ToolSchema Kit – reproducible MCP contract drift lab (10-min tutorial)

ToolSchema Kit, a new open-source repository, provides a reproducible MCP contract drift lab for agent platforms like Cursor and Claude Desktop, enabling teams to detect silent breaking changes in tool schemas. The kit includes a commerce-catalog MCP server and CI workflows for scheduled contract monitoring, applying OpenAPI-style diffing to MCP tools/list and tool I/O schemas.

MCP tool-schema reference & contract exercises for agent platforms Cursor, Claude Desktop, custom runtimes . If you already gate OpenAPI breaking changes with tools like OASDiff https://github.com/Tufin/oasdiff or policy checks in the spirit of SpecShield , this repo applies the same mindset to tools/list and tool I/O schemas — where HTTP can stay 200 while agent contracts still break.A small commerce-catalog MCP server Go, tinymcp https://github.com/kioie/tiny-go-mcp-server you can run locally, in CI, or on a free host. It exposes get product and list skus with versioned output controlled by CATALOG SCHEMA VERSION . Use it to: - Prototype agent flows against a stable catalog contract - Reproduce silent drift healthy HTTP, changed tool schemas - Optional: assert every URL in mcp.json is covered by an external watch see CI /kioie/toolschema-kit/blob/master/docs/ci.md https://toolschema-kit.onrender.com/mcp Also: GET /health for liveness. git clone https://github.com/kioie/toolschema-kit.git cd toolschema-kit CATALOG MCP TRANSPORT=http go run ./cmd/catalog-mcp MCP: http://127.0.0.1:8080/mcp CATALOG SCHEMA VERSION=2026.06.02 CATALOG MCP TRANSPORT=http go run ./cmd/catalog-mcp Compare tools/list or tool outputs before/after — same idea as an OpenAPI diff, for MCP. mcp.json.example /kioie/toolschema-kit/blob/master/mcp.json.example — point url at localhost or the live host above.Teams usually run a scheduled contract watch on MCP URLs diff tools/list , alert on breaking changes . This repo stays vendor-neutral; one workflow shows DriftGuard https://driftguard.org coverage assert as an optional gate — swap in your own checker if you prefer. | Guide | Topic | |---|---| | docs/ci.md /kioie/toolschema-kit/blob/master/docs/ci.md docs/simulate-drift.md /kioie/toolschema-kit/blob/master/docs/simulate-drift.md docs/comparison.md /kioie/toolschema-kit/blob/master/docs/comparison.md | Target | Command / file | |---|---| Render | Blueprint render.yaml | Container docker run -p 8080:8080 ghcr.io/kioie/toolschema-kit:latest Fly + optional workflow needs billing /kioie/toolschema-kit/blob/master/fly.toml fly.toml MCP schema drift, tool-schema diff, OpenAPI-style breaking changes for agents, Cursor MCP contract test, tools/list monitoring, silent API drift, SpecShield alternative MCP, OASDiff for MCP. MIT — see LICENSE /kioie/toolschema-kit/blob/master/LICENSE .