Speakable WebMCP Manifest v1.0

The gap this closes

W3C WebMCP lets web pages expose capabilities to AI agents via two complementary APIs: window.navigator.modelContext.registerTool(tool, { signal }) for JavaScript registration, or declarative HTML form annotations — <form toolname="..." tooldescription="..."> — that the browser auto-wires without any JS. Chrome Early Preview (flag-gated as of Apr 24, 2026) is the reference runtime. The Draft Community Group Report explicitly lists "Enable/influence discoverability of sites to agents" as a non-goal. That means: agents don't know, pre-page-load, what tools a site will register, what permissions they need, or whether the site operator actually authored them.

Speakable's manifest closes that gap with four guarantees:

• Declaration — tools are listed at a well-known URL before any page runs.
• Authenticity — Ed25519-signed inventory, verifiable against the site's Web Bot Auth key directory.
• Risk classification — every tool carries a riskClass (read, mutate, transact, escalate).
• Drift detection — agents reconcile runtime registrations with the manifest and halve trust on mismatch.

Canonical location

https://{domain}/.well-known/webmcp.json

Sites MAY also link the manifest from the document head: <link rel="webmcp-manifest" href="/.well-known/webmcp.json">

Specification

The authoritative spec — schema, risk classes, signature flow, drift rules, and migration plan for when the W3C draft ships its own discoverability format — lives in the repo at certification/spec/webmcp-manifest-v1.md.

• Speakable's own signed manifest (dogfooded at getspeakable.ai)
• Speakable Trust Certificate — includes the platform's WebMCP cert summary block
• W3C WebMCP upstream proposal

Integration with the Speakable scoring rubric

• Discoverability (Pillar 1) — 0–10 points in Technical Discovery for manifest presence, signing, tool coverage, and runtime parity.
• Verification (Pillar 2) — a signed manifest (or explicit empty manifest) is required for the Enhanced and Full agent-identity tiers.
• Transactability (Pillar 3) — 0–7 points for the transact tool ladder (read → mutate → transact with requiresUserInteraction enforcement and UCP continue_url fallback).
• Certification (Pillar 4) — the Certified tier requires a signed manifest with no runtime drift.