LLM Structured Output Validator

Presets:
JSON Schema (draft-07)
JSON Output to Validate

Supported Validations

typerequiredenumconstpatternminLength / maxLengthminimum / maximumexclusiveMinimum / exclusiveMaximumminItems / maxItemsminProperties / maxPropertiesadditionalPropertiesitems (array)nested objectsinteger

What This Tool Does

LLM Structured Output Validator is built for deterministic developer and agent workflows.

Validate LLM structured outputs against JSON Schema draft-07. Presets for OpenAI, Anthropic, and MCP formats with detailed error reporting.

Use How to Use for execution steps and FAQ for constraints, policies, and edge cases.

Last updated:

This tool is provided as-is for convenience. Output should be verified before use in any production or critical context.

Agent Invocation

Best Path For Builders

Dedicated API endpoint

Deterministic outputs, machine-safe contracts, and production-ready examples.

Dedicated API

https://aidevhub.io/api/schema-validator/

OpenAPI: https://aidevhub.io/api/openapi.yaml

POST /api/schema-validator/ Validate a tool schema

Unified Runtime API

https://aidevhub.io/api/tools/run/?toolId=structured-output-validator&a=...

GET and POST are supported at /api/tools/run/ with identical validation and limits.

Limit: req / s, input max 256 KB.

REST API

Base URL

https://aidevhub.io/api/schema-validator/

50 requests/day per IP. No authentication required. CORS enabled. OpenAPI spec

Endpoints

POST /api/schema-validator/ Validate a tool schema

Example

curl -X POST https://aidevhub.io/api/schema-validator/ -H "Content-Type: application/json" -d '{"schema": "{\"type\": \"object\"}", "target": "openai"}'

Example Response

{
  "valid": true,
  "errors": [],
  "warnings": [],
  "fixed_schema": null
}

How to Use LLM Structured Output Validator

  1. 1

    Define JSON Schema

    Paste your JSON Schema or select from templates (object with properties, array of records, etc.). The tool validates the schema itself.

  2. 2

    Paste LLM output

    Copy the structured response from your LLM (Claude, GPT, etc.) into the validation panel. Format can be JSON, YAML, or markdown code block.

  3. 3

    Validate against schema

    Click 'Validate' to check if the output matches the schema. Shows specific field violations (type mismatch, missing required fields, enum mismatches).

  4. 4

    Debug errors

    The tool highlights which fields failed validation and why. Suggests corrections for common issues like wrong data types or invalid enums.

  5. 5

    Fix and retry

    Edit the JSON inline and re-validate. Once passing, export as TypeScript types or use in your application code.

Frequently Asked Questions

What is structured output from an LLM?
Structured output is JSON that follows a predefined schema, used in function calling responses, tool results, and data extraction. Both OpenAI and Anthropic support structured output modes.
What JSON Schema versions are supported?
The validator supports JSON Schema draft-07 features including type validation, required fields, enums, patterns, min/max values, minLength/maxLength, and nested object/array validation.
How do I fix 'missing required field' errors?
The error shows which field is missing and its expected type. Either adjust your prompt to ensure the LLM includes the field, or update your schema to make the field optional by removing it from the required array.
Can I generate sample valid output from a schema?
Yes, click 'Generate Sample' to create a valid JSON object filled with placeholder values matching your schema. This is useful for testing and as a reference for expected output structure.
Does this replace JSON Formatter?
No. JSON Formatter validates JSON syntax (is this valid JSON?). This tool validates JSON structure against a schema (does this JSON match the expected shape?). They complement each other.