cryptomonnaie — pay-per-call API over x402

An Express server that sells paid API endpoints over the x402 protocol (USDC payments on Base), built to be consumed by AI agents.

A client (human or agent) calls a paid endpoint → the server replies 402 Payment Required with the payment requirements → the client signs a USDC payment and replays the request with the PAYMENT header → a facilitator verifies and settles the payment on-chain → the server serves the response. No blockchain key management server-side: it only holds the receiving address.

Available endpoints

All /api/* routes are paid (x402 payment required), except /health, /stats, and /.well-known/x402.json, which are free. Every response is clean JSON — never a raw 500, always {error: "..."} with the right HTTP status code on any problem (validation, upstream source down, etc.).

Replace $URL with the server's URL (http://localhost:4021 locally, the Render URL in production) in the examples below.

Crypto prices & gas (dedicated routes, optimized for agent search)

Endpoint	Price	Example
GET /api/price/eth-usd	$0.005	curl "$URL/api/price/eth-usd"
GET /api/price/btc-usd	$0.005	curl "$URL/api/price/btc-usd"
GET /api/price/sol-usd	$0.005	curl "$URL/api/price/sol-usd"
GET /api/price/usdc-supply	$0.005	curl "$URL/api/price/usdc-supply"
GET /api/gas/base	$0.005	curl "$URL/api/gas/base"
GET /api/gas/ethereum	$0.005	curl "$URL/api/gas/ethereum"

These are thin, single-purpose wrappers around the same sources as /api/defi/price and /api/chain/gas below — kept as separate routes (with narrow, intent-matching descriptions) so an agent searching for e.g. "ETH price USD" or "gas price Base" finds and calls them directly, instead of having to first discover the generic parameterized endpoint.

Crypto / DeFi data (source DefiLlama, free and open)

⚠️ License note: DefiLlama's terms of service restrict their free API to personal, non-commercial use and prohibit commercial exploitation of the data without prior written agreement (defillama.com/terms, clauses 7 and 8.10). These endpoints (plus the 6 /api/price/* and /api/gas/* ones above, and the 4 /api/defi/yields/* sub-routes below, all of which reuse the same DefiLlama sources) are built on it anyway, on the explicit and informed decision of this service's operator (compliance risk accepted) — to be revisited if DefiLlama raises the issue, or by moving to their paid Pro API (pro-api.llama.fi) if needed.

Endpoint	Price	Example
GET /api/defi/price	$0.005	curl "$URL/api/defi/price?coins=ethereum,bitcoin"
GET /api/defi/tvl	$0.005	curl "$URL/api/defi/tvl?protocol=aave"
GET /api/defi/tvl-chain	$0.005	curl "$URL/api/defi/tvl-chain?chain=base"
GET /api/defi/protocols	$0.005	curl "$URL/api/defi/protocols?limit=20"
GET /api/defi/yields	$0.005	curl "$URL/api/defi/yields?chain=base&min_tvl=1000000"
GET /api/defi/yields/top	$0.005	curl "$URL/api/defi/yields/top?limit=10&min_tvl=10000000"
GET /api/defi/yields/by-token	$0.005	curl "$URL/api/defi/yields/by-token?symbol=USDC&limit=10"
GET /api/defi/yields/by-chain	$0.005	curl "$URL/api/defi/yields/by-chain?chain=base&limit=10"
GET /api/defi/yields/pool	$0.005	curl "$URL/api/defi/yields/pool?pool=<pool id>"
GET /api/defi/stablecoins	$0.005	curl "$URL/api/defi/stablecoins?limit=20"

/api/defi/yields/top, /by-token, /by-chain, and /pool are dedicated, intent-matching routes alongside the generic /api/defi/yields — for an agent searching "best yield for USDC" or "best yields on Base" rather than discovering the generic parameterized endpoint first (same rationale as the dedicated /api/price/* and /api/gas/* routes above). /pool returns one pool's detail plus its last 30 recorded APY/TVL data points, via DefiLlama's yields.llama.fi/chart/{pool} (verified live against the current DefiLlama docs before use — see endpoints/defi-yields-pool.js for a note on a doc/reality mismatch found in the process: the docs list /chart/{pool}'s base URL as api.llama.fi, but only yields.llama.fi actually serves it; api.llama.fi/chart/{pool} 404s).

