Use one part or all four.

ui
A panel, drawn natively

A sandboxed Bun worker describes views with signals and components; the app draws them with its own renderer. It has no network.
main
The part that does things

Bun under a Seatbelt profile built from what it declares: which commands, hosts, files and environment it may use. The panel reaches it through a typed contract.
helpers
Native when it must be

Signed programs pinned to their Apple team ID at install, for work like streaming a simulator or a web page into a live surface.
agent
Tools and skills for agents

Served to Claude Code, Codex and Pi through the plugin gateway, with hooks before and after tool calls.

Twenty lines to a native panel.

This is the hello example. The view function runs again whenever the session or its state changes, and the app redraws only what changed.

hello/src/ui.ts

import { defineExtension, ExtensionIdSchema, space } from "@napdock/extensions";export default defineExtension({  id: ExtensionIdSchema.make("hello"),  title: "Hello",  setup(api) {    let clicks = 0;    // Runs again whenever the session or the state changes.    api.view((ui, { session }) => {      ui.column({ gap: space["3"], padding: space["4"] }, () => {        ui.heading("Hello from an installed extension");        ui.text(`${String(session?.turns.length ?? 0)} turns so far`, { color: "muted" });        ui.button(clicks === 0 ? "Click me" : `Clicked ${String(clicks)}`, {          onClick: () => { clicks++; },        });      });    });  },});

The hello example installed and open in a side pane: Hello from an installed extension, the workspace and its turns, and a Click me button.

The panel asks. Main does. Types check both.

The panel can't reach the network; its main part can, but only the hosts it declared. They talk through a contract defined once with Effect Schema, so a wrong shape fails in your editor, not in front of a user.

repo-stars/src/contract.ts

import { Schema } from "effect";import { Ipc } from "@napdock/extensions/ipc";// Owner, Repo and RepoError are Effect schemas defined above./** What the panel asks of `main`, typed on both sides. */export const Repos = Ipc.define({  name: "repos",  methods: {    top: {      input: Schema.Struct({ owner: Owner }),      output: Schema.Array(Repo).check(Schema.isMaxLength(10)),      error: RepoError,    },  },  state: Schema.Struct({    served: Schema.Int,    lastOwner: Schema.NullOr(Schema.String),  }),});

Anywhere the app draws.

An extension at work: a test run drawn by the Workbench example's tool renderer, and its count in the status bar.

Panel: A pane beside the session, with tabs and its own scope
Command: In the palette, on a key, or as a slash command
Settings page: Under Settings → Extensions
Slots: Title bar, status bar, composer pill, session header, sidebar and message actions
Tool renderer: Draw a tool call your way, such as a test run
Markdown renderer: Render a fenced block, such as csv
File viewer: Open a file type the app doesn't know
Link handler: Decide what a pasted or clicked link opens
Dialogs and toasts: Ask, confirm, and offer actions
Themes and keys: Ship a theme or a keybinding

A host API, not a back door.

Extensions work through the app: they ask it to insert into the composer, open a pane or call a service, and the app decides whether they may.

Composer: Insert text, set it, attach a file, choose a model
Layout: Open, focus and size panes
Stores: Global and per-session state that persists
Connections: Call a service, including GitHub, with an account the user granted; the token never reaches the extension
Contracts: Share typed interfaces with other extensions
Agent hooks: Before and after a tool, on a prompt, on a permission request

Scaffold, test, link, ship.

napdock-ext writes a package from a template (panel, command, tool or webview), tests it against a fake app, links it to the running app with reload on save, and packs a reproducible archive.

my-panel

$ napdock-ext new my-panel --template panelnapdock-ext new my-panel --template panel$ cd my-panel && napdock-ext testcd my-panel && napdock-ext test$ napdock-ext devnapdock-ext devWatching /Users/me/my-panel; press Ctrl-C to stop.Built dist/ui.js (ui, 1.0 KB)Linked my-panel 0.1.0, revision 1: the app installs it and reloads it.

Six to start from.

Examples you add from a folder in Settings → Extensions. The app itself ships with none, so what you install is what you get.

The Browser preview example extension in a side pane, showing a local dev server, with Screenshot to composer.

GitHub

Every pull request and issue of the project: an inbox sorted by what needs you, native review with viewed marks and threads, stacks, checks and merging, and Work on this PR to start a session on its branch.
iOS Simulator

The simulators on this Mac in tabs or side by side, with Home, rotate, recording into the composer, and tools agents use to read the screen and tap elements.
Browser preview

Your dev server rendered off screen and streamed into a live surface that takes clicks, scrolling and typing, with Screenshot to composer.
Repo stars

A panel that asks its main part, through a typed contract, for an owner's most starred repositories.
Workbench

Every contribution point at once: a command, a settings page, a status bar slot and renderers.
Hello

The smallest extension: what is selected, and a counter.

Small enough to trust.

Bundle: 4 MB per entry
Package: 4,096 files and 64 MB
Install from: A folder, a packed archive or npm, without install scripts
Integrity: A SHA-256 hash for every file
Permissions: Off until granted; revoke any of them in Settings