Imported from imbue-ai/sculptor (sculptor/sculptor-plugin/skills/build-sculptor-extension/SKILL.md). Install upstream with npx skills add imbue-ai/sculptor --skill build-sculptor-extension. Copyright stays with the author.

Build a Sculptor extension

An extension is a runtime ES module the Sculptor frontend imports at load time. It is not built into the app — it ships as its own files and is loaded live. Everything you need is in this file plus the sculpt CLI; you do not need the Sculptor source code or a dev build of Sculptor (see the last section for when they help).

An extension is a directory containing manifest.json plus an ESM entry module that default-exports an activate(api) function.

Two files ship next to this SKILL.md (resolve them against this skill's base directory):

• sdk.d.ts — the authoritative, generated contract of @sculptor/extension-sdk: every hook, component, and registration option with its doc comments. Read it before writing extension code; the prose below only summarizes it.
• example/ — the quick-start extension below as ready-to-load files (Sculptor's e2e tests load this exact directory, so it is known-good).

Quick start (no build step)

// manifest.json
{ "id": "hello", "name": "Hello", "version": "0.1.0", "entry": "main.js", "sdkVersion": "^1.0.0" }

// main.js — hand-written ESM, imported directly by the host (no bundler)
export default function activate(api) {
  const el = document.createElement("div");
  el.textContent = "hello from an extension";
  el.style.cssText = "position:fixed;bottom:16px;right:16px;pointer-events:auto;";
  document.body.appendChild(el);
  return () => el.remove(); // disposer — REQUIRED cleanup on unload/reload
}

sculpt extension load <this-skill's-base-dir>/example   # package + load into the live UI
sculpt extension inspect hello                          # see what it registered

Prerequisites — the two settings toggles

Both live in Settings → Extensions in the Sculptor UI; only the user can flip them:

• Extensions (enable_extensions, default on) — master switch for the extension runtime.
• Agent extension loading (allow_agent_extension_loading, default off) — gates the mutating CLI ops (load, reload, unload, remove). Read-only ops (list, inspect, dir) always work.

If a mutating command fails with HTTP 403 / agent_extension_loading_disabled, ask the user to enable "Agent extension loading" under Settings → Extensions, then retry. If no window responds at all, Sculptor isn't running or extensions are disabled.

Dev loop — sculpt extension

(See the sculpt-cli skill for general sculpt usage; all commands accept --json and infer the workspace from SCULPT_WORKSPACE_ID.)

load mechanics worth knowing:

• A local path is packaged and uploaded (dotfiles, node_modules, and __pycache__ are skipped; 5 MB encoded limit) to a workspace-scoped dev install at <extensions-dir>/dev/<workspace-id>/<extension-id>/. Re-loading wipes and rewrites that directory.
• --persist installs to the top-level <extensions-dir>/<extension-id>/ instead — a permanent install that survives after this workspace is gone. URLs are always persistent sources; --persist has no effect on them.
• The extension id must be a single safe path segment: no / or \, not exactly . or .. (dots inside an id like foo.bar are fine), and not the reserved name dev.
• load and reload wait for the extension to settle: load: OK means it reached status: loaded (manifest fetched, validated, imported, activated). A failure at any phase (manifest, validate, import, activate, or the catch-all load) prints load: FAILED with the phase and error message and exits non-zero. Errors thrown after activation (e.g. inside a component render) surface in the UI's per-extension error boundary instead — check inspect and the UI when something registered but doesn't render.

Typical loop: load → edit → load again → … → remove (cleanup) or load --persist (keep it installed). Do not reach for reload in this loop — it re-imports the previously uploaded copy, so your edits won't show up.

Manual no-CLI route: drop the extension directory into <extensions-dir>/<extension-id>/ (path from sculpt extension dir) and click the Refresh button in Settings → Extensions.

manifest.json

All five fields are required non-empty strings; there are no optional fields:

The entry module — activate and disposers

type ExtensionActivate = (api: ExtensionHostApi) => void | (() => void) | Promise<void | (() => void)>;

• The host imports the entry and calls its default export with the API.
• Return a disposer that undoes every module-level side effect (DOM nodes, event listeners, timers, injected <style> tags). Disposers must be synchronous. Registrations made through api.register* each return their own undo function — compose them into the disposer you return.
• If activate throws or rejects, the extension lands in error status with phase activate, any registrations it already made are rolled back, and other extensions are unaffected.
• On reload the disposer runs, then the module is re-imported (cache-busted) and re-activated.

The host API and SDK — read sdk.d.ts

The full typed contract — ExtensionHostApi, every registration option shape, every hook signature, and their doc comments — is in the generated sdk.d.ts next to this file. It is authoritative; read it rather than trusting any summary. What it contains, in one breath:

• api.registerPanel / registerSettings / registerOverlay / registerWorkspaceWidget / registerHomeView — each returns an undo function; registering twice with the same id replaces the previous contribution; every component renders inside a per-extension error boundary and receives no props.
• Hooks: useCurrentWorkspace (selector form available), useWorkspaces, useWorkspaceTasks, useNavigateToWorkspace, useOpenNewWorkspaceModal, useExtensionSetting, useExtensionSettings, useSetExtensionSetting.
• Components and actions: Markdown, PanelHeader, openExternal.

