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

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GitHub - kioie/toolschema-kit · GitHub

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toolschema-kit

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ToolSchema Kit

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 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.

What this is

A small commerce-catalog MCP server (Go, tinymcp) 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)

Live endpoint

https://toolschema-kit.onrender.com/mcp

(Also: GET /health for liveness.)

Quick start

git clone https://github.com/kioie/toolschema-kit.git<br>cd toolschema-kit<br>CATALOG_MCP_TRANSPORT=http go run ./cmd/catalog-mcp<br># MCP: http://127.0.0.1:8080/mcp

Bump schema (diff exercise)

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.

Cursor / Claude Desktop

mcp.json.example — point url at localhost or the live host above.

Production monitoring

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 coverage assert as an optional gate — swap in your own checker if you prefer.

Docs

Guide<br>Topic

docs/end-to-end.md<br>Local → agent → diff → optional watch

docs/ci.md<br>GitHub Actions contract coverage

docs/simulate-drift.md<br>Version bumps & silent drift

docs/comparison.md<br>OpenAPI diff vs MCP tool-schema diff

Deploy

Target<br>Command / file

Render<br>Blueprint render.yaml — auto-deploy on push when connected

Container<br>docker run -p 8080:8080 ghcr.io/kioie/toolschema-kit:latest

Fly<br>fly.toml + optional workflow (needs billing)

Keywords

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.

License

MIT — see LICENSE.

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toolschema catalog docs diff contract drift

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