Schema Sieve is a local MCP tool for understanding JSON Schema files while planning tests. It focuses on the part that usually takes the most time: finding required paths, nested constraints, unions, arrays, and likely sensitive fields before writing fixtures.

Tools

inspect_schema: summarize types, properties, required fields, constraints, composition, and references.
plan_fixture: produce placeholder paths such as <string>, <integer>, and <string:date-time> without inventing or copying test data.

Safety

Only local JSON files are accepted.
Paths are bounded by SCHEMA_SIEVE_ROOT, which defaults to the workspace parent when launched from the package.
Files are capped at 2 MB and results are bounded.
Examples, defaults, constants, and sensitive-like property names are omitted or marked as omitted.
This is structural guidance, not a JSON Schema validator and not a security scanner.

Run

npm install
npm run build
node dist/index.js

Quick start

npm install
npm run build
node dist/index.js

The server uses stdio, so it can be connected to Claude Desktop, Cursor, VS Code, MCP Inspector, or another compatible MCP client.

Tools at a glance

inspect_schema: Summarize a local JSON Schema
plan_fixture: Create a privacy-safe placeholder plan for test fixture fields in a local JSON Schema. It does not fabricate or copy example data.

Try it

After building, connect the server through your MCP client. The repository root also contains smoke-test.mjs for projects covered by the shared harness. A typical tool call starts with inspect_schema.