i fell asleep in physics class learning about fuses and ended up building a circuit breaker for runaway llm tool loops

So last month I was sitting in a super boring physics lecture. The professor was drawing copper wires and talking about how electrical fuses melt when current gets out of control so the whole house doesn't burn down.

Naturally my brain drifted to what happened to me two days prior when I left an autonomous agent running while getting coffee. The agent got stuck in a loop calling read_file with the exact same parameters 47 times in a row. When using frontier cloud models like GPT-4o or Claude Sonnet, those runaway loops get expensive as fuck real fast.

That night I realized LLM frameworks have zero real-time circuit breakers. Sure, you can set max_iterations = 25, but that only stops the agent after it already wasted 24 useless tool calls and burned your API budget. What if your agent calls the exact same tool with the exact same parameters 5 times in 10 seconds? Why let it keep burning tokens?

So I built moven (and made it open source).

It's a lightweight synchronous wrapper for your agent tools (moven-sdk). It sits right in the hot path of tool executions and evaluates 5 rules in under 1ms before the tool even runs:

1. Sliding window repeat shield — if an agent invokes the same tool with identical arguments 5 times in 60s, it instantly trips the fuse.
2. Cost limit ceiling — calculates real-time token cost per model and pulls the plug if a single run exceeds your dollar threshold (e.g. $1.50).
3. Recursion depth guard — limits nested sub-agent calls.
4. No-progress state hash — hashes output states to detect when an agent is repeating itself without making actual progress.
5. Cheaper model fallback — when a loop is detected, instead of killing the agent outright, it can automatically rerun the turn using a 90% cheaper model (like Gemini Flash or Llama 8b).

You can try it out directly at moven.dev or set it up in your existing project by running, which has a nice CLI onboarding to auto install:

npx moven-ai-cli init

Or just install the SDK directly:

npm install moven-sdk

It works 100% locally with zero backend dependencies if you want to keep everything offline, or you can check out the web dashboard at moven.dev to get live telemetry traces and time-travel replay.

Code is open source on GitHub:

• SDK: https://github.com/Moven-AI/moven-node-sdk
• CLI: https://github.com/Moven-AI/Moven-CLI
• Web dashboard & replay engine: https://moven.dev

Would love to hear what you guys think, or if you've ever had an agent go rogue and eat your credit card/GPU fans. Feedback and roasting appreciated!