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FairSeal Payload Hash Anchoring (Base Mainnet)
x402
FairSeal Payload Hash Anchoring (Base Mainnet) is a paid API for AI agents from x402.fairseal.io, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-21).
Anchors a SHA-256 payload hash into a Merkle batch on Base mainnet, returning an anchor ID and a polling URL for the resulting on-chain proof.
Price / call$0.02
Success—
StatusUnknown
How this service works
Anchor a SHA-256 payload hash (64 lowercase hex chars) into a Merkle batch on Base mainnet. Payment: $0.001 USDC per submission (batch-settled). Returns anchor_id (202); poll status_url for Merkle proof + on-chain tx hash.
Output
Returns HTTP 202 with an anchor_id and a status_url. Polling the status_url later yields the completed Merkle proof (the hash's inclusion proof within the batch) and the on-chain transaction hash on Base mainnet confirming the batch settlement.
Example use cases
Document provenance timestamping
“I have a SHA-256 hash of a legal contract: b7e3c2a1f09d8456780123456789abcdef0123456789abcdef0123456789abcd. Anchor it to Base mainnet in batch mode so I have on-chain proof of when it existed.”
AI output integrity verification
“We just generated an AI model report and its hash is 9f2d1c4e5a7b8903456789abcdef012345678901abcdef234567890123456789 — anchor it on Base mainnet with batch tier and tag it with metadata noting it's an AI audit record.”
Software release notarization
“Before shipping this release, anchor the SHA-256 digest of our build artifact — d4c3b2a1e0f9876543210fedcba9876543210fedcba9876543210fedcba987654 — to Base mainnet so we have immutable proof of what code shipped and when.”
Technical details
Endpoint
POSThttps://x402.fairseal.io/v2/anchor?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need cheap ($0.001 USDC), blockchain-anchored proof of existence for a SHA-256 hash on Base mainnet with Merkle batch efficiency. Prefer batch tier for cost-sensitive high-volume anchoring; use realtime tier only when you need an immediate on-chain commitment. This is ideal for document notarization, AI output auditing, software release provenance, and compliance evidence where you need a verifiable, tamper-proof timestamp without storing the raw content on-chain.
Side effects
- Invalid payload_hash format (not 64 lowercase hex chars) returns 400 validation error
- realtime tier requested without a valid pro API key returns 403 forbidden
- metadata exceeds 1KB limit returns 400 payload too large
- Payment not fulfilled via x402 protocol returns 402 Payment Required
- Polling status_url before batch settles returns pending status (batch settles ~60s)
- Network or Base mainnet congestion may delay on-chain confirmation beyond expected ~60s window
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| tier | string | batch (default, ~60s). realtime requires a pro API key and is not available via x402. |
| metadata | object | Optional metadata (max 1KB). Stored with receipt. |
| payload_hash | string | SHA-256 hex of content to anchor (64 lowercase hex chars) |
Tags
x402
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