Registered tools are the specific capabilities (like "Book a Table" or "Add to Cart") that your website exposes to AI agents.
How the Registered WebMCP tools audit works
This audit is informational. Lighthouse lists all WebMCP tools registered on the page using the Declarative or Imperative APIs. If no tools are registered, the result list will be empty.
Lighthouse issues a warning when more than 40 tools are registered. By including a high excess of tools, you are likely to consume model context tokens, add latency, and increase the risk of confusion for agents as to what tool to use.
How to fix
You can register tools using either the Declarative API or the Imperative API:
- Declarative API: Add
toolnameandtooldescriptionattributes directly to your<form>elements. - Imperative API: Use JavaScript to register tools using
document.modelContext.registerTool.
Best practices
- Use clear, action-oriented names (for example,
toolname="book_appointment"). - Provide detailed descriptions that explain what the tool does and when an agent should use it.
- Avoid registering more than 40 tools at once. Register tools only when they're useful for the current page state, and unregister them when they're no longer needed.
- If you want to learn more, read the WebMCP documentation.