugin needs server-side work, ship a Python plugin_api.py and reach it through ctx.rest / ctx.socket — a namespace scoped to your plugin by construction.

One package, both SDKs

A feature that needs a desktop UI and agent-side code (a Python plugin, its backend routes, skills) doesn't have to ship as two co-dependent installs. Put a desktop/plugin.js inside the agent package. When the package lands in any local plugins/ root (default home or a profile), the Electron main process copies that half into $HERMES_HOME/desktop-plugins/<id>/ beside a .hermes-package.json marker, and the renderer loads it through the exact same pipeline as the standalone disk door (hot reload included):

~/.hermes/plugins/<id>/           # ONE installable folder
├── plugin.yaml                   # the agent half: tools, hooks, commands
├── skills/…
├── dashboard/
│   ├── manifest.json             # { "name": "<id>", "api": "plugin_api.py" }
│   └── plugin_api.py             # backend routes → /api/plugins/<id>/
└── desktop/
    └── plugin.js                 # the desktop half: panes, commands, ctx.rest

The desktop/plugin.js half is an ordinary disk plugin — same contract, same imports, same ctx.rest('/…') reaching the plugin_api.py sitting beside it. Installing, sharing, or removing the feature is one folder: the app-root copy is refreshed when the source plugin.js changes (hermes plugins update, or Rescan) and removed when the package folder disappears. The copy is what makes the desktop half app-level: it exists once, however many profiles carry the package, and it never appears or disappears when the user switches the Capabilities profile selector. The renderer never scans plugins/ itself. The marker records the package name and its origin (catalog sidecar or git remote), which is what the Install here button on the Plugins page uses to install the agent half into another profile.

Two enable switches still apply, on purpose, and both default to off: the desktop half ships opt-in — it inventories in Capabilities → Plugins but stays disabled until the user toggles it — matching the Python half's plugins.enabled gate in config.yaml (the security boundary below). Dropping a package into ~/.hermes/plugins is inert on every surface until the user says otherwise. The desktop half degrades gracefully when the backend half is off — ctx.rest returns errors, not crashes.

:::note The copy is local to the machine the desktop app runs on. Against a remote backend, the remote box's ~/.hermes/plugins is not reachable as a filesystem — only locally installed packages contribute a desktop half this way. For a remote backend the install dialog clones the desktop half separately into desktop-plugins/, the same as a desktop-only repo. :::

Distributing with an install link

Ship your plugin repo (agent half, desktop half, or both) and link to it with the hermes:// scheme — a plain anchor on your website or README:

<a href="hermes://plugin/install?repo=owner/repo&enable=1">Install in Hermes</a>

The user gets a confirmation dialog (repo id, source links, a probe of what the repo ships) and picks components before anything is installed — deep links never auto-install. force=1 replaces an existing install; dev builds use hermes-dev://. Full link reference: One-click install links.

The Python side

Desktop plugins reuse the dashboard plugin backend mount. Put the backend in a dashboard/ subfolder of a regular Hermes plugin and declare it in a manifest.json:

~/.hermes/plugins/<id>/
└── dashboard/
    ├── manifest.json      # { "name": "<id>", "api": "plugin_api.py" }
    └── plugin_api.py      # exports `router = APIRouter()`

# plugin_api.py
from fastapi import APIRouter

router = APIRouter()

@router.get("/board")
async def board():
    return {"items": ["one", "two", "three"]}

@router.post("/action")
async def action(body: dict):
    return {"ok": True, "received": body}

Routes mount under /api/plugins/<id>/ (GET /api/plugins/<id>/board, …). Backend code runs inside the gateway process, so it can import from the hermes-agent codebase directly (hermes_state, hermes_cli.config, …). See Extending the Dashboard → Backend API routes for the full backend reference — the mount is identical.

