Build Termy Plugins

Build small, native-feeling Termy extensions against the real v1 contract. Keep the plugin scoped, use the fewest capabilities, and verify behavior inside Termy when the user authorizes installation or development mode.

Start from evidence

1. Inspect repository instructions, the dirty state, and existing plugin files.

Preserve unrelated work.

1. Read the plugin's managed termy.d.ts when available. Treat it and the current

Termy checkout as authoritative when they differ from this skill.

1. Read [references/api-reference.md](references/api-reference.md) before adding a

new API surface or diagnosing a type/manifest error.

1. Read [references/performance-security.md](references/performance-security.md)

before handling user-controlled shell text, files, credentials, network, subprocesses, lifecycle events, storage, or native UI.

1. Read [references/examples.md](references/examples.md) before scaffolding. Reuse

assets/command-plugin/ or assets/native-ui-plugin/ when it fits.

Do not invent React, HTML, CSS, GPUI access, package imports, SDK imports, build hooks, or APIs that are absent from the v1 declarations.

Choose the shape

Capabilities gate Termy-owned APIs only. They do not restrict Bun's operating-system access.

Build the plugin

1. Scaffold

Prefer Termy's scaffold when its CLI is available:

termy plugin init my-plugin

Otherwise create only plugin.json and plugin.ts or plugin.tsx. Add local relative modules only when they improve the design. Do not add package.json, dependencies, or a bundler for a v1 plugin.

2. Write the manifest

Use the public schema, API version 1, a stable lowercase ID, a human-readable name, an optional display version, an optional relative main, and only required capabilities:

{
  "$schema": "https://termy.sh/schemas/plugin.schema.json",
  "apiVersion": 1,
  "id": "git-tools",
  "name": "Git Tools",
  "version": "1.0.0",
  "capabilities": []
}

Keep main inside the plugin directory. Never use absolute paths, .., or symlinks.

3. Implement against ambient types

Export one definition and let Termy's managed declarations provide the API:

export default definePlugin({
  commands: [],
} satisfies TermyPlugin);

Do not import definePlugin, TermyPlugin, TermyPluginContext, TermyUI, or an SDK. Termy supplies them globally.

Apply these rules:

• Give commands stable IDs and clear, searchable titles.
• Treat context as a read-only point-in-time snapshot. Check optional selection,

directory, command, tab, pane, and event fields before use.

• Use typed settings for configuration. Use secret settings for credentials.
• Prefer terminal.sendText and terminal.open over legacy terminal.run. Use a

structured program launch when shell parsing is unnecessary, and never concatenate untrusted free-form input into a shell command.

• Use when to hide context-specific commands, async pick inputs for bounded

dynamic choices, context.origin for stable async targeting, and context.signal/context.progress for cancellable long-running work.

• Return typed actions or emit toasts; do not reach into Termy internals.
• Use commands: [] for event-only plugins. Keep event handlers bounded.
• Use async storage for small JSON and managed paths for larger files.
• Use .tsx, the three Termy JSX pragmas, allowlisted TermyUI components, unique

control IDs, named actions, and onAction for interactive native views. Pass bounded JSON params for navigation and use view.replace/view.close for flows.

• Paginate dynamic native-UI lists and rerender from persisted state.

Develop and verify

Do not mutate the user's installed plugins merely to inspect code. When the user only requested source work, perform a non-installing syntax/import check first:

termy_plugin_check_dir="$(mktemp -d)"
bun build ./my-plugin/plugin.ts --target=bun --outdir "$termy_plugin_check_dir"

Use the .tsx entrypoint when applicable. This mirrors Termy's Bun target but does not prove ambient type compatibility or Termy runtime behavior.

When the user asked to build/run the plugin and Termy is installed, use:

termy plugin dev ./my-plugin

This validates the source tree, atomically syncs valid changes, and watches the development folder. Open the command palette after saving to refresh the current plugin. Stop the watcher with Ctrl-C; this does not uninstall the managed copy.

Verify the relevant surfaces:

1. Confirm the manifest validates and the Worker loads without a Bun error.
2. Exercise every command, input branch, contextual when state, action, and toast.
3. Test missing optional context and both native/tmux behavior when relevant.
4. Confirm settings update on the next invocation and secrets stay out of plain

plugin JSON.

1. Confirm lifecycle events are idempotent and do not create duplicate work.
2. Confirm native controls work by mouse and keyboard, emit the intended named

action, preserve view params, persist correctly, and rerender within limits.

1. Save a source/import change, reopen the palette, and verify hot refresh.
2. Review the diff and run the repository's nearest checks plus git diff --check.

If Termy runtime verification is unavailable, report that gap plainly. Do not call static TypeScript success proof of palette, Worker, tmux, storage, or native GPUI behavior.

Review checklist

• Keep capabilities minimal and manifest/source IDs consistent.
• Keep local imports inside the plugin root; reject dependencies and symlinks.
• Bound selection, input, storage, output, list, network, and subprocess work.
• Keep async pick loaders side-effect free, query-aware, and below option limits.
• Observe context.signal and report useful progress for longer operations.
• Clean up child processes explicitly when cancellation matters.
• Avoid repeated filesystem/network work in render and lifecycle hot paths.
• Use cached/persisted data and small documents; never render an unbounded list.
• Preserve the user's source folder when installing, updating, disabling, or

uninstalling managed copies.

Hand off

State the files changed, declared capabilities, important security/performance decisions, commands run, runtime behavior observed, and any unverified Termy surface.