ListSmith

The listing doctor for the x402 Bazaar. A route is discoverable only if its 402 response carries a valid Bazaar discovery extension — and most are broken: 87.8% ship a hollow {"type", "example"} output, descriptions over 500 characters make the CDP facilitator reject payments, and a malformed extension fails facilitator-side validation in silence. The seller just never gets calls. ListSmith grades the damage — and sells the fix. No accounts, no API keys: payment is the authentication.

Live on Base mainnet x402 v2 · exact scheme Grade $0.10 · Fix $0.50 Observation only — never pays the target

The two routes

Route	Price	What you get
`POST /v1/grade`	$0.10	The diagnosis: both x402 SDK validator verdicts, schema-quality score, itemized defects with severities, a 0-100 grade. No repaired content.
`POST /v1/fix`	$0.50	The repair: a complete discovery package — full output schema inferred from one real sample output, a sub-500-char description with a use-when sentence, OpenAPI + well-known snippets, paste-in instructions. Ships only if it passes BOTH SDK validators.

How to call it

curl -X POST https://list-smith-production.up.railway.app/v1/fix \
  -H 'content-type: application/json' \
  -d '{"resource_url":"https://your-service.example.com/v1/route",
       "sample_output":{"your":"real response body"}}'

Unpaid calls return an HTTP 402 x402 challenge. Pay with any x402 v2 client, retry with the payment header, and the report (or the package) comes back. The target endpoint is probed unpaid and is never charged.

Endpoints

Route	Price	Purpose
`POST /v1/grade`	$0.10	Grade one route's discovery metadata (paid, x402)
`POST /v1/fix`	$0.50	Repair one route's discovery metadata (paid, x402)
`GET /quote`	free	Prices, asset, network, pay-to wallet
`GET /.well-known/x402`	free	Machine-readable service manifest
`GET /skill.md`	free	Documentation written for agents
`GET /llms.txt`	free	Compact agent index
`GET /health`	free	Liveness

Source code: github.com/QuincyGB/list-smith (public source — the grading is deterministic and fully inspectable, and the test suite ships with it). Sibling services: RouteVerdict (trust & liveness checks — it finds the hollow listings, ListSmith fixes them) and Token Verdict (risk verdicts for token contracts — whose own broken extension was the first patient).

Honest limits: ListSmith reads what an endpoint publishes unpaid; it never pays the target and never sees the paid payload. The fix's output schema is inferred from ONE sample: fields null in the sample stay untyped, array element schemas are merged, numeric-looking strings stay strings. Metadata alone never lists you — a settled payment through the CDP or PayAI facilitator is what catalogs a route, per facilitator.