webmcp-gen

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellDeclared1 observation
• DependenciesNot pinnedSome versions float
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

if (implementationSource.includes("eval(") || implementationSource.includes("new Function")) {

@types/node, tsx, typescript

Audit 0.4.1 · source sha 45d21dc75974 · 31 Oct 2026Report an issue or request a re-scan

• Publisherbrowserbase GitHub organizationOwner of the repository this skill is read from
• Source folderbrowserbase/skills/skills/webmcp-genThe exact folder we audited
• LicenceNot declaredAs the repository states it
• Commit pinned for this verdict45d21dc75974A new audit runs when the source changes
• Repository statusNot archivedLast push 3 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its 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…

---
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
<domain>/<task>
```

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/<domain>/<task>/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/<domain>/<task>/
  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" })`).

Excerpt, first 4,439 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/browserbase/skills
git -C skills checkout 45d21dc75974

Works in

1. 2026-10-31
   ✕BLOCK D 69 / 100

   first audit · source 45d21dc75974

Questions about webmcp-gen

• github.com/browserbase/skills/tree/main/skills/webmcp-gen — the audited source at commit 45d21dc75974 and every finding aboveObserved · 31 Oct 2026

Spotted something wrong? Report a correction · Methodology