# Kairostamp — listing kit
Generated 2026-08-23T18:03:30.412Z

## Name
Kairostamp

## Tagline (max 60 chars)
Pay-per-call web evidence API for autonomous agents

## Short description (max 160 chars)
Kairostamp: 10 pay-per-call web evidence endpoints for agents. x402 exact USDC on Base mainnet, no accounts or API keys.

## Directory blurb (max 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 description (max 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
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
- Homepage: https://kairostamp.com
- Documentation: https://kairostamp.com/docs
- OpenAPI 3.1: https://kairostamp.com/openapi.json
- Agent card: https://kairostamp.com/.well-known/agent-card.json
- x402 resource index: https://kairostamp.com/.well-known/x402
- llms.txt: https://kairostamp.com/llms.txt
- Discovery document: https://kairostamp.com/api/public/discovery
- Listing kit (JSON): https://kairostamp.com/listing-kit.json
- Terms: https://kairostamp.com/terms
- Privacy: https://kairostamp.com/privacy

## Endpoints
- POST https://kairostamp.com/api/v1/snapshot — see 402 — 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 https://kairostamp.com/api/v1/change-check — see 402 — Kairostamp change check: server-side fetch of one public http/https URL, compared against a baseline the caller already holds.
- GET https://kairostamp.com/api/v1/digest — $0.01 — 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 https://kairostamp.com/api/v1/headers — $0.005 — 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 https://kairostamp.com/api/v1/verify — $0.005 — Receipt verification: read-only hash-chain verification of one existing Kairostamp receipt id.
- GET https://kairostamp.com/api/v1/robots-check — $0.005 — 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 https://kairostamp.com/api/v1/redirect-audit — $0.01 — 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 https://kairostamp.com/api/v1/text-extract — $0.02 — 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 https://kairostamp.com/api/v1/link-map — $0.015 — 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 https://kairostamp.com/api/v1/sitemap — $0.01 — 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.

## 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.txt

### Markdown 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.