@extension-use/protocol

The shared language between hosts and clients: message envelopes, error codes, locator and target types, and zod schemas for every built-in action.

npm install @extension-use/protocol

You rarely install it yourself. @extension-use/host and @extension-use/client depend on it, and re-export what you need: ExtensionUseError, ErrorCode, Locator, Target and CallOptions.

Entry points

Import	Contents
@extension-use/protocol	ExtensionUseError, ERROR_CODES, PROTOCOL_VERSION, the envelope types (hello, welcome, call, result, cancel, subscribe, event, progress, bye), Locator, Target, CallOptions, matchPattern()
@extension-use/protocol/schemas	zod schemas for every built-in action (coreActionSchemas) and event (coreEventSchemas), and the CoreActions / CoreEvents type maps
@extension-use/protocol/remote	The frames between an extension and a relay, over one WebSocket

When you'd use it directly

• Writing your own transport or host in another runtime: implement the envelopes.
• Validating action input outside the extension, with the same schemas the router uses.
• Generating docs or tools from the schemas, as pnpm docs:actions does for the action reference.

Errors

import { ExtensionUseError, ERROR_CODES } from "@extension-use/protocol";

const err = new ExtensionUseError("NOT_GRANTED", 'This controller may not call "tabs.close"');
err.code;    // "NOT_GRANTED"
err.message;
err.data;    // optional extra data, e.g. { upgradeUrl } for QUOTA_EXCEEDED
ExtensionUseError.from(unknownError); // wraps anything; unknown errors become INTERNAL

See error codes.