Agent Runtime

A manifest tells an agent what a page can do. The runtime tells it what the page can do right now — which actions are on screen, enabled, and permitted for this user.

npm install @axag/webmcp

Registration follows the UI

import { registerManifest } from '@axag/webmcp';
import { tools } from 'virtual:axag/tools';

const route = new AbortController();
registerManifest(tools, { signal: route.signal, handlers });

// Leaving the route takes its tools with it.
route.abort();

The AbortSignal is the whole lifecycle: WebMCP has no unregisterTool, and aborting the signal you registered with is how a tool goes away. Tie that signal to whatever owns the action — a component, a route, a dialog — and the agent's list can't drift from the screen.

Why not register everything at startup

The earlier provideContext() call was removed from the specification in March 2026 because it encouraged registering every tool up front, leaving ghost tools pointing at UI that had since unmounted. Registration scoped to a signal is the replacement.

Visibility and operability

AXAG distinguishes visibility from operability. The runtime enforces it: an action is unregistered while its element is

• disabled (including through a disabled <fieldset>),
• hidden, inert, aria-hidden="true" or aria-disabled="true",
• or no longer in the document,

and registered again when the element becomes operable. One MutationObserver serves every registration on the page.

This is what keeps an agent from being offered a button a person couldn't press.

Executing an action

Without a handler, the runtime does what a person would: it fills the form the annotation points at using the tool's arguments, then presses the control.

• Parameters are matched by the name in the manifest, so display_name finds displayName.
• Values are assigned through the prototype setter, so React and Vue notice the change.
• Checkboxes, radio groups and multi-selects are set by value.

Pass a handler to call your own code instead.

Middleware

registerManifest(tools, {
  signal: route.signal,
  middleware: [requireConfirmation, withTenantScope, auditLog],
});

Middleware wraps every invocation, in order, and can refuse the call. Safety enforcement belongs here rather than inside each handler.

Client-side checks are not enforcement

An agent running in the page can call your API directly. Middleware improves what the agent does; the server still has to enforce confirmation, approval and tenant boundaries.

Pages without a build step

import { registerDocument } from '@axag/webmcp';
registerDocument({ signal: controller.signal });

Reads the annotated elements on the page, harvesting parameters from their forms. Costs a DOM scan; prefer registerManifest with build-time tools where you have a bundler.

Browser support

The runtime uses document.modelContext, falling back to navigator.modelContext (deprecated in Chromium 150). Where neither exists, registration reports through onError instead of throwing, so a page that annotates for agents still works for people.

Framework bindings

Framework	Package	Reach for
React	@axag/react	useAxag, <AxagAction>
Vue	@axag/vue	useAxag, v-axag
Angular	@axag/angular	[axag] directive