webToolSignature

Returns a string of what WebMCP sees of a tool.

Returns a string of what WebMCP sees of a tool. When it changes, the tool must re-register; when it does not, it must not, because Chrome cancels the calls of a tool whose definition changes. Reach for it when you build your own registration on top of registerWebTool.

Import

import { webToolSignature } from "@webmcp-agents/core";

Example

Re-register a tool only when the definition the agent sees changed.

import { type WebTool, webToolSignature } from "@webmcp-agents/core";

let registered: string | undefined;

/** Re-register only when what the agent sees changed. */
export function needsReregistration(next: WebTool): boolean {
  const signature = webToolSignature(next);
  const changed = signature !== registered;
  registered = signature;
  return changed;
}

Options

webToolSignature(tool).

Name	Type	Default	Description
`tool`	`WebTool`	required	The tool to describe, made with `defineWebTool`.

Returns

A string: JSON.stringify of [id, title, description, jsonSchema, annotations ?? null, !!requireConfirmation, target ?? null], where annotations are the merged hints (the tool’s annotations with its flags written over them), so changing a flag changes the signature.

Notes

execute is not part of the signature: a new execute alone needs no re-registration. Neither are match, fill or fields: a registered tool reads them from its latest definition on every call.
A locator or selector target is part of the signature. A function target stringifies to null, so swapping one function target for another does not change the signature (the new one is read on the next call).
createToolRegistry uses it in update(catalog), and useWebTool uses it to decide when to re-register.