A few days ago I posted about a problem I hit with MCP tool schema drift.

The short version:

An MCP server changed a parameter from location to city .

My agent kept sending location .

Nothing warned me before runtime.

That first version of MCP Sentinel was just the basic idea:

sentinel init sentinel snapshot sentinel check sentinel diff

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Since then, I shipped MCP Sentinel v1.0.0 .

GitHub:

https://github.com/Wannavf/mcp-sentinel

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npm:

npm install -g @wannavf/mcp-sentinel

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The framing changed a bit

The original problem was annoying because it broke my tools silently.

But after feedback, I think the bigger point is this:

MCP tool schemas are contracts.

If a tool changes its parameters, required fields, enum values, return shape, or descriptions, that is not just a small implementation detail.

It changes what an agent can ask for.

It can also change when the agent…