If you've built anything with LangGraph past the demo stage, you've probably had the same uneasy moment I did. The agent works, it's calling tools, it's doing real things, and then you realize the only thing stopping it from doing the wrong real thing is a line in the prompt that says "please don't."
A prompt isn't a control. The agent can be talked into ignoring it, some upstream input can steer it somewhere you didn't expect, and either way the tool call just runs. Once that tool call can move money, hit prod, or touch customer data, "the model seemed confident" isn't where you want your safety to live.
So here's how to put a real check in front of the tool call instead. I'll use Faramesh, the open source thing I've been building for exactly this. It's a local daemon that sits in front of your agent's tool calls and returns permit / deny / defer based on a policy you write. No LLM in the decision path, so the same call always gets the same answer.
The whole thing takes about 10 minutes. Every command below is copy-pasteable. I'll be clear about the one or two spots where you swap in your own stuff.
How it works in one picture
