Module validation 

Opt-in JSON Schema validation of tool inputs and outputs.

The MCP Tools spec requires servers to validate tools/call arguments against each tool’s inputSchema, and—when a tool declares an outputSchema—to return structuredContent conforming to it. mcpkit’s generic ToolHandler path is an unchecked escape hatch: it receives raw JSON and returns arbitrary JSON. This module provides an opt-in ValidatingToolHandler decorator that enforces those schemas.

Because it wraps the ToolHandler itself, it covers every dispatch path uniformly—normal tools/call, task-augmented background execution, and the HTTP adapters—since they all funnel through ToolHandler::call_tool.

Per the spec’s error-handling section, arguments that fail a tool’s inputSchema are reported as a tool-execution error (isError: true), not a JSON-RPC protocol error; malformed request envelopes and unknown tools remain protocol errors and are handled upstream. An outputSchema violation is a server-side bug: it is logged, the invalid structuredContent is dropped, and the call returns isError: true.

This module is gated behind the schema-validation feature.

Structs

ValidatingToolHandler

A ToolHandler decorator that validates tool inputs and/or outputs against their declared JSON Schemas.

ValidationMode

Which directions ValidatingToolHandler enforces.

Functions

validate_json

Validate instance against JSON Schema schema, returning the list of violation messages (empty Ok means valid).