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JSON Schema Guard for Agent Output
x402
JSON Schema Guard for Agent Output is a paid API for AI agents from api.fadeandco.workers.dev, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-29).
Validates a JSON value against a JSON Schema (draft 2020-12 subset) and returns a valid/invalid result, error details with paths, and a sanitized copy with disallowed fields removed.
Price / call$0.001
Success—
StatusUnknown
How this service works
Checks an agent's JSON output against a JSON Schema (draft 2020-12 keywords: type, properties, required, additionalProperties, items, enum, const, length, pattern, minimum/maximum, item counts). Returns valid yes/no, each error with its path and the value with disallowed fields removed. $ref, allOf/anyOf/oneOf, if/then and format return an error instead of passing silently.
Output
Returns a JSON object with: a 'valid' boolean, an 'errors' array where each entry includes the path and nature of the violation, a 'sanitized' copy of the input with disallowed fields removed, a 'removedFields' list of paths that were stripped, a 'checkedAt' ISO timestamp, and a note that unsupported keywords are rejected rather than silently ignored.
Example use cases
Validate LLM output before tool call
“Before I pass this agent-generated JSON to the payment API, validate it against this schema and tell me if anything's missing or has the wrong type — and strip out any extra fields that aren't allowed.”
Enforce required fields in structured form
“I have a JSON response from my AI assistant and a schema that requires 'name', 'age', and 'email' with specific types. Can you check whether the JSON is valid, show me exactly which fields fail and why, and return a sanitized version?”
Catch unsupported schema keywords in agent pipeline
“My agent is producing JSON and I want to make sure the schema I'm using doesn't accidentally rely on unsupported keywords like $ref or anyOf — can you run this value and schema through the guard and flag any issues?”
Technical details
Endpoint
POSThttps://api.fadeandco.workers.dev/api/agent-intel/agent-json-schema-guard?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need to validate AI agent or LLM-generated JSON against a schema before passing it downstream, especially when you also need a sanitized output with disallowed fields stripped. Prefer this over client-side validation when you want a deterministic, server-side check with explicit error paths and automatic field removal. It is particularly well-suited for agentic pipelines where output structure must be enforced and unsupported schema keywords should surface as explicit failures rather than silent passes.
Side effects
- Schema uses unsupported keywords ($ref, allOf, anyOf, oneOf, if/then, format) — returns an error rather than passing silently
- Input 'schema' field is not a valid object — will fail to parse
- Input 'value' is missing — validation cannot proceed
- Malformed JSON in request body — returns parse error
- Schema constraints conflict in ways the subset validator cannot handle
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| value | — | The JSON value to check (any JSON) |
| schema | object | The JSON Schema |
Output
Schema · Response
{
"type": "json",
"example": {
"note": "Subset of JSON Schema 2020-12. Unsupported keywords are rejected, not ignored.",
"valid": true,
"errors": [],
"source": "https://json-schema.org/draft/2020-12",
"checkedAt": "2026-10-23T09:35:20.029Z",
"sanitized": {
"age": 36,
"name": "Ada"
},
"removedFields": [
"/extra"
]
}
}Tags
x402
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