# Kairostamp Change Check

> Kairostamp Change Check is a paid API for AI agents from kairostamp.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-11).

Fetches a public URL server-side, compares its response body against a prior SHA-256 or Kairostamp receipt, and returns whether the content changed along with a new tamper-evident timestamped evidence receipt.

## Facts

- Endpoint: POST https://kairostamp.com/api/v1/change-check?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/kairostamp-change-check-c51a526d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Y2OiW_HSNgcnfK5XijDQz

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability kairostamp-change-check-c51a526d -d '<json body>'
```

Example prompt: Check whether https://example.com/terms-of-service has changed since I last saw it — use this prior SHA-256 as the baseline: a3f1c2e4b5d6789012345678901234567890123456789012345678901234abcd, and give me a timestamped receipt of the result.

## When to prefer this

Use this endpoint when you need both a change-detection answer and a cryptographic, tamper-evident audit trail in a single call. It is ideal for compliance monitoring, legal evidence gathering, or automated alerting workflows where you need a hash-chain receipt proving the state of a URL at a specific moment. Prefer it over simple diff tools or basic polling when tamper-evident provenance matters, or when you already have a prior Kairostamp receipt ID and want to chain evidence. For first-time snapshots with no prior baseline, use the sibling URL digest receipt endpoint first.

## Known failure modes

- URL is not publicly reachable or returns an error status — check fails with a fetch error
- URL uses a non-http/https scheme — rejected as invalid input
- Neither prior_sha256 nor prior_receipt_id supplied — request rejected
- Both prior_sha256 and prior_receipt_id supplied simultaneously — request rejected with conflict error
- prior_receipt_id refers to an unknown or expired receipt — lookup failure
- URL returns a redirect to a private or non-routable address — blocked for security
- Response body too large to hash within timeout — fetch timeout error

## How this service works

Kairostamp change check: server-side fetch of one public http/https URL, compared against a caller-supplied prior SHA-256 or prior Kairostamp receipt id. Returns whether the response body changed, both digests, and a new time-stamped evidence receipt with its tamper-evident hash-chain entry. One call performs one check; repeat monitoring means calling again.

## Output

Returns a JSON object indicating whether the response body changed (boolean), the current SHA-256 digest of the fetched page, the prior SHA-256 digest used for comparison, a new Kairostamp evidence receipt with a UUID receipt ID, a timestamp, and a tamper-evident hash-chain entry linking this check to the prior receipt or hash.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/kairostamp-change-check-c51a526d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from kairostamp.com](https://www.zero.xyz/host/kairostamp.com/llms.txt)