Langchain Tutorial #7: Stop Infinite Loops! Model Call Limits Middleware | Cost Control | Guardrail

About this lesson

Stop burning your budget on runaway AI agents! 🚀 In this video, we dive deep into a critical middleware for LangChain and LangGraph developers: Model Call Limits. When building AI agents that use multiple tools, it’s easy for a model to get stuck in an infinite loop or for a user session to rack up unnecessary costs. We explore how to implement guardrails using three key properties: Thread Limit: Restrict the total number of model calls across an entire conversation thread. Run Limit: Control the maximum number of internal model calls allowed for a single request (perfect for preventing tool-calling loops). Exit Behavior: Choose between a graceful "End" (returning the current state) or an "Error" (triggering an exception). What’s inside this tutorial: ✅ Why you need model call limits for system stability. ✅ Setting up the Middleware in your notebook. ✅ Real-world demos: Testing thread_limit with simple math queries. ✅ Preventing tool-looping: Testing run_limit with a multi-country weather tool scenario. ✅ Comparing "End" vs "Error" exit behaviors. By the end of this video, you'll know how to protect your API keys and ensure your AI applications remain stable and cost-effective. Tools Used: LangChain / LangGraph Python Notebooks Google Antigravity IDE Timestamps (Suggested) 0:00 - Introduction to Model Call Limits 0:45 - Scenario 1: Managing Long Threads & Costs 1:20 - Scenario 2: Preventing Infinite Tool Loops 2:10 - Middleware Properties: Thread Limit, Run Limit, & Exit Behavior 3:45 - Code Walkthrough: Implementing Thread Limits 5:30 - Testing "End" vs "Error" Exit Behaviors 7:15 - Deep Dive: Using Run Limits with Tools (Weather Example) 9:40 - Summary & Best Practices Github: https://github.com/NajiAboo/langchain-v1/blob/main/01-middleware/model_call_limit.ipynb LangChain, LangGraph, AI Agents, LLM Middleware, Model Call Limits, AI Cost Optimization, Python AI Tