MCP Tool Response Schema Builder

Define what your MCP tool returns using a visual form. Build success and error response schemas with typed fields, nullable flags, enums, and example values. Outputs JSON Schema and TypeScript types.

Tool Details

Tool name

Success description

Return value is an array

Response Fields 0 defined

ReqNull

Error Response Shape

Configure what your error responses include. A success: false field is always included.

Include error code

Machine-readable code like NOT_FOUND, INVALID_INPUT

Include error message

Human-readable description

Include details object

Optional extra context object

Extra error fields (comma-separated)

{
  "type": "object",
  "properties": {},
  "additionalProperties": false
}

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Response Schema Design Guide

✅

Always include a success indicator

Add a boolean "success: true" field so callers can check the response type without inspecting the entire payload.

🚫

Define your error shape explicitly

At minimum: error code (machine-readable) + message (human-readable). Consistent error shapes make agent error handling predictable.

📝

Describe every field

The AI model reads field descriptions to understand what it received. "The user's ISO 8601 join date" is far more useful than "date".

🔢

Use enum for fixed-value fields

Status fields like "open", "closed", "pending" should be enums so the model knows all valid values when reasoning about the response.

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Frequently Asked Questions

What is an MCP tool response schema?

An MCP tool response schema is the JSON Schema or TypeScript type that describes what a tool returns when called. While MCP tools have a well-defined inputSchema, the response shape is up to the tool author. Documenting it explicitly helps the AI model understand what it received and how to use the data.

How is this different from inputSchema?

inputSchema defines what the tool accepts (arguments). The response schema defines what the tool returns (output). Both are part of a complete tool contract. The MCP Input Schema Builder covers inputs — this tool covers outputs.

What is the "Full (oneOf)" output?

The Full schema combines both success and error schemas into a JSON Schema oneOf union — a single schema that validates either a success response or an error response. Useful when you want to document the complete contract in one schema.

What does "nullable" mean for a field?

Marking a field as nullable means its JSON Schema type becomes an array like ["string", "null"] instead of just "string". This allows the field to be either its normal type or null — common for optional fields that are explicitly absent.

Is my data uploaded anywhere?

No. This tool runs entirely in your browser. Nothing is uploaded or stored.

MCP Tools