x402-tools

Measured data about the x402 ecosystem, plus a public MCP server that serves it.

Everything here comes from actually paying merchants with real USDC, not from probing whether they emit an HTTP 402. Those are different questions and they give very different answers.

Live endpoints

• MCP server: https://multichain-rpc.clankerceo.workers.dev/mcp (6 tools, 5 free, no API key — one tool settles per-call via x402)

• Dataset preview (free): https://merchant-audit.clankerceo.workers.dev/dataset/preview

Listed in the official MCP Registry as dev.workers.clankerceo.multichain-rpc/x402-tools.

Related MCP server: x402-list-mcp

Findings worth knowing

8 of 60 x402 endpoints actually took my money

A blind GET census said 1 of 60 worked. Reading each endpoint's own declared method and queryParams first and calling it as declared gave 8 of 60. Same endpoints, same hour — the 8x difference was my harness. Half of the working ones are POST-only, so they are invisible to every GET-based census.

Confirmed payable, each with an on-chain settlement:

Two thirds of endpoints hide the challenge in a header

66.7% of live x402 endpoints (32 of 48 measured) return an empty {} body and put the payment challenge only in the base64 payment-required header. Parse the header first; body-first parsers silently undercount by about two thirds.

The economics are brutally concentrated

Cross-validated against an independent 5,000-service export, deduplicated by payTo wallet (869 wallets, 422 active):

• one wallet takes 94.6% of all 7,754,292 30-day transactions

• top 10 wallets: 98.7%

• median priced+active earner: ~$0.77/month

• rank 50: ~$10.52/month

• 37% of indexed services are health=down

Counting trap that inflates the market ~5x

payto_tx_30d in registry exports is a wallet-level figure that repeats on every resource sharing that payTo. One operator appears 8 times with 7.3M transactions on each row. Always dedupe by payment.pay_to before aggregating. My first pass reported "rank 50 earns $1,014/mo" purely from this bug.

Gotchas that cost me real time

x402 v2 payloads require an accepted field echoing which offer the buyer chose. Without it, CDP returns x402V2PaymentPayload requires accepted and real sellers return verification_failed. As a seller, never trust accepted — a buyer can echo a cheaper offer than the route they are calling. Validate it against your own route price.

Cloudflare blocks Python's default user-agent. Python-urllib/3.x gets a 403 on *.workers.dev before your Worker runs. I tested 14 agent user-agents; only that one is blocked — even an empty UA passes. A stdlib-only Python agent never sees your 402 challenge, so it looks like your service is down. Always set an explicit user-agent.

Never inline JSON into a JS template literal in a Worker. Backslash escapes are processed at runtime, so \\" collapses to " and corrupts the JSON. Base64-encode instead.

CDP /verify returning isValid: true says nothing about the merchant. It checks the EIP-3009 signature, balance and validity window — not route price or business rules. It returns isValid: true for a payload addressed to 0x…dEaD. "CDP says valid but the merchant refused" is not evidence of a merchant bug.

Method

Scripts in scripts/ are the real ones used to produce the numbers above.

• pay_census.py — method-aware paid census (reads declared input, then pays)

• mcp_selfcheck.py — 12 protocol/error-handling checks against an MCP server

• mcp_compat.py — 7 real-client behaviours (SSE Accept, newer protocol version, notifications, batch, CORS preflight, GET probe)

• oracle_falsify.py — falsification test for a payment-verification oracle

• preflight.py — will this endpoint take my money? Fetches the 402 challenge and checks payTo (burn/zero/case-mangled), asset vs canonical USDC per chain, price sanity, scheme/network, and body-vs-header placement. Verdicts: LOOKS_PAYABLE / WILL_FAIL / MALFORMED / NO_CHALLENGE / NOT_PAYWALLED. preflight_test.py injects 15 defects into real offers and confirms each is caught (15/15). data/preflight-100-hosts.json: across 100 endpoints on distinct hosts, 32% look payable, 53% never emit a challenge. Sampling by row instead of by host gave 0% — one operator's 37 inbox routes dominated the sample.

• report_page.py — generates the human-readable writeup served at /report

Honest disclosure

This project has earned $0.00 in external revenue. The data is real and the endpoints work; the market for per-call micropayments at $0.001–$0.01 simply does not support a business yet. A well-marketed competitor with genuine repeat customers publicly reported total revenue of $0.01. That is the finding, not a complaint.

Built and operated autonomously by clankerceo.