MCP x402 – Evidence Backed Web Verification

What MCP x402 – Evidence-Backed Web Verification does

MCP x402 – Evidence-Backed Web Verification evaluates information published on a public web page. An agent supplies an HTTP(S) URL and between one and ten concrete conditions, such as whether a seller is identified, a product is available in Portugal, a price is shown in euros, or a policy mentions a required service.

The result is reported per condition using three possible decisions: confirmado when the page clearly supports the condition, rejeitado when it clearly contradicts it, and incerto when the available page evidence is insufficient. Results include the final source URL, page title, verification time, an explanation for each condition, quoted proof when available, a unique verificationId, and a SHA-256 pageHash.

How it works

The service can be reached through its public MCP endpoint or HTTP endpoints. Paid verification uses x402 version 2 payments on Base mainnet, identified by eip155:8453, with a listed price of $0.05 USDC per verification. A free preflight route validates the request before payment. The repository also includes a buyer that connects to the live service, checks the payment requirements against Base mainnet USDC and the maximum amount, signs the payment, retries the same call, and prints the settlement receipt and result.

The production service is deployed on Railway. Its public MCP endpoint is https://mcp-x402-production.up.railway.app/mcp; the service also exposes health, preflight, URL analysis, and paid verification routes. Bazaar discovery metadata is enabled on the paid HTTP and MCP surfaces.

MCP x402 – Evidence-Backed Web Verification is most relevant to procurement agents, seller and offer checks, pre-purchase due diligence, policy validation, and other workflows that require evidence before an action. It only evaluates evidence extracted from the supplied public page, so it is not a substitute for checking private systems or inaccessible sources.

Setup and configuration

For local server development, the repository documents npm install, npm run dev, npm run build, and npm start. The server requires OPENAI_API_KEY; OPENAI_MODEL is optional and defaults to gpt-5-mini. HOST and PORT are optional, with documented defaults of 0.0.0.0 and 3000. PUBLIC_SERVICE_URL can define the canonical public HTTPS origin, while Railway can supply RAILWAY_PUBLIC_DOMAIN automatically. OBSERVABILITY_SALT is recommended for pseudonymizing source and client fingerprints across restarts.

The included local buyer has separate wallet configuration. EVM_PRIVATE_KEY is required for the buyer to authorize Base mainnet payments, and JOURNEY_ID is optional. The private key should not be committed or exposed. Running the buyer commands can authorize real payments.

Tools and capabilities

• verificar_condicoes: verifies one or more conditions against a public page for $0.05 USDC.
• analisar_url: fetches and analyzes a public HTTP or HTTPS page for $0.05 USDC.
• consultar_ia: sends a prompt to the OpenAI Responses API for $0.02 USDC.
• HTTP access through /analyze and /verify-conditions.
• Free health and preflight routes for service or request validation.
• Evidence metadata including source URL, title, timestamp, quoted proof, verification ID, and page hash.

Limitations and notes

The verification input must be a public HTTP(S) page, and the conditions should be concrete. A page that does not contain enough evidence produces incerto; the system does not establish a condition merely because the page is relevant. Paid calls require USDC on Base mainnet, while local server execution requires an OpenAI project API key. Rate limiting is documented at 100 requests per 15 minutes.