Validate + coerce to schema API

Validates a (possibly stringified) LLM value against a minimal JSON-Schema and coerces loose types — numeric strings to numbers, yes/no/1 to booleans, integer rounding, min/max clamping, applied defaults — returning the cleaned value, every coercion, and any remaining validation errors. Answers 'how do I force model output to match my schema?', 'how do I clean up loosely-typed JSON from an LLM?'.

Price$0.05per request

MethodPOST

Route/v1/llm/schema-coerce

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

llmjson-schemavalidatecoercestructured-outputfunction-callingtypesagent

API URLhttps://x402.hexl.dev/v1/llm/schema-coerce

Integration docs

Example request

{
  "data": "{\"age\":\"30\",\"active\":\"yes\"}",
  "schema": {
    "type": "object",
    "properties": {
      "age": {
        "type": "integer"
      },
      "active": {
        "type": "boolean"
      },
      "role": {
        "type": "string",
        "default": "user"
      }
    },
    "required": [
      "age"
    ]
  }
}

Example response

{
  "ok": true,
  "valid": true,
  "coerced": {
    "age": 30,
    "active": true,
    "role": "user"
  },
  "errors": [],
  "coercions": [
    "$: parsed-json-string",
    "$.age: string->number",
    "$.active: string->boolean",
    "$.role: applied-default"
  ]
}

Input schema

{
  "type": "object",
  "required": [
    "data",
    "schema"
  ],
  "properties": {
    "data": {
      "description": "The LLM value (object or JSON string) to validate/coerce.",
      "examples": [
        "{\"age\":\"30\",\"active\":\"yes\"}"
      ]
    },
    "schema": {
      "type": "object",
      "description": "Minimal JSON-Schema with type/properties/required/items/enum/default/minimum/maximum."
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}