Webmcp Gen

--- name: webmcp-gen description: Create, compile, and validate site-specific WebMCP init scripts from a target URL and desired tool capability. Use when the user wants to author WebMCP tools for a website, produce a webmcp.init.js artifact, or test WebMCP registration and invocation through Stagehand. compatibility: "Requires Node 18+ and Chrome/Chromium with WebMCP testing flags. Run `pnpm install` in the skill directory to install the Stagehand dependency. Page exploration uses the browse CLI (`npm install -g browse`)." license: MIT allowed-tools: Bash Read Grep Edit Write --- # WebMCP Gen Author website-specific WebMCP tools by writing a manifest, compiling it to an init script, and validating that Chrome registers and invokes the tools. This skill does not call a nested agent. You are responsible for exploring the page, writing `manifest.json`, and iterating based on validation output. ## Setup check From the skill directory, install dependencies if they are not already installed: ```bash cd skills/webmcp-gen pnpm install ``` This installs the pinned Stagehand package plus the TypeScript toolchain (`tsx`, `typescript`, `@types/node`) used to run the generated `stagehand-example.ts`. ## Workflow 1. Pick an artifact slug with exactly one slash: ```text / ``` Example: ```text example.com/page-context ``` 2. Scaffold the artifact: ```bash node scripts/scaffold.mjs example.com/page-context --url https://example.com ``` 3. Explore the target page with the `browse` CLI: ```bash browse open https://example.com --local browse snapshot browse get title browse get url browse get text body browse get html body ``` Prefer `browse snapshot`, page text, and DOM inspection over screenshots unless visual layout matters. Use `browse stop` when exploration is complete. 4. Edit `artifacts///manifest.json`. The manifest is the source of truth. 5. Compile: ```bash node scripts/compile.mjs artifacts/example.com/page-context ``` 6. Generate a runnable Stagehand example (`stagehand-example.ts`) and run it with `tsx`: ```bash node scripts/generate-stagehand-example.mjs artifacts/example.com/page-context npx tsx artifacts/example.com/page-context/stagehand-example.ts ``` 7. Validate: ```bash node scripts/validate.mjs artifacts/example.com/page-context ``` 8. If validation fails, inspect `eval.json` and `eval-report.md`, patch `manifest.json`, then compile and validate again. ## Manifest contract ```json { "domain": "example.com", "task": "page-context", "url": "https://example.com", "generatedAt": "2026-06-04T00:00:00.000Z", "tools": [ { "name": "example_com_page_context", "description": "Returns page context.", "inputSchema": { "type": "object", "properties": {}, "required": [] }, "implementation": { "kind": "dom", "source": "return { success: true, title: document.title, url: location.href };" }, "fixtureInput": {} } ] } ``` ## Authoring rules - `implementation.source` is inserted inside `async (input) => { ... }`; write JavaScript statements, not a full function wrapper. - Return a JSON-serializable object. - WebMCP code runs inside the browser page. Use browser-native APIs: `document`, `location`, `navigator`, and same-origin `fetch`. - Do not use Playwright, Puppeteer, Stagehand, XPath helpers, or agent/browser commands inside `implementation.source`. - `document.querySelector` and `querySelectorAll` must receive valid browser CSS selectors only. - To find visible text, use `Array.from(document.querySelectorAll(...)).find((el) => (el.textContent || "").includes("..."))`. - Do not include API keys, bearer tokens, cookies, localStorage secrets, or user credentials. - Do not use `eval` or `new Function`. - Avoid destructive actions unless the user explicitly asked for them. - Make implementations defensive: check for missing elements and return structured `{ success: false, error: "..." }` responses. - Generated init scripts register WebMCP tools only in the top frame. ## Output layout ```text artifacts/// manifest.json webmcp.init.js stagehand-example.ts eval.json eval-report.md ``` To turn the example into a standalone project, scaffold a Stagehand app with `npx create-browser-app` and drop the generated `webmcp.init.js` into it (load it with `page.addInitScript({ path: "webmcp.init.js" })`).