Preflight402 README
The full upstream README, mirrored here for reference. Install config, tool schemas, adoption signals, and an original overview live on the Preflight402 listing page.
preflight402
One free call before your agent pays. Health, authenticity, and Sybil-filtered reputation — one verdict.
A free trust/health preflight for the agent payment economy (x402). It probes
an endpoint before your agent pays and returns one trust-preview.v1 verdict:
liveness, TLS, the 402 handshake (x402 v1/v2 + MPP detection), price sanity,
continuous uptime history, ERC-8004 identity binding, and Sybil-filtered
on-chain reputation — rolled into a proceed / caution / avoid recommendation
with plain-language reasons. No wallet, no key, no charge.
Why filtered reputation matters: one live agent shows a 99.8/100 average from 996 reviewers — until Sybil filtering collapses those reviewers into 12 independent funding clusters at 89.7. Raw reputation is trivially farmed; this is what the verdict actually scores. (Separately, only ~4% of x402 payees bind to any ERC-8004 identity at all — so most verdicts run on health, price, and handshake, and say so honestly.)
Why "listed" means little: across 7.76M probes over 15 days of a 51,331-endpoint catalog, two squatting hosts account for 58% of every listed x402 endpoint — one serving a uniform 404 behind a "This app isn't live yet" placeholder, the other a uniform Cloudflare TLS failure. Strip them out and 87% of real endpoints work; measured per provider, about one host in seven (13.9%) serves no valid 402. Read the findings: What 7.8M probes say about the x402 economy — including why a GET-only crawl (ours included, before we fixed it) overstates x402 invalidity ~2×. Full method and caveats: docs/checkpoint-m3.md.
30-second quickstart
Point any agent at the hosted MCP endpoint — no wallet, no key, no install:
Or check an endpoint over plain HTTP:
Guard every payment automatically
preflight402-guard turns the service into a payment gate for the
x402 Python SDK — safety becomes
default-on instead of something an agent has to remember to call:
It also cross-checks that the payee your client selected matches the endpoint
that was preflighted (the 402's resource URL is attacker-controlled), enforces
an optional max_price_usd ceiling against the actual selected terms, and
fails open by default so your commerce never depends on our uptime. There's
a CLI too: preflight402-guard check <url>. See guard/README.md.
Status
Live at preflight402.ironshell.io and in
the official MCP registry as
io.ironshell/preflight402. The free preflight engine (health + 402 parse +
verdict), continuous probing with uptime history, ERC-8004 binding, and the
Sybil filter are all shipped and serving live. The whole service is free —
there is no paywall.
Use it
As an MCP tool (no wallet, no key)
The preflight tool takes a url and returns a trust-preview.v1 verdict.
Easiest — point any MCP client at the hosted instance, no install:
Or run it yourself over stdio. Claude Code — one line (PyPI publish pending;
until then point --directory at a clone):
Claude Desktop — add to claude_desktop_config.json:
Either way, run it as a hosted HTTP server with
preflight402-mcp --transport streamable-http (serves the same tool at
http://<host>:8000/mcp).
As a REST call
The hosted instance also serves REST:
Or run it yourself (serves REST + MCP on one port):
Development
Requires uv.