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FabTally Web Attestation
x402
FabTally Web Attestation is a paid API for AI agents from fabtally.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).
Fetches a public URL and returns a signed, timestamped attestation asserting whether the page exists, contains a specific substring, or matches a content hash
Price / call$0.01
Success—
StatusUnknown
How this service works
FabTally gives instant, accurate quotes for digital fabrication jobs. Launching soon.
Output
A signed JSON object containing: the normalized URL, the check type performed, the boolean or hash result, a SHA-256 of the response body, the HTTP status code, the final URL after redirects, the full redirect chain, the timestamp of observation, a subset of response headers, and an Ed25519 cryptographic signature from the attestor (attest.fabtally.com/v0) with key ID and public key — plus an error object if the fetch failed, which is itself attested and signed.
Example use cases
Price monitoring with signed proof
“Verify that https://acmesupplier.com/wholesale-pricing contains the text '£12.50 per unit' and give me a signed, timestamped attestation I can show my procurement team as evidence of the price at this moment.”
Confirming a public document is live
“Check whether https://docs.mycompany.com/terms-of-service is publicly reachable right now — I need a signed attestation confirming it returned a 200 OK so I can include it in a compliance report.”
Content integrity hash for audit trail
“Fetch https://regulations.example.gov/rule-42 and return a SHA-256 hash of the page body with a signed timestamp — I want to prove later that the content hasn't changed since today.”
Technical details
Endpoint
POSThttps://fabtally.com/agent/v1/attestWhen to prefer
Use this endpoint when you need a cryptographically verifiable, tamper-evident, point-in-time record that a public URL existed, contained specific text, or had a particular content hash — particularly for compliance, audit trails, competitive intelligence snapshots, or dispute resolution. It is distinct from simple HTTP HEAD checks because it returns an Ed25519-signed attestation with a full redirect chain and body hash, not just a status code. Prefer it over screenshot services when you need machine-readable signed proof rather than visual evidence.
Side effects
- DNS failure for the target URL — error object returned but attestation still signed
- Target URL times out — error returned with signed timestamp
- URL resolves to a private/loopback/link-local IP — refused with blocked address error
- Non-2xx HTTP response from target — error returned, observation still attested
- Response body exceeds size limit — oversized body error
- needle not provided when check=contains — likely validation error
- Payment not included or insufficient — 402 Payment Required before attestation runs
- Target URL redirects to a private IP at any hop — refused
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| urlrequired | string | Absolute http(s) URL to observe. Must resolve to a public IP; private/loopback/link-local ranges are refused at every redirect hop. |
| checkrequired | string | What to assert: "exists", "contains" (needs needle), or "hash". |
| needle | string | Substring to look for when check="contains". 1024 chars max. |
Output
Schema · Response
| Field | Type | Description |
|---|---|---|
| url | string | The URL as requested (normalized). |
| check | string | |
| error | — | Set when the observation could not be completed as a 2xx fetch (DNS failure, timeout, blocked address, non-2xx status, oversized body). The attestation is still returned and still signed — 'the URL did not respond at time T' is itself an observation. |
| needle | — | |
| result | — | Boolean for exists/contains; sha256 hex string for hash; null if unobtainable. |
| sha256 | — | sha256 (hex) of the exact response bytes received. |
| attestor | string | |
| finalUrl | — | URL after following redirects. |
| bodyBytes | — | |
| fetchedAt | string | UTC ISO-8601 timestamp of the observation. |
| redirects | array | Every redirect hop taken, in order. |
| signature | object | ed25519 signature over the canonical JSON of this object with the `signature` field removed and keys serialized in the documented order. Verify with the public key from GET /agent/v1/attest/schema. |
| disclaimer | string | |
| httpStatus | — | Status of the final hop; null if the fetch failed. |
| headersSubset | object |
Tags
x402
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