On-chain data (public RPC reads via viem, no third-party API)

Endpoint	Price	Example
GET /api/chain/gas	$0.005	curl "$URL/api/chain/gas?chain=base" (or chain=ethereum)
GET /api/chain/block	$0.005	curl "$URL/api/chain/block?chain=base"

Web reading & extraction (fetch, readability, and — for extract — Claude Haiku 4.5)

Endpoint	Price	Example
POST /api/web/read	$0.005	curl -X POST "$URL/api/web/read" -H "Content-Type: application/json" -d '{"url":"https://en.wikipedia.org/wiki/HTTP_402"}'
POST /api/web/extract	$0.02	curl -X POST "$URL/api/web/extract" -H "Content-Type: application/json" -d '{"url":"...","schema":{"type":"object","properties":{"title":{"type":"string"}}}}'

POST /api/web/read downloads a page and returns its main content as clean Markdown (readability extraction — boilerplate/nav/ads stripped), so an agent never has to parse raw HTML. POST /api/web/extract does the same fetch, then extracts structured JSON from the page according to a caller-supplied JSON Schema, via Claude Haiku 4.5 — one call instead of read-then-extract. Both are guarded against SSRF (see lib/web.js): the target URL must be public http(s), private/loopback/link-local/reserved IP ranges are refused (checked both on the initial host and on every redirect hop), the download is capped at 2 MB within a 10 s budget, and the site's robots.txt is honored (fails open — i.e. allows the fetch — only when robots.txt itself is unreachable, the same convention real crawlers use).

Open public data

Endpoint	Price	Source / license	Example
GET /api/fx/rates	$0.005	Frankfurter (MIT, open ECB data)	curl "$URL/api/fx/rates?base=EUR"
GET /api/github/repo	$0.005	GitHub REST API	curl "$URL/api/github/repo?full_name=expressjs/express"
GET /api/npm/package	$0.005	registry.npmjs.org + api.npmjs.org	curl "$URL/api/npm/package?name=express"
GET /api/hn/top	$0.005	Hacker News Firebase API (MIT)	curl "$URL/api/hn/top?limit=20"
GET /api/wiki/summary	$0.005	Wikimedia REST API (CC BY-SA 4.0, attribution included in the response)	curl "$URL/api/wiki/summary?title=Bitcoin&lang=en"
GET /api/dns/lookup	$0.005	Direct DNS resolution (Node's dns module)	curl "$URL/api/dns/lookup?domain=example.com"
GET /api/rdap/domain	$0.005	rdap.org (open protocol, WHOIS's successor)	curl "$URL/api/rdap/domain?domain=example.com"

AI tasks (Claude Haiku 4.5, ANTHROPIC_API_KEY required)

Endpoint	Price	Example
POST /api/ai/summarize	$0.01	curl -X POST "$URL/api/ai/summarize" -H "Content-Type: application/json" -d '{"text":"...","max_sentences":3}'
POST /api/ai/classify	$0.01	curl -X POST "$URL/api/ai/classify" -H "Content-Type: application/json" -d '{"text":"...","labels":["positive","negative","neutral"]}'
POST /api/ai/translate	$0.01	curl -X POST "$URL/api/ai/translate" -H "Content-Type: application/json" -d '{"text":"...","target_lang":"French"}'
POST /api/ai/extract	$0.02	curl -X POST "$URL/api/ai/extract" -H "Content-Type: application/json" -d '{"text":"...","schema":{"type":"object","properties":{"total":{"type":"number"}}}}'

Premium reseller (Tavily, Serper — real third-party providers, real margin)

Endpoint	Price	Example
POST /api/search/web	$0.01	curl -X POST "$URL/api/search/web" -H "Content-Type: application/json" -d '{"query":"latest developments in the x402 protocol","num_results":5}'
POST /api/search/serp	$0.005	curl -X POST "$URL/api/search/serp" -H "Content-Type: application/json" -d '{"query":"best crypto payment protocols 2026","country":"us"}'

Unlike the rest of this server (free/public sources, or a flat-rate AI call), this family resells a paid upstream provider's API per call — so margin, compliance, and upstream outages are real, ongoing concerns, tracked deliberately rather than assumed away.

A third endpoint, POST /api/web/scrape (Tavily Extract), was built, shipped, then retired on 2026-09-03. It was removed after a real 6-page comparative test (3 JavaScript-rendered pages, a heavy documentation page, a product page, and an article behind a cookie-consent banner — all confirmed robots.txt-compliant before testing) against this server's own free /api/web/read: the in-house extractor matched or beat Tavily Extract on 5 of the 6 pages, usually because Tavily returned a full page dump (navigation and boilerplate mixed in) where Readability went straight to the actual content. Tavily's only reproducible advantage was bypassing a bot-detection block that refused this server's own honestly-identified crawler outright — real, but too narrow to justify a dedicated $0.02 endpoint. Full test data: docs/RAPPORT-P1-PREMIUM.md.