@tensorfeed/x402-base-mcp

Read-only MCP server for verifying x402 USDC settlements on Base mainnet. Drop it into any MCP-compatible agent (Claude Desktop, Claude Code, Cursor, ChatGPT) to independently audit x402 payment receipts on-chain, parse publisher .well-known/x402 manifests, and check AFTA federation status. No private keys, no signing, no broadcasts.

npm install -g @tensorfeed/x402-base-mcp

Relationship to Coinbase Base MCP

Coinbase shipped Base MCP (the official mcp.base.org server, launched May 2026) as the transact-side MCP: it connects an agent to a Base Account and lets the agent propose swaps, transfers, and x402 payments that the user approves in-wallet.

This package, @tensorfeed/x402-base-mcp, is the verify-side MCP. Once an x402 payment has been made (by Base MCP, by a server-side @coinbase/x402 middleware, or by any other x402 client), this server lets the calling agent independently check the on-chain settlement, parse the publisher's /.well-known/x402 manifest, and audit the receipt. Read-only chain visibility, no wallet.

The two are complementary, not competing. Use Base MCP to pay. Use this MCP to verify.

Why a separate verify MCP

x402 is a payment protocol where agents pay merchants in USDC on Base for paid API responses. When an agent receives a payment receipt back, it has two options for confirming that the settlement actually happened the way the receipt claims:

1. Trust the merchant
2. Read the on-chain Transfer event itself

Most existing EVM MCP servers either require a private key (so the agent can also send transactions, which is operationally risky and unnecessary for verification), or are generic multi-chain readers that don't speak x402. This server is the read-only, x402-aware option. Drop it into a Claude Desktop or Claude Code session and any agent can verify x402 payments without operating a wallet.

The TensorFeed-flavor tools (verify_afta_federation, tf_payment_lookup) compose the same primitives against TF's canonical surfaces and demonstrate the pattern. Use them or ignore them; the generic tools work fine on their own.

Installation

Claude Desktop

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "tensorfeed-x402-base": {
      "command": "npx",
      "args": ["-y", "@tensorfeed/x402-base-mcp"]
    }
  }
}

Claude Code

claude mcp add tensorfeed-x402-base -- npx -y @tensorfeed/x402-base-mcp

Optional: bring your own RPC

The server defaults to the public Base RPC (https://mainnet.base.org), which is fine for casual use. For heavier workloads, set an Alchemy or Infura URL via TENSORFEED_RPC_URL. The URL must match the allowlist in src/rpc/allowlist.ts; anything else falls back to the public endpoint and logs a warning to stderr.

export TENSORFEED_RPC_URL="https://base-mainnet.g.alchemy.com/v2/YOUR_KEY"

Affiliate links if you don't already have an account:
- Alchemy: https://www.alchemy.com/
- Infura: https://www.infura.io/

Tools

Generic Base reads

| Tool | Description |
|------|-------------|
| balance | Native ETH balance for an address |
| usdc_balance | USDC (Circle native bridged) balance for an address |
| block_number | Latest Base block number |
| get_tx_receipt | Full tx receipt with status, gas, and logs summary |
| call | Read-only contract call (eth_call, never broadcasts) |
| recent_transfers | USDC Transfer events involving an address over N blocks |

x402-native verification

| Tool | Description |
|------|-------------|
| verify_x402_settlement | Given a tx hash, expected recipient, and expected USDC amount, returns a structured verdict on whether the on-chain Transfer event matches. |
| parse_x402_manifest | Fetches https://{domain}/.well-known/x402.json, returns the structured manifest. |
| usdc_recent_payments_to | USDC transfers TO an address over N blocks; the merchant-side view. |
| probe_x402_endpoint | Probes any https URL and reports whether it returns a canonical x402-paid 402 response with accepts[]. |
| decode_x402_payment_payload | Offline decode of a base64 X-PAYMENT header (Coinbase x402 V2): returns scheme, network, version, EIP-3009 authorization, signature. |

TensorFeed flavor

| Tool | Description |
|------|-------------|
| verify_afta_federation | Calls TensorFeed's AFTA certification endpoint for a domain, returns a scored checklist. |
| tf_payment_lookup | Checks whether a tx hash is a USDC payment to TensorFeed's canonical wallet on Base. |
| x402_publisher_health | Returns current outcome + 24h/7d uptime + recent series for a domain monitored by TensorFeed's hourly x402 status probe. |
| afta_federation_members | Returns the canonical curated list of confirmed AFTA federation members (TF origin + federated members). |

Examples

Verify an x402 settlement (works on TensorFeed's first canonical V2 payment):

verify_x402_settlement({
  tx_hash: "0xe20c57d8aa6df63f75ce7a4e4c0cab492eb7fa672a23cd8fd59967eb6b66bd67",
  expected_recipient: "0x549c82e6bFC54bdaE9A2073744CBC2AF5D1FC6D1",
  expected_amount_usdc: "0.02"
})
// returns { ok: true, verified: true, matches: [...] }

Inspect a publisher's x402 manifest:

parse_x402_manifest({ domain: "tensorfeed.ai" })

Check AFTA certification:

verify_afta_federation({ domain: "tensorfeed.ai" })

Threat model

Read-only chain-visibility MCP. The full picture is in SECURITY.md; the short version:

- No private keys, no signing, no broadcasts. The server cannot move funds.
- Input validators on every tool reject malformed inputs (bad checksums, malformed hashes, URL-shaped domains, private/loopback hostnames).
- Output sanitization strips C0/C1 control characters and zero-width / direction-override marks from every string returned to the calling agent.
- External strings carry an _origin: "external" marker so the calling agent knows the value came from a third party.
- 50 KB response cap on serialized tool output; oversized responses collapse to a structured stub.
- RPC allowlist limits self-hosters to known endpoints; arbitrary URLs are rejected and fall back to public Base RPC.
- No telemetry, no phone-home, no analytics.
- Provenance: npm releases are published via GitHub Actions OIDC with cryptographic provenance attestations. Verify with npm audit signatures.

Report security issues to security@tensorfeed.ai. Please do not file a public issue or CVE for an unfixed vulnerability.

License

MIT

Related

- Coinbase Base MCP - the official transact-side MCP for Base. Pair with this package for a full pay + verify loop: Base MCP signs the x402 payment, this package independently confirms the settlement on-chain.
- @tensorfeed/mcp-server - companion package, the TensorFeed data MCP (news, status, models, benchmarks, premium endpoints). Complementary role: this server verifies x402 payments on-chain; mcp-server wraps the TF data API as MCP tools.
- TensorFeed - AI ecosystem data layer
- TensorFeed developers - free + premium API for AI agents
- Agent Fair-Trade Agreement (AFTA) - open standard for honest agent commerce
- x402 spec - the payment protocol this MCP verifies