# s2ar Assert

> 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.

## Facts

- Endpoint: GET https://api.s2ar.dev/x402/v1/assert?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/s2ar-assert-6f5dc020
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_j92Ko-cFtg2XfZ3pbfIzr

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 s2ar-assert-6f5dc020
```

Example prompt: Can you assert my agent's JSON output against the schema '{"type":"object","required":["answer","confidence"]}' and also check it's under 500 characters, using the checks '["json_schema","max_length"]'? Here's the text: '{"answer":"Paris","confidence":0.95}'

## When to prefer this

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.

## Known failure modes

- 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

## 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.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "queryParams"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "text": {
       "type": "string",
       "description": "the output to assert (or `json`, an object)"
      },
      "checks": {
       "type": "string",
       "description": "the checks; on GET, a JSON list in one parameter"
      },
      "rubric": {
       "type": "string",
       "description": "a named check list; `schema`, `domains` fill its slots"
      },
      "schema": {
       "type": "string",
       "description": "for json_schema / api-response"
      },
      "source": {
       "type": "string",
       "description": "the source for quotes_in_source"
      }
     },
     "additionalProperties": {
      "type": "string"
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/s2ar-assert-6f5dc020/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.s2ar.dev](https://www.zero.xyz/host/api.s2ar.dev/llms.txt)