Semantics that matter beyond the types:

• Workspace scope: panels and workspace widgets are mounted per-workspace, so workspace-scoped hooks work directly. Overlays, home views, and settings components are app-global — useWorkspaceTasks is unavailable there, and useCurrentWorkspace reflects whichever workspace the current route shows (or null).
• Overlays render in a pointer-events: none layer — interactive elements must set pointer-events: auto themselves.
• useExtensionSetting persists per-extension strings in localStorage (sculptor-extension:<id>:<key>). Values are plaintext — treat anything the user puts there (e.g. an API token) as visible to anyone with devtools access, and JSON-encode yourself if you need structure.
• Prefer the selector form of useCurrentWorkspace (e.g. (w) => w?.branch ?? null) to avoid re-rendering on unrelated workspace changes.

Host-provided modules — never bundle these

The host import map provides exactly these bare specifiers; mark them as externals in any build, and never ship your own copy (a second React instance breaks hooks):

react   react/jsx-runtime   react-dom   react-dom/client
jotai   @tanstack/react-query   @radix-ui/themes   lucide-react
@sculptor/extension-sdk

Notes: @tanstack/react-query deliberately does not expose QueryClient / QueryClientProvider — extensions share the host's query cache; namespace your query keys with your extension id (e.g. ["my-extension", "issue", id]). Importing a name a module doesn't export silently yields undefined at runtime, so verify in the UI rather than trusting the build.

Two flavors: no-build vs. built

No-build (start here): hand-written ESM. Raw DOM (as in the quick start), or React without JSX via createElement:

import { createElement as h, useState } from "react";
import { useExtensionSetting } from "@sculptor/extension-sdk";

const Badge = () => {
  const [label, setLabel] = useExtensionSetting("label");
  return h("div", { style: { pointerEvents: "auto", position: "fixed", top: 8, right: 8 } },
    h("input", { value: label, onChange: (e) => setLabel(e.target.value) }));
};

export default function activate(api) {
  return api.registerOverlay({ id: "badge", component: Badge });
}

Built (when you want JSX/TypeScript/dependencies): any bundler that emits a single ESM file with the host modules external. Minimal Vite setup:

// vite.config.ts — devDependencies: vite, @vitejs/plugin-react
import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";

export default defineConfig({
  plugins: [react()],
  define: { "process.env.NODE_ENV": JSON.stringify("production") },
  build: {
    lib: { entry: "src/index.tsx", formats: ["es"], fileName: () => "main.js" },
    rollupOptions: {
      external: [
        "react", "react/jsx-runtime", "react-dom", "react-dom/client",
        "jotai", "@tanstack/react-query", "@radix-ui/themes", "lucide-react",
        "@sculptor/extension-sdk",
      ],
    },
  },
});

The SDK is not published to npm. For TypeScript, copy the sdk.d.ts shipped next to this skill into your project and alias it in tsconfig.json: "paths": { "@sculptor/extension-sdk": ["./sdk.d.ts"] } (you'll want @types/react installed for full fidelity). After building, place manifest.json next to the bundle ("entry": "main.js") and sculpt extension load <dist-dir> — loading the output directory keeps the upload small.

Gotchas

• load/reload report the settled status, but errors thrown after activation (event handlers, component renders) don't reach the CLI — when something registered but misbehaves, check inspect and the UI's per-extension error boundary.
• Disposers are synchronous; clean up injected styles/listeners/timers, not just DOM nodes.
• Overlays: remember pointer-events: auto on interactive elements.
• Settings are plaintext localStorage; inspect reports key names only.
• Use Radix theme CSS variables (e.g. var(--gray-12), var(--accent-9)) so the extension follows the host theme, and @radix-ui/themes components for native-feeling UI.
• One extension id wins per source priority (local > url > builtin); a shadowed duplicate loads its manifest but never activates.

Going deeper with the Sculptor source (optional)

None of this is required — the contract above is complete — but if you have a checkout of github.com/imbue-ai/sculptor (or are already working in it), you can go deeper:

• SDK source: sculptor/frontend/src/extensions/types.ts (host API contract) and sculptor/frontend/src/extensions/sdk/ (hooks, components, actions) — the sdk.d.ts next to this skill is generated from these (just generate-extension-sdk-dts).
• Reference extensions: sculptor/frontend/public/extensions/sculpty/ (no-build raw DOM), sculptor/frontend/public/extensions/pomodoro/ (no-build React overlay with persisted settings), and sculptor/frontend/extensions/linear-issue/ (full TypeScript/Vite panel + settings + widget + home view).
• Bundled extensions: extensions shipped with the app are built by the host's Vite config (sculptor/frontend/vite-plugins/bundled-extensions.ts); adding an id to COMPILED_EXTENSION_IDS there builds extensions/<id>/src/ automatically.
• In-repo skills: when working inside the Sculptor repo you can run a dev build of the app and use the auto-qa-changes skill to drive the UI in a headless browser for visual verification, instead of relying on the user's live instance.