Listing kit
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Name
Kairostamp
Tagline51/60 chars
Pay-per-call web evidence API for autonomous agents
Short description120/160 chars
Kairostamp: 10 pay-per-call web evidence endpoints for agents. x402 exact USDC on Base mainnet, no accounts or API keys.
Directory blurb276/280 chars
Kairostamp is a machine-to-machine web evidence API. An agent calls an endpoint, gets a 402 with x402 payment terms, pays exact USDC on Base mainnet, and receives the result plus a time-stamped, hash-chained receipt it can verify later. 10 endpoints at $0.005–$0.020 per call…
Medium description317/500 chars
Kairostamp is a machine-to-machine web evidence API. An agent calls an endpoint, gets a 402 with x402 payment terms, pays exact USDC on Base mainnet, and receives the result plus a time-stamped, hash-chained receipt it can verify later. 10 endpoints at $0.005–$0.020 per call. No signup, no API keys, no subscription.
Long description
Paid machine-to-machine web evidence API. Fetches one public http/https URL server-side and returns a time-stamped, tamper-evident receipt; the change-check endpoint also compares it against a caller-supplied baseline. Payment is x402 version 2, scheme "exact", USDC on Base mainnet. A compliant client negotiates payment automatically from the 402 response — there is no account, no API key and no subscription; the agent's wallet is the account. Endpoints (10): snapshot, change-check, digest, headers, verify, robots-check, redirect-audit, text-extract, link-map, sitemap. Pricing: $0.005–$0.020 per call. Every paid call writes to an append-only, hash-chained evidence log and returns a receipt id that can be re-verified later. Order of operations is verify payment, fetch, then settle, so a failed fetch is not charged. Fetching runs in an isolated, IP-pinned service: http/https only, private ranges blocked, DNS pinned against rebinding, 3 redirects maximum, 10 second deadline and a 1 MiB body cap. Machine-readable descriptors: OpenAPI 3.1 at https://kairostamp.com/openapi.json, an agent card at https://kairostamp.com/.well-known/agent-card.json, an x402 resource index at https://kairostamp.com/.well-known/x402, and a plain-text index at https://kairostamp.com/llms.txt.
Pricing
$0.005–$0.020 per call, x402 exact USDC on Base mainnet. No subscription.
Authentication
None. Payment replaces authentication (x402 v2, scheme exact).
Primary category
Developer tools / Agent tools / Web data
Contact
support@kairostamp.com
Categories and keywords
Categories
Agent tools · Web data · Evidence & provenance · x402 / pay-per-call APIs
Keywords
x402, pay per call api, agent tools, web evidence, url snapshot, tamper evident receipt, usdc, base, no api key, snapshot, change-check, digest, headers, verify, robots-check, redirect-audit, text-extract, link-map, sitemap
Links
All links
- Homepage:https://kairostamp.com
- Documentation:https://kairostamp.com/docs
- OpenAPI 3.1:https://kairostamp.com/openapi.jsonmachine
- Agent card:https://kairostamp.com/.well-known/agent-card.jsonmachine
- x402 resource index:https://kairostamp.com/.well-known/x402machine
- llms.txt:https://kairostamp.com/llms.txtmachine
- Discovery document:https://kairostamp.com/api/public/discoverymachine
- Listing kit (JSON):https://kairostamp.com/listing-kit.jsonmachine
- Terms:https://kairostamp.com/terms
- Privacy:https://kairostamp.com/privacy
Endpoint table
| Endpoint | Method | Price |
|---|---|---|
https://kairostamp.com/api/v1/snapshot Kairostamp evidence snapshot: server-side fetch of one public http/https URL, returning a time-stamped receipt with the response status, content type, byte length, SHA-256 of the body, redirect chain, a text preview, and a tamper-evident hash-chain entry. | POST | see 402 |
https://kairostamp.com/api/v1/change-check Kairostamp change check: server-side fetch of one public http/https URL, compared against a baseline the caller already holds. | POST | see 402 |
