Agent Verification Utility

Deterministic JSON checks with signed evidence and x402-paid execution

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Documentation

MCP and x402 Interoperability

A machine-first purchase flow that keeps discovery and quoting free while charging only for deterministic execution.

Public MCP transport

The stateless Streamable HTTP endpoint is https://agent-economy.kgninja.dev/mcp. A client can call tools/list without authentication. The free tools are describe_verify_evidence, get_revenue_goal_status, quote_verify_evidence, and prepare_verify_evidence_purchase. The paid tool is verify_evidence.

Paid tool sequence

  1. POST { request, spend_policy } to the free precheck and copy its receipt digest into the paid intent.
  2. Call verify_evidence with a unique idempotency key and that complete intent.
  3. An unpaid call returns an MCP tool error whose _meta["x402/error"] contains an x402 v2 PaymentRequired document and a paid verification binding.
  4. Validate the precheck hash, binding digest, price cap, policy version, evidence digest, quote expiry, scheme, CAIP-2 network, asset, amount, and receiving address against local policy.
  5. Sign a supported requirement with an x402-capable client only when every field still matches.
  6. Retry the identical tool call with the encoded payment in _meta["x402/payment"].
  7. Preserve _meta["x402/payment-response"], the delivered binding with paid receipt ID, and the signed evidence.

The HTTP route https://agent-economy.kgninja.dev/verify-evidence can create its own bound quote only from a complete paid intent and return PAYMENT-REQUIRED directly; empty or raw-request probes fail before a quote or payment requirement is created. Calling https://agent-economy.kgninja.dev/quote first remains available for explicit economic preflight. Both modes use equivalent PAYMENT-SIGNATURE and PAYMENT-RESPONSE headers and require the same binding digest.

Discovery surfaces

The x402 Bazaar extension is present in live payment requirements. Bazaar indexing is controlled by the ecosystem facilitator and occurs only after a successful settled payment; publishing metadata alone is not a claim that indexing has occurred.

A2A quote preparation

The A2A 1.0 JSON-RPC endpoint implements synchronous SendMessage. Send Content-Type: application/json and A2A-Version: 1.0, with exactly one structured data part containing idempotency_key and the same paid intent used by HTTP or MCP. Repeating the same idempotency key and intent reuses the quote. The response is a direct agent Message containing the validated bound quote and exact purchase instructions. It does not authorize payment or execute paid work; the calling agent must independently evaluate and satisfy the later x402 challenge.

This adapter deliberately creates no A2A Task records. ListTasks therefore returns an empty collection, while GetTask, CancelTask, and a SendMessage containing taskId return TaskNotFoundError. Streaming, push notifications, and extended Agent Cards are declared unsupported and return the corresponding A2A capability errors instead of pretending those features exist.

Browser agents

The landing page loads a same-origin, feature-detected WebMCP bridge. In browsers that expose document.modelContext or navigator.modelContext, it maps the live MCP tools/list result to browser tools and proxies calls back to the same MCP endpoint. In other browsers it is a safe no-op.

Machine-readable references