Idea Board - Imperative WebMCP API Playground

Tool definition

Properties of tool in document.modelContext.registerTool(tool, options).

nameString

Identifies the tool. Must be unique. Letters, digits, hyphens, underscores, and dots; maximum 128 characters.

descriptionString

Describes what the tool does. Helps the agent decide when and how to use it.

inputSchemaObject

Describes the accepted input parameters. Uses JSON Schema.

executeFunction

Handles invocation and returns the result to the agent. Can be sync or async. Receives the input object and an options object whose signal is aborted when the invocation is canceled.

titleString, optional

Provides a friendly display name for UIs. The agent still uses name for invocation.

annotationsObject, optional

Provides hints about tool behavior.

• readOnlyHint: true: does not mutate state.
• untrustedContentHint: true: output may contain untrusted content.
• consequentialHint: true: action has significant consequences, such as making a payment.

Omitted hints default to false when an annotations object is supplied.

Input validation: Chromium does not validate inputs against inputSchema. Validate them in execute.

Registration lifetime

options.signalAbortSignal, optional

Removes the tool registration when aborted. Create an AbortController and pass controller.signal to registerTool(). Call controller.abort() to unregister the tool at any time. This controls registration lifetime, not the invocation cancellation signal received by execute.

Discovery and exposure

getTools(options?)document.modelContext method

Discovers tools available to the calling document. Returns a Promise<RegisteredTool[]>.

fromOriginsArray<String>, optional

Includes tools from the listed origins. An option for getTools(). Tools must be exposed to the calling document and are included alongside same-origin tools. An omitted or empty list returns only same-origin tools.

exposedToArray<String>, optional

Shares a tool with the listed origins. An option for registerTool(). Allows a cross-origin iframe to expose its tool to its parent document.