# AttestPage SHA-256 Timestamping Service

> AttestPage SHA-256 Timestamping Service is a paid API for AI agents from s2h6qt73jtzlgbgnnfacln2poq.srv.us, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-17).

Creates a signed, timestamped cryptographic receipt for a SHA-256 hash, proving a file or record existed unchanged at a specific point in time

## Facts

- Endpoint: POST https://s2h6qt73jtzlgbgnnfacln2poq.srv.us/v1/attest?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/attestpage-sha-256-timestamping-service-3c71a46a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_qfoSSZUPrfuA91tG0Hna3

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 attestpage-sha-256-timestamping-service-3c71a46a -d '<json body>'
```

Example prompt: Attest this SHA-256 hash for me — e4d909c290d0fb1ca068ffaddf22cbd0d3e9a7b4b7e5c3c7f4f3c5b7a1d2e3f4 — and include the note 'Q2 financial report final version' so I have a signed timestamped receipt proving it existed right now.

## When to prefer this

Use this endpoint when you need cryptographic, verifiable proof that a specific file, record, or piece of data existed unchanged at a given point in time — without revealing the content itself (only the hash is submitted). Prefer this over simple database logging when the proof needs to be independently verifiable and tamper-evident. Use /v1/fetch instead when you need to attest what a live web page said at a given time, as that endpoint captures and hashes the page contents itself.

## Known failure modes

- Invalid SHA-256 format (not 64 hex characters) returns a 400 error
- Idempotency key used with a different sha256 than the original returns 409 Conflict
- Idempotency key used outside of x402 payment context returns 400
- Payment not completed or insufficient funds prevents attestation
- Note exceeds 280 character limit returns validation error
- Network timeout or service unavailability returns 5xx error

## How this service works

Signs a timestamped receipt for a file's sha256, proving it existed unchanged then. US$0.002 per call; POST the hash.

## Output

A signed, timestamped cryptographic receipt confirming that the submitted SHA-256 hash was attested at a specific moment in time. The receipt is verifiable: any future version of the file that produces a different hash will not match, proving tampering or alteration. With an idempotency key, retrying the same hash returns the identical original receipt rather than creating a new record.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "note": {
   "type": "string",
   "maxLength": 280,
   "description": "Optional note; only its SHA-256 goes in the receipt."
  },
  "sha256": {
   "type": "string",
   "pattern": "^[0-9a-fA-F]{64}$",
   "description": "SHA-256 (hex) of the thing being attested."
  },
  "idempotency_key": {
   "type": "string",
   "maxLength": 128,
   "description": "Optional, x402 payments only (keys are scoped to the paying address; trial and L402 calls get 400). Retries with the same key and sha256 get the same attestation (the receipt names that call own payment tx); a different sha256 gets 409."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/attestpage-sha-256-timestamping-service-3c71a46a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from s2h6qt73jtzlgbgnnfacln2poq.srv.us](https://www.zero.xyz/host/s2h6qt73jtzlgbgnnfacln2poq.srv.us/llms.txt)