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

> Source: <https://github.com/kioie/toolschema-kit>
> Published: 2026-06-17 21:04:42+00:00

**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).