Tool call & MCP schema builder

One schema, four wrappers

Every provider describes tools with the same core: a JSON Schema object listing your parameters. What differs is the envelope. OpenAI wraps it as function.parameters inside a type: "function" object, Anthropic calls it input_schema, and an MCP tool schema uses camel-cased inputSchema in its tools/list response. Hand-porting a function calling schema between those envelopes is where typos creep in, so this builder generates all four from one definition.

The classic mistakes are structural, not syntactic. Forgetting the requiredarray makes every parameter optional, so models happily omit the one argument your code depends on. Describing a fixed set of options in prose ("must be celsius or fahrenheit") instead of a proper enuminvites free-form values you then have to re-validate. And vague parameter descriptions are the top cause of bad tool calls — the description is the model's only documentation. This builder keeps each MCP tool schema strictly valid: enums become { type: "string", enum: [...] }, lists become typed arrays, and the required array is always present.

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