https://kairostamp.com/api/v1/digest URL digest receipt: server-side fetch of one public http/https URL, returning a time-stamped receipt with the HTTP status, final URL, content type, byte length, SHA-256 of the response body, redirect chain, receipt id and tamper-evident hash-chain entry. | GET | $0.01 |
https://kairostamp.com/api/v1/headers URL HTTP metadata receipt: server-side fetch of one public http/https URL, returning only transport metadata — HTTP status, final URL, redirect chain, content type and byte length — plus a receipt id. | GET | $0.005 |
https://kairostamp.com/api/v1/verify Receipt verification: read-only hash-chain verification of one existing Kairostamp receipt id. | GET | $0.005 |
https://kairostamp.com/api/v1/robots-check robots.txt check: fetches the origin's /robots.txt server-side and reports whether a given URL path is allowed or blocked for a user agent, with the matched rule, the robots URL, the HTTP status, a timestamp and a tamper-evident receipt. | GET | $0.005 |
https://kairostamp.com/api/v1/redirect-audit Redirect audit: follows one public http/https URL server-side and returns the ordered redirect chain, hop count, final URL, final HTTP status, whether the destination changed origin and whether HTTPS was downgraded to HTTP, with a timestamp and a tamper-evident receipt. | GET | $0.01 |
https://kairostamp.com/api/v1/text-extract Readable text extraction: fetches one public HTML page server-side and returns clean plain text with the page title, final URL, HTTP status, content type, SHA-256 of the response body, a timestamp and a tamper-evident receipt. | GET | $0.02 |
https://kairostamp.com/api/v1/link-map Link map: fetches one public HTML page server-side and returns up to 100 normalized, deduplicated http/https links with internal/external classification and counts, the final URL, a timestamp and a tamper-evident receipt. | GET | $0.015 |
https://kairostamp.com/api/v1/sitemap Sitemap lookup: locates a site's sitemap from robots.txt or same-origin /sitemap.xml, fetches it server-side and returns up to 100 normalized http/https URLs with the sitemap URL, document kind, count, truncation flag, a timestamp and a tamper-evident receipt. | GET | $0.01 |
Snippets
See the payment terms (free, spends nothing)
curl -i "https://kairostamp.com/api/v1/digest?url=https://example.com/"Fetch the machine-readable descriptors
curl -s https://kairostamp.com/.well-known/agent-card.json
curl -s https://kairostamp.com/openapi.json
curl -s https://kairostamp.com/llms.txtMarkdown listing line (awesome-lists, README tables)
- [Kairostamp](https://kairostamp.com) — Kairostamp: 10 pay-per-call web evidence endpoints for agents. x402 exact USDC on Base mainnet, no accounts or API keys.Where this goes
- x402 Bazaar (Coinbase CDP discovery index)automatic
Consumes 402 challenge + one settled mainnet payment per route. No form exists. A route is indexed after it validates and takes one settled mainnet payment. Verified with scripts/index-pass.mjs.
- x402 clients probing /.well-known/x402automatic
Consumes /.well-known/x402. Served on every request; needs no submission at all.
- Agent frameworks reading agent cardsautomatic
Consumes /.well-known/agent-card.json. Advertises tools, input schemas, pricing and authentication: none.
- LLM crawlers and RAG pipelinesautomatic
Consumes /llms.txt, /openapi.json, sitemap.xml. robots.txt allows all discovery paths; the sitemap lists them.
- OpenAPI-consuming tool buildersautomatic
Consumes /openapi.json. 402 documented per operation so a generated client knows to pay and retry.
- GitHub awesome-lists and README tablesmanual
Consumes markdown_listing snippet. Needs a pull request from a GitHub account. Copy is pre-written above.
- API and agent-tool directories with signup formsself-serve
Consumes fields + links. Each form field here is already sized to the usual limits. Paste, no writing required.