WebMCP & browser agents

Some agents don't just fetch your pages — they operate them: WebMCP clients calling navigator.modelContext, and browser agents clicking and typing through your UI. The browser SDK detects them in the page and upgrades them to a verified identity when they present a credential.

Install

npm install @agentronics/sdk

import { Agentronics } from '@agentronics/sdk'
 
const client = Agentronics.init({
  publishableKey: process.env.NEXT_PUBLIC_AGENTRONICS_KEY!, // agtx_pk_… — never a secret key
  siteId: 'shop-acme-com',
})
 
const identity = await client.detect()
// → { class: 'webmcp', trust: 'detected', vendor: …, confidence: 1, … } or null

Passing a secret key (agtx_sk_…) throws at init(), so a leak fails loudly. React? Use <AgentronicsProvider> from @agentronics/react — see Next.js.

From detected to verified

client.detect() always returns the highest-trust identity available.

Verifying credentials

A browser can't safely verify a credential by itself, so authenticate() hands tokens to a verifyToken hook that calls your server (which can use the Agentronics gateway or your own logic):

const client = Agentronics.init({
  publishableKey: process.env.NEXT_PUBLIC_AGENTRONICS_KEY!,
  auth: {
    verifyToken: async (method, token) => {
      const res = await fetch('/api/agent/verify', {
        method: 'POST',
        headers: { 'content-type': 'application/json' },
        body: JSON.stringify({ method, token }),
      })
      return res.ok ? res.json() : null // a VerificationResult, or null
    },
  },
})
 
await client.authenticate({ bearerToken: 'agt_bearer_…', vendorHint: 'claude', classHint: 'webmcp' })

Supported inputs: bearerToken, extensionToken, oauth2AccessToken, ssoIdToken, spiffeJwt, xfccHeader, sessionLinkToken (+ linkedUserId), xAgentHeader and a declaration. SSO, SPIFFE and mTLS are verified by the gateway — see SSO, SPIFFE and mTLS.

Handing back to a human

When an agent returns control to a person, call client.clearIdentity().

What detection can and can't see

• WebMCP — exact when an agent uses navigator.modelContext.
• DOM drivers (Playwright-style automation) — heuristic, with a confidence score.
• Screenshot agents (pixel-level control) — not reliably detectable; they should authenticate if they need more than anonymous access.

Pair the browser SDK with the server middleware: the server sees every request, the browser sees what happens on the page.