:::caution The Python backend is gated separately Enabling a plugin in the desktop Capabilities → Plugins panel is a renderer-side choice; it does not import Python. A user plugin's plugin_api.py is imported only when the plugin is in the plugins.enabled allow-list in config.yaml (and not in plugins.disabled). Project plugins (./.hermes/) never auto-import Python. This is a security boundary, not an oversight (GHSA-mcfc-hp25-cjv7). :::

Calling it from the plugin

register(ctx) {
  // REST — namespace-relative path.
  const load = () => ctx.rest('/board')                 // GET /api/plugins/<id>/board
  const act  = () => ctx.rest('/action', { method: 'POST', body: { go: true } })

  // Live twin — a WebSocket to your own namespace.
  const stop = ctx.socket('/events', frame => {
    queryClient.invalidateQueries({ queryKey: [ctx.source, 'board'] })
  })
}

ctx.rest is profile-aware and rejects path traversal (..) so you can never address another plugin's API or a core route through it. PluginRestOptions is { method?, body?, upload?: { filename, contentType?, bytes }, timeoutMs? }.

ctx.socket auto-reconnects with backoff until disposed. It resolves to a no-op on OAuth remotes (single-use WS tickets are core-managed) — treat the socket as an accelerator over polling, never a replacement. Every consumer needs a polling fallback anyway, since any socket can drop.

For gateway-wide data (not your own namespace), use host.request (JSON-RPC) and host.onEvent (the gateway event stream) instead.

Settings, enable state, and storage

Every plugin — enabled or not — inventories in Capabilities → Plugins, where the user toggles it live (no app restart), reveals its folder, or rescans. The user's choice is remembered:

• No choice yet → the plugin's own defaultEnabled (default true). Set defaultEnabled: false to ship an opt-in plugin that stays dark until the user flips it on.
• Explicit choice → persisted and honored across restarts. A disabled plugin stays disabled — don't fight it; the user turned you off.

Persist your own state with ctx.storage, namespaced to your plugin (hermes.plugin.<id>.*) so plugins can't read or clobber each other:

ctx.storage.set('lastTab', 'board')
const tab = ctx.storage.get('lastTab', 'summary')
ctx.storage.remove('lastTab')

Bundled plugins

A plugin can ship in-tree at apps/desktop/src/plugins/<id>/plugin.tsx (default export a HermesPlugin). It's discovered by discoverBundledPlugins() at boot — no import, no registry edit — and shares the exact inventory + live enable/disable contract as a disk plugin. The two differences:

1. It goes through the app's Vite build, so you can write real JSX and import the SDK by its @hermes/plugin-sdk alias.
2. It's still lint-fenced to @hermes/plugin-sdk + react only — no @/… app internals.

No desktop plugins ship in the core tree today; the shipped app stays uncluttered and demos live in the hermes-example-plugins companion repo.

Security model

A loaded plugin is evaluated as ESM in the renderer realm with full app authority — the React singleton, the whole SDK (host.request gateway RPC, ctx.rest, storage, navigate). The isolation the loader provides is error isolation only: a plugin can't crash the app (contributions are error-bounded, listeners isolated), but it can do anything the app can.

This is acceptable for local sources — a disk file can already run code on your machine — which is why the disk door only loads local files you (or your agent) wrote. The optional integrity (sha256-…) check only proves the bytes match a hash; it does not sandbox. A future remote-source door will need a real boundary (iframe/worker + CSP + capability gating) before it can land; do not treat this pipeline as a trust boundary.

Pitfalls

• JSX won't parse in a disk plugin. The file loads uncompiled — use jsx() / jsxs() (or React.createElement), not JSX syntax. (Bundled plugins are built, so JSX is fine there.)
• Only three specifiers resolve: @hermes/plugin-sdk, react, react/jsx-runtime. Any other import surfaces an up-front load error.
• Never hardcode colors (#000, black, rgb(...)). Leave the background alone; use theme variables (var(--ui-*)) for everything.
• Reference only what you imported. A component you forgot to import (e.g. StatusDot) is a ReferenceError at render — double-check every identifier in your jsx() calls appears in the import line.
• Read state imperatively in handlers ($atom.get()), never from a render closure — rapid events will otherwise see stale values. Subscribe (useValue) only in the leaf that renders the value.
• Canvas panes must track their container with a ResizeObserver and resize the canvas (width/height attributes, not just CSS) — panes resize constantly.
• Don't poll faster than a few seconds with host.request; prefer host.onEvent / ctx.socket and let React Query dedupe.
• ctx.socket is a no-op on OAuth remotes. Always have a polling fallback.

Reference

SDK exports at a glance

Category	Exports
Host	host (.state.*, .notify, .notifyError, .navigate, .onEvent, .logs, .status, .restartGateway, .request)
Plugin contract	HermesPlugin, PluginContext, PluginContribution, PluginStorage, PluginOs, PluginRestOptions, PluginNativeNotificationInput, PluginNotificationAction, HermesOpenTarget, Contribution
Area constants	PANES_AREA, ROUTES_AREA, SIDEBAR_NAV_AREA, STATUSBAR_AREAS, TITLEBAR_AREAS, PALETTE_AREA, KEYBINDS_AREA, THEMES_AREA, COMPOSER_AREAS
Area payloads	RouteContribution, SidebarNavContribution, StatusbarItem, TitlebarTool, PaletteContribution, KeybindContribution, ComposerMiddleware, ComposerAttachmentProvider
React / state	useValue, atom, computed, useQuery, useMutation, useQueryClient, queryClient, Contribute
Theming	useTheme, requestTheme, setAccentOverride, $accentOverride, retintTheme, themeHue, DesktopTheme, DesktopThemeColors, plus OKLCH math (hexToOklch, oklchToHex, oklchToSrgb255, mixOklab, maxChroma, hueDelta, contrastRatio, readableOn, normalizeHex)
UI kit	Button, Input, Textarea, Select*, Switch, Checkbox, SegmentedControl, Tabs*, Dialog*, ConfirmDialog, DropdownMenu*, ContextMenu*, Popover*, Tip/Tooltip*, Badge, Kbd/KbdGroup, SearchField, ScrollArea, Separator, Skeleton, GlyphSpinner, Loader, EmptyState, ErrorState, CopyButton, StatusDot, LogView, Codicon, DecodeText
Helpers	cn, icons, haptic, useI18n, profileColor, profileColorSoft, relativeTime, fmtDateTime, fmtDayTime, coarseElapsed, evaluateRuntimeReadiness

The canonical, always-current export list is apps/desktop/src/sdk/index.ts.

Agents: the hermes-desktop-plugins skill

When an agent writes a desktop plugin, it should load the bundled hermes-desktop-plugins skill — it carries the same contract as this page in agent-facing form, with a ready-to-copy templates/plugin.js. This page is the human/developer reference; the skill is the working checklist.

Troubleshooting

My plugin doesn't appear. Confirm the file is at $HERMES_HOME/desktop-plugins/<id>/plugin.js and the folder name matches the export id. Run ⌘K → Reload desktop plugins. Check the app for an error toast naming the failure, and tail hermes logs gui -f.

"unsupported import" on load. A disk plugin may only import @hermes/plugin-sdk, react, and react/jsx-runtime. Remove any other import.

A jsx element renders nothing / throws ReferenceError. An identifier used in a jsx() call isn't imported. Add it to the import line.

ctx.rest returns 404. The backend isn't mounted: confirm ~/.hermes/plugins/<id>/dashboard/manifest.json has "api": "plugin_api.py", that the plugin is in plugins.enabled in config.yaml, and restart the gateway (backend routes mount at startup). Tail ~/.hermes/logs/errors.log for Failed to load plugin <id> API routes.

ctx.socket never fires. On an OAuth remote it's a no-op by design — use your polling fallback. Otherwise verify the backend exposes the matching @router.websocket(...) route under its namespace.

Colors look wrong after a theme switch. You hardcoded a color. Replace it with a var(--ui-*) theme variable.