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s2ar Assert
x402
s2ar Assert is a paid API for AI agents from api.s2ar.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-11).
Validates agent output against JSON schema, term lists, length constraints, citation rules, and source quotes, returning a signed verification record.
Price / call$0.005
Success—
StatusUnknown
How this service works
Assert an agent's output — JSON schema, terms, lengths, citations, quotes in a source; a signed record. GET ?text=&checks=
Output
A signed record containing per-check pass/fail verdicts for each requested assertion (e.g. json_schema, max_length, terms_present, quotes_in_source), along with a cryptographic signature that any party can verify to confirm the checks were run and what the outcome was.
Example use cases
Verify grounded answer citations
“My agent just wrote an answer about climate change — can you check whether all the quotes in that answer actually appear in the source article I'll paste? Run a quotes_in_source check and give me a signed record I can share.”
Validate API response schema
“I got this JSON back from a third-party API: '{"id":123,"status":"active"}' — can you assert it matches the schema '{"type":"object","required":["id","status","name"]}' so I know if it's well-formed before I process it?”
LLM output term and length gate
“Before I use this LLM-generated product description in production, assert that it contains the terms 'warranty' and 'free shipping' and that it's under 300 characters — run those checks and give me a signed pass/fail record.”
Technical details
Endpoint
GEThttps://api.s2ar.dev/x402/v1/assert?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a tamper-proof, signed record proving that a piece of generated or received content passed specific structural or semantic checks — especially JSON schema conformance, keyword presence, length constraints, or quote grounding in a source. It is ideal for agent pipelines that must produce auditable output QA receipts, or when downstream consumers need to verify that an AI agent's output was validated before use.
Side effects
- Missing required 'text' or 'checks' parameter returns an error
- Malformed JSON in 'checks' list causes a parse error
- Schema provided in 'schema' param is invalid JSON Schema, resulting in a schema-parse error
- Source document not provided when quotes_in_source check is requested
- Unknown rubric name returns a not-found error
- Text too long for the endpoint to process causes a payload error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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