agentbrake-sdk 0.1.1

The emergency brake for multi-agent systems. Stop runaway LangChain & CrewAI agents in real time — before 50 cents becomes $47,000.

🛑 AgentBrake

The emergency brake for multi-agent systems. Stop runaway LangChain & CrewAI agents in real time — before 50 cents turns into $47,000.

pip install agentbrake-sdk

The install name is agentbrake-sdk; you import it as agentbrake.

A real LangChain (LangGraph) agent caught in a loop — stopped at step 3, before the bill grows. Run it yourself, no API key needed.

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The problem

In November 2025, four LangChain agents entered an infinite loop. They ran for 11 days. The bill was $47,000. Nobody noticed until it was over.

This is not rare. Autonomous agents fail expensively rather than loudly:

• An agent calls the same tool 14,000 times with identical arguments.
• A planner expands one simple task into dozens of high-context subagent calls.
• A reasoning loop never hits its stopping condition and runs all night.

Observability tools record this. They don't stop it. By the time the alert fires — or someone reads it — the money is gone. The gap between "the alert fired" and "the run stopped" is exactly where the damage compounds.

AgentBrake closes that gap. It intercepts, not just observes.

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How it works

AgentBrake hooks into your agent's execution and watches every step in real time. When a run crosses a limit you set, it raises a clean exception that halts the agent before the next expensive call goes out.

from agentbrake import LangChainBrakeMiddleware
from langchain.agents import create_agent

agent = create_agent(
    model, tools=tools,
    middleware=[LangChainBrakeMiddleware(max_cost_usd=2.00, repeat_tool_limit=5)],
)

That's it. One line.

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What it catches

Runaway pattern	How AgentBrake stops it
Identical-tool loops (same call, same args, over and over)	repeat_tool_limit — trips after N identical calls in a row
Cost blowouts (the $47k overnight run)	max_cost_usd — a hard ceiling, enforced live as tokens are spent
Endless reasoning (no stopping condition)	max_steps — caps total reasoning steps
Tool-call storms	max_tool_calls — caps total tool invocations
Hung runs	max_duration_s — wall-clock ceiling

It warns at 80% of any limit, and stops at 100%.

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LangChain

LangChain has two agent stacks, and they intercept differently — AgentBrake ships the right tool for each.

LangChain 1.x (create_agent / LangGraph) — use the middleware. It runs inside the agent graph, so it can actually halt the run:

from agentbrake import LangChainBrakeMiddleware, AgentBrakeError
from langchain.agents import create_agent

agent = create_agent(
    model, tools=tools,
    middleware=[LangChainBrakeMiddleware(max_cost_usd=2.00, repeat_tool_limit=5, max_steps=30)],
)

try:
    agent.invoke({"messages": [("user", "...")]})
except AgentBrakeError as e:
    print(f"Stopped safely: {e.reason}")

Classic AgentExecutor (LangChain 0.x) — use the callback:

from agentbrake import LangChainBrake, AgentBrakeError

brake = LangChainBrake(
    max_cost_usd=2.00,
    repeat_tool_limit=5,
    max_steps=30,
)

try:
    agent_executor.invoke({"input": "..."}, config={"callbacks": [brake]})
except AgentBrakeError as e:
    print(f"Stopped safely: {e.reason}")

CrewAI

from agentbrake import CrewAIBrake, AgentBrakeError

CrewAIBrake(max_cost_usd=3.00, repeat_tool_limit=5).install()

try:
    crew.kickoff()
except AgentBrakeError as e:
    print(f"Crew stopped safely: {e.reason}")

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Live cost visibility

Every run prints where your money is going, step by step:

[AgentBrake] step 1: web_search · running cost $0.0080
[AgentBrake] step 2: web_search · running cost $0.0160
[AgentBrake] ⚠️  approaching cost limit (1.60 of 2.00)
[AgentBrake] 🛑 STOPPED — loop detected: same tool call repeated 5× in a row
  steps=5 tool_calls=5 llm_calls=4 tokens=9,200 cost=$0.032 elapsed=0.4s

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Pricing built in

AgentBrake ships with current pricing for GPT-4o, GPT-4, Claude (Opus/Sonnet/Haiku), and Gemini, so cost ceilings work out of the box. Override anytime with your own rates.

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Why not just set a provider spend cap?

Provider caps are monthly and account-wide — they fire after the damage, across everything. AgentBrake is per-run and in-process — it stops this agent now, before the next call. It's the difference between a smoke alarm and a sprinkler.

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License

MIT — free to use, including commercially.