MCP Tool Schema Validator
Validate MCP tool definitions and verify `inputSchema` before deployment
MCP Tool Definition
Formatted Definition
Validate MCP tool definitions before they ship
MCP tool definitions need to be valid JSON, expose the right fields, and carry an inputSchema that's itself valid JSON Schema. Validating them locally catches typos, missing fields, and schema mistakes before the tool is exposed to a model — which is much cheaper than debugging tool calls at runtime.
Use the validator when you need to
Check an MCP tool definition before publishing
Catch missing fields, malformed inputSchema, and JSON Schema typos before your server exposes the tool.
Audit a third-party MCP server
Verify someone else's tool definitions follow the spec before integrating with their server.
Triage tool-call failures
When a model misuses a tool, validate the definition first to rule out a malformed schema as the cause.
How to validate an MCP tool
- 1
Paste the full MCP tool definition (not just the inputSchema).
- 2
Click Validate to check structure, required fields, and the embedded JSON Schema.
- 3
Fix reported errors and warnings, then re-validate before publishing.
Keep going
Build the inputSchema
Generate the inputSchema from a sample before validating the full tool object.
Anthropic equivalent
Adapt the same input shape into a Claude tool definition.
Validate the schema directly
Run JSON Schema validation on the inputSchema in isolation.
Test the MCP endpoint
Send a real request once the tool definition validates cleanly.
Common MCP validation workflows
Run every tool definition through validation before shipping the server.
Validate someone else's MCP server definitions before wiring an agent to them.
When a model fails to call a tool correctly, check the definition for warnings before debugging the model.
Herramientas relacionadas
Structured Output Schema Builder
Generate OpenAI, Anthropic, MCP, or plain JSON Schema wrappers from sample output
Anthropic Tool Input Builder
Build Claude tool definitions with `input_schema` from sample JSON input
Validador JSON Schema
Valida documentos JSON contra un JSON Schema
Explorador de API
Prueba APIs REST en el navegador con respuestas JSON formateadas
Preguntas frecuentes
It checks that your tool definition is valid JSON, confirms the required top-level fields are present, validates the embedded `inputSchema`, and reports both errors and warnings about the MCP shape.
No. It validates the JSON definition locally in your browser. It does not connect to a running MCP server or any third-party API.
Typical issues include missing `name`, a non-object `inputSchema`, invalid JSON Schema inside `inputSchema`, non-boolean annotation hints, and definitions that omit a useful description.
Yes. Paste the entire MCP tool definition, not only the `inputSchema`. The validator is designed to inspect the full object.