# LLM tool schema generator: run it free, or from your agent

One tool definition in the Anthropic, OpenAI, Gemini or MCP format, from a name, a description and parameters.

## Prompt

Use looot to give my agent a tool for [job]. 1. Set up https://looot.ai/skill.md. 2. Search the looot catalog for an endpoint that does the job and read its input parameters. 3. Write a tool definition in the [Anthropic or OpenAI] format whose parameters match the endpoint's required inputs. 4. Return the JSON and one example call.

## What it needs

A tool name, a description and parameters with types

## What comes back

- tool definition JSON per format
- JSON Schema of the parameters
- OpenAI strict mode variant
- download as .json

## Endpoints and providers

None. The tool on the web page runs in the browser and calls no endpoint.

## What it costs

Nothing. The tool on the web page runs in the visitor's browser: no account, no API call and no limit per hour. The prompt above runs the same job from your own looot account with current data, billed per call.

## Give an agent a tool

Write the definition once and paste it into your tools array.

## Switch providers

Move a tool from one API to another without rewriting the JSON by hand.

## Strict mode

Get the OpenAI strict variant with every field required and nulls for optional ones.

## Build an MCP server

Copy the inputSchema your tools/list handler returns.

## What is a function calling schema?

A JSON description of a tool: its name, what it does and a JSON Schema of its parameters. The model reads it and returns arguments that match.

## What is the difference between the Anthropic and OpenAI tool formats?

Anthropic puts the schema in input_schema next to name and description. OpenAI Chat Completions wraps them in a function object with type function. The Responses API keeps them flat.

## What does OpenAI strict mode change?

Every property must be listed as required and additionalProperties must be false. An optional field becomes a union with null, so the model can leave it empty.

## How do I write an MCP tool definition?

Pick MCP. You get name, description and inputSchema, the shape a server returns from tools/list.

## Can a parameter hold an object or an array of numbers?

Not in this generator. Arrays hold strings and there are no nested objects. Edit the JSON after you copy it for those.

## Why does the tool description matter?

The model decides when to call a tool from its description. Say what it does and when to use it.

## Is the generator free?

Yes. It runs in your browser with no account and no limit.

## Related tools

- /free-tools/mcp-config-generator
- /free-tools/token-counter
- /free-tools/llms-txt-generator

## Last reviewed

2026-10-14.