OnchainDiligence — MCP Server

A paid, non-custodial Model Context Protocol server that exposes on-chain compliance checks as tools AI agents can discover and pay for autonomously. Sanctions screening and UK company verification, billed per call in USDC on Base via the x402 protocol — no API keys, no accounts, no subscriptions.

Live at `https://mcp.onchaindiligence.com/mcp` · Listed in the official MCP Registry as com.onchaindiligence/compliance · Part of onchaindiligence.com.

What it does

An agent connects over Streamable HTTP and finds three tools:

Each result is the same factual data the HTTP API returns — the check logic is shared byte-for-byte, so an agent calling via MCP gets results identical to one calling over HTTP.

How payment works

Payment rides on x402, the open agent-payment standard built on HTTP 402 Payment Required:

1. The agent calls a tool with no payment attached.
2. The server returns the payment requirements (amount, asset, recipient, network).
3. The agent signs a USDC payment authorization from its own wallet.
4. The agent retries the call with the payment in the tool-call _meta.
5. The server verifies and settles via the Coinbase facilitator, runs the check, and returns the result.

The flow is non-custodial: USDC moves directly from the agent's wallet to the recipient. This server never holds funds and runs no billing system — which is deliberate, given the product is about not being a trusted intermediary.

Two payment rails by design

OnchainDiligence settles two ways, because the agent-payment landscape is split between two standards:

Same checks, same signed results, different rails for different ecosystems.

Architecture

agent (MCP client + x402 wallet)
      │  Streamable HTTP
      ▼
index.ts ──────────── Hono app, routes /mcp to the handler
      ▼
src/server.ts ─────── createPaidMcpHandler: 3 paidTools, x402 gating
      │
      ├── src/chainalysis.ts ──── sanctions oracle read (viem, Ethereum mainnet)
      └── src/companiesHouse.ts ─ UK Companies House lookup

• `src/server.ts` — defines the three paidTools with their prices and Zod schemas, wired to the Coinbase facilitator for x402 settlement.
• `src/chainalysis.ts` / `src/companiesHouse.ts` — the check logic, reused unchanged from the HTTP API so results stay consistent across rails.
• `index.ts` — a Hono app exposing the handler at /mcp; deployed as a Vercel function, and the same app is served locally by src/local.ts.
• `test/client.ts` — a low-level test client that performs the full x402 pay-and-retry loop by hand (see Design notes).

Sanctions data

Screening reads the Chainalysis on-chain sanctions oracle — a free, public smart contract on Ethereum mainnet (0x40C57923924B5c5c5455c48D93317139ADDaC8fb), queried with a read-only isSanctioned() call via viem. No Chainalysis API key or commercial relationship is required; the oracle is a public good reflecting US/EU/UN sanctions lists. The per-call fee covers infrastructure, not the data.

Running locally

Requires Node 22+.

npm install
cp .env.example .env   # fill in the values below
npm run dev            # serves http://localhost:3000/mcp

Environment variables:

To exercise the full paid loop against the running server:

# in .env, also set PAYER_PRIVATE_KEY to a wallet funded with testnet USDC + ETH
npm run test:client

Design notes

A few decisions worth explaining, since they reflect real constraints rather than preference:

• Why Base and not Tempo. The HTTP API settles on Tempo, so unifying on one chain would have been cleaner. But the x402-mcp package hardcodes its network type to "base" | "base-sepolia" — Tempo is not a permitted value. Rather than fork the package or write a custom facilitator, this server settles on Base, and OnchainDiligence accepts two rails. The constraint is documented, not papered over.

• The test client is hand-rolled. x402-mcp ships a withPayment helper, but it imports an MCP client API (experimental_MCPClient) that the ai SDK removed in v5. Rather than pin an old ai version, test/client.ts performs the x402 loop directly on the MCP SDK plus x402/client — calling unpaid to get requirements, building a payment header, and retrying with payment in _meta. The server itself doesn't depend on ai, so this is a test-only concern.

• Check logic is shared, not reimplemented. chainalysis.ts and companiesHouse.ts are copied unchanged from the HTTP API so that a result is the same regardless of which rail an agent uses. Consistency across surfaces matters more than DRY across repos here.

Not a compliance program

OnchainDiligence returns factual checks and signed attestations. It is not legal or compliance advice and is not a substitute for a full compliance program. The sanctions oracle returns a match flag, not rich case detail. Results are never cached.

Security

Found a vulnerability? Please report it to [email protected]. Responsible disclosure is appreciated. See onchaindiligence.com/.well-known/security.txt.

License

MIT — see LICENSE.