JSON Schema generatorGenerators

JSON Schema generator. From a sample to a schema.

Paste one JSON sample. Get a draft 2020-12 schema with types, required keys and string formats, plus the input_schema block for the Anthropic API and the parameters block for an OpenAI function. Arrays merge every item's shape. Nothing leaves your browser.

Cost to you

Free

Runs in your browser. No signup, no API call, no limit per hour.

browser
runs in: none
API calls: none
account

Use it now

Use the JSON Schema generator here

It runs in your browser. Nothing you type is sent anywhere, there is no signup and no limit.

JSON Schema

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "create_order",
  "type": "object",
  "properties": {
    "order_id": {
      "type": "string",
      "format": "uuid"
    },
    "customer": {
      "type": "object",
      "properties": {
        "name": {
          "type": "string"
        },
        "email": {
          "type": "string",
          "format": "email"
        }
      },
      "required": [
        "name",
        "email"
      ],
      "additionalProperties": false
    },
    "placed_at": {
      "type": "string",
      "format": "date-time"
    },
    "total": {
      "type": "number"
    },
    "paid": {
      "type": "boolean"
    },
    "items": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "sku": {
            "type": "string"
          },
          "quantity": {
            "type": "integer"
          },
          "note": {
            "type": [
              "string",
              "null"
            ]
          }
        },
        "required": [
          "sku",
          "quantity",
          "note"
        ],
        "additionalProperties": false
      }
    }
  },
  "required": [
    "order_id",
    "customer",
    "placed_at",
    "total",
    "paid",
    "items"
  ],
  "additionalProperties": false
}

Runs in your browser, nothing is sent anywhere. One sample shows one shape: add items with the other variants to cover them.

Run it from your agent

Copy one prompt, give it to your agent.

Fill in the placeholder, paste it, and the agent runs the same job with current data on your looot account and shows the cost.

You give it: a json sample: an object, an array or a value.
Billed per call, nothing while your agent is idle.
The agent shows the price before it calls.

Prompt: JSON Schema generator

Use looot to give my agent a typed tool from this sample JSON: [paste it]. 1. Set up https://looot.ai/skill.md. 2. Write a JSON Schema draft 2020-12 for the sample, every key required, additionalProperties false. 3. Wrap it as a tool definition for the API my agent uses. 4. Run one catalog endpoint whose output matches the schema and check the answer validates.

Give this to your agent

Setup command

set up looot - https://looot.ai/skill.md

What comes back

What your agent gets from json schema generator

Field names as the providers return them. The exact set varies by endpoint, and your agent reads it from the catalog.

JSON Schema draft 2020-12
Anthropic tool with input_schema
OpenAI function with parameters
required keys and string formats

Use it for

What people do with json schema generator

Tool calling
Turn a sample request body into the input schema of a tool your model can call.
Structured output
Pin the shape you want back from a model, then validate every answer against it.
Validate API data
Check webhook payloads or API answers against the schema in tests.
Skip the hand typing
Get nested objects, arrays and nullable fields right without writing the schema by hand.

Set up once

Three steps. Your agent does the rest.

Paste one prompt into your agent

Set up looot

Done, looot is connected.

Copy one prompt from /connect into Claude Code, Cursor, or any MCP agent. No SDK, no dashboard click-through first.

Your agent finds the right operation

Hunter$0.0265

Exa$0.0090

Diffbot$0.0032

The agent finds the operation it needs and sees the price first. It calls nothing blind.

You watch what it cost

Hunter$0.0265

Exa$0.0090

Diffbot$0.0032

Total$0.0387

Every call settles for its quoted price and lands in the ledger. You always know what ran and what it cost.

Keep going

Generators
LLM tool schema generator
One tool definition in the Anthropic, OpenAI, Gemini or MCP format, from a name, a description and parameters.
Free, no signupno limit
Formatters
JSON formatter and validator
Pretty prints or minifies JSON, sorts keys and points to the exact line and column of any syntax error.
Free, no signupno limit
Generators
Mock data generator
Up to 1,000 rows of fake test data as JSON, JSON Lines or CSV from a field list.
Free, no signupno limit

FAQ

Questions about json schema generator

Paste a sample. The generator reads each value's type, builds properties for every object, merges the items of each array into one shape and marks keys as required. The schema updates as you type.

Draft 2020-12. The $schema line says so. The tool wrappers leave $schema out, as the model APIs expect.

Every item is read and the shapes are merged. A key missing from some items is not required unless Every field required is on. A value that is null in one item and a string in another becomes a nullable string.

That tool builds a schema from fields you list by hand. This one infers it from real JSON, which is faster when you already have a sample payload.

Turn on Every field required and Strict objects and the OpenAI output gets strict: true. Strict mode needs every key required and additionalProperties false on each object.

date-time, date, email, uri and uuid, by pattern. Turn String formats off if a field only looks like one by chance.

No. Everything runs in your browser. There is no account and no limit.

For agents

tool: JSON Schema generator
category: Generators
input: A JSON sample: an object, an array or a value
output: JSON Schema draft 2020-12, Anthropic tool with input_schema, OpenAI function with parameters, required keys and string formats
price: per call, read live from the catalog on the web page
web tool: runs in the visitor's browser, no API call, free and unlimited
schedule: on demand
setup: https://looot.ai/skill.md
llms.txt: https://looot.ai/llms.txt
updated: 2026-10-14

markdown /free-tools/json-schema-generator.md

Run json schema generator from your own agent.

Start your workspace, top up, and paste the prompt into the agent you already use. It runs the job with live data and shows the cost first.

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