WebMCP Bridge

WebMCP Bridge

Use this skill to operate @webmcp-bridge/local-mcp through one fixed uxc shortcut command per site.

If the target site does not expose native WebMCP and does not already have a fallback adapter, switch to $webmcp-adapter-creator.

Prerequisites

• uxc is installed and available in PATH.
• npx is installed and available in PATH.
• Network access is available for the target website.
• On a fresh machine, or under an isolated HOME, install Playwright browsers first with npx playwright install.
• For local repo development, you may replace the default npx -y @webmcp-bridge/local-mcp launcher with WEBMCP_LOCAL_MCP_COMMAND='node packages/local-mcp/dist/cli.js'.

Core Workflow

1. Identify the bridge source mode before creating any link:
   • Native or polyfill target: use --url .
   • Built-in adapter preset: use --site .
   • Third-party adapter module: use --adapter-module and optionally --url .
2. Pick one stable site name and one site-scoped profile path:
   • default profile root: ~/.uxc/webmcp-profile/
   • never share one profile across different sites
3. Create or refresh the fixed link for that site:
   • command -v -webmcp-cli
   • if the link is missing or the source config changed, run skills/webmcp-bridge/scripts/ensure-links.sh
4. Inspect the bridge and tool schema before calling tools:
   • -webmcp-cli -h
   • -webmcp-cli -h
   • -webmcp-cli field=value
   • -webmcp-cli '{"field":"value"}'
5. Treat presentation mode as explicit runtime state, not command-name intent:
   • check current state with -webmcp-cli bridge.session.status
   • or -webmcp-cli bridge.session.mode.get
   • --headless or --no-headless only sets the preferred default for bridge-managed sessions
   • the actual runtime mode is presentationMode
6. Switch modes explicitly when needed:
   • for normal automation, stay in headless
   • for login, MFA, or human collaboration, run -webmcp-cli bridge.session.mode.set '{"mode":"headed"}'
   • then open or focus the visible session with -webmcp-cli bridge.open
   • if the user manually closes that window, the headed owner session ends; run bridge.open again to start a new headed session on the same profile
   • close the visible owner session with -webmcp-cli bridge.close
7. Parse JSON output only:
   • success path: .ok == true, consume .data
   • failure path: .ok == false, inspect .error.code and .error.message

When Only Bridge Tools Are Visible

If -webmcp-cli -h only shows bridge.* tools, do not keep retrying site tools blindly. The bridge is alive, but the page runtime is not attached to site tools yet.

Use this recovery order:

1. Inspect session state first:
   • -webmcp-cli bridge.session.status
2. If the session is bootstrap-only or auth is incomplete:
   • run -webmcp-cli bridge.session.bootstrap
   • complete login in the browser window
   • then re-run -webmcp-cli -h
3. If a browser/profile already exists but the session is not attached to page tools:
   • run -webmcp-cli bridge.session.attach
   • then re-run -webmcp-cli -h
4. If the task needs a visible browser:
   • run -webmcp-cli bridge.session.mode.set '{"mode":"headed"}'
   • run -webmcp-cli bridge.open
5. Only call site operations after help output shows site tools again.

For auth-sensitive adapter sites such as x and google, seeing only bridge tools during first use is expected until bootstrap or attach completes successfully.

Link Contract

Every site gets one fixed command:

• -webmcp-cli

The link must keep one stable site profile and daemon lock:

• profile path: ~/.uxc/webmcp-profile/
• daemon key: same as profile path

The generated command should default to:

• use --headless
• use --no-auto-login-fallback

This keeps automation deterministic while still allowing runtime switching through:

• bridge.session.mode.get
• bridge.session.mode.set
• bridge.open
• bridge.close

Do not treat one command invocation as a guarantee that the current runtime has already switched. Always inspect presentationMode when mode matters.

Guardrails

• Prefer browser-side execution for privileged site actions. Do not move site credentials into local scripts.
• Do not share one --user-data-dir across multiple unrelated sites.
• Do not dynamically rename link commands at runtime. The skill author chooses the link name once.
• For managed sessions, use bridge.session.mode.set instead of relying on a new launcher invocation to force a mode change.
• For external attach sessions, bridge.session.mode.set is unavailable. Attach to a headed external browser if the task needs a visible window.
• During bootstrap_then_attach, bootstrap is always headed. Do not try to switch mode until attach completes.
• bridge.open and bridge.window.open return UNSUPPORTED_IN_HEADLESS_SESSION when the current runtime is headless.
• For destructive writes, inspect tool help first and require explicit user intent.
• Use --url only for the site the user asked for. Do not silently redirect hosts.

References

• Common creation and invocation patterns:
  • references/usage-patterns.md
• Source mode selection and argument mapping:
  • references/source-modes.md
• Link patterns, naming, and profile layout:
  • references/link-patterns.md
• Common failures and recovery steps:
  • references/troubleshooting.md
• Concrete creation script:
  • scripts/ensure-links.sh