# x402lint — Conformance scanner + graded discovery directory for x402 sellers — free cached reports, $0.05 priority fresh scans, paid machine-tier directory export and change feed. Per-call USDC pricing, no signup. (v0.3.0)

> x402lint grades x402 seller origins A-F on 25 conformance checks (protocol surface, agent docs, directory standing) and tells you exactly what to fix. Full cached reports are FREE (GET /v1/report); a paid $0.05 scan forces a fresh run. The graded directory is free to browse; the machine tier (full export + change feed) is paid. Scanning is non-settling (GET/HEAD probes plus one benign empty-JSON POST fallback per candidate route; no real payments are ever made against the target); results cached 24h.

## Base URL
- API: https://api.x402lint.dev
- This document: https://api.x402lint.dev/llms.txt  ·  Extended: https://api.x402lint.dev/llms-full.txt
- Discovery (JSON): https://api.x402lint.dev/discovery
- OpenAPI 3.1: https://api.x402lint.dev/openapi.json
- x402 manifest: https://api.x402lint.dev/.well-known/x402
- Agent card (A2A): https://api.x402lint.dev/.well-known/agent-card.json
- Terms: https://api.x402lint.dev/terms.txt

## Free endpoints (no auth, no payment)

| Method | Path | Description |
|--------|------|-------------|
| GET | /v1/status | Free. Returns whether an origin has been scanned, scan freshness, and the grade summary (grade, score, pass/warn/fail counts) — no per-check findings. Real data from prior scans; full findings are free at GET /v1/report while a fresh result exists; POST /v1/scan runs a fresh scan. (rate limit: 30/min) |
| GET | /v1/checks | Free. The full conformance check catalog: every check's id, title, severity, and category, plus category summaries. Per-origin results (pass/warn/fail, evidence, one-line fixes) are delivered by the paid scan (POST /v1/scan) and cached report (GET /v1/report). (rate limit: 30/min) |
| GET | /v1/report | Free. Returns the full cached scan report (same shape as POST /v1/scan) if a fresh (<24h) result exists; otherwise an uncharged 404 pointing at POST /v1/scan. The zero-cost way to read any origin's latest findings — scan reports land here for 24h. (rate limit: 30/min) |
| GET | /v1/directory | Free. Paginated list of origins x402lint has scanned and graded, with conformance grade, auto-collected UNVERIFIED third-party branding, and ecosystem legitimacy signals. Sort by recency (default) or grade; filter by category, verification, or host substring. A grade measures protocol conformance only and is NOT an endorsement or a safety/legitimacy assessment. hasRecentSettlement is true or null (null = not observed in a bounded most-active-sellers walk, not proof of no settlements). (rate limit: 30/min) |
| GET | /v1/featured | Free. Origins that scored an A on their most recent scan within the last 30 days, recency-ranked. Featured placement is a free consequence of a recent A-grade scan; it expires 30 days after the scan (re-scan to refresh). Conformance only — NOT an endorsement. hasRecentSettlement is true or null (null = not observed in a bounded most-active-sellers walk, not proof of no settlements). (rate limit: 30/min) |
| GET | /v1/project | Free. The public directory record for one origin (grade, branding, legitimacy signals, verification + featured status). 404 uncharged if the origin is unknown or has opted out. hasRecentSettlement is true or null (null = not observed in a bounded most-active-sellers walk, not proof of no settlements). (rate limit: 30/min) |
| POST | /v1/verify/start | Free. Begin domain-control verification of an origin you operate. Returns a one-time token to place at /.well-known/x402lint-challenge on that origin, then call POST /v1/verify/confirm. (rate limit: 10/min) |
| POST | /v1/verify/confirm | Free. x402lint fetches /.well-known/x402lint-challenge over HTTPS and, if it matches the unexpired token from /v1/verify/start, marks the origin owner-verified. (rate limit: 10/min) |
| POST | /v1/listing | Free. For owner-verified origins only (else 403). Opt the origin out of the public directory (listed=false) and/or suppress auto-collected branding (suppressEnrichment=true). (rate limit: 10/min) |

## Paid endpoints (x402 V2, USDC on Base, per-call)

| Method | Path | Price | Description |
|--------|------|-------|-------------|
| POST | /v1/scan | $0.05 | Paid ($0.05). ALWAYS runs a fresh 25-check scan of the origin (non-settling GET/HEAD + benign empty-POST probes), bypassing the 24h cache — use free GET /v1/report to read the cached result. Concurrent requests for the same origin join the in-flight scan rather than double-scanning. Returns grade, score, per-check status + evidence + fix instructions, and a shareable report URL. Unreachable/broken origins are a valid graded result (F). 504 processing responses and errors are never charged. |
| GET | /v1/directory/export | $0.1 | Paid ($0.10). The entire graded directory in one machine-shaped response: every listed origin with grade, score, grade history, legitimacy signals, branding, verification and featured status — the same record shape as /v1/directory plus gradeHistory, firstSeenAt, and scanCount. Capped at 10,000 records (truncated:true if hit). Grades measure protocol conformance only and are NOT endorsements. |
| GET | /v1/changes | $0.03 | Paid ($0.03). Everything that changed in the graded directory since a timestamp: newly listed origins (changeType "new"), grade changes ("grade_changed", with previousGrade/previousScore), and plain re-scans ("rescanned"). Poll this to keep a local copy of the directory fresh without re-buying the full export. An invalid since/limit is an uncharged 400. |

## How to pay (x402)
Each paid call answers a 402 challenge; sign an x402 `exact` USDC authorization for one advertised rail (Base) and retry. Standard @x402 V2 clients send the `PAYMENT-SIGNATURE` header; legacy clients send `X-PAYMENT`. Prices are USD, settled as USDC (6 decimals).

## Links
- Docs: https://api.x402lint.dev/llms.txt
- Full: https://api.x402lint.dev/llms-full.txt
- OpenAPI: https://api.x402lint.dev/openapi.json
- Discovery: https://api.x402lint.dev/discovery
- Agent card: https://api.x402lint.dev/.well-known/agent-card.json
- Website: https://x402lint.dev

## Check catalog
GET /v1/checks returns a high-level summary of the 25 conformance checks grouped into three categories: protocol & payment surface (8), discovery & agent docs (12), and ecosystem standing (5), each with a count and description. The summary is versioned (checksVersion). Full per-check findings, evidence, and one-line fixes come with the paid fresh scan (POST /v1/scan) or free from GET /v1/report while a <24h cached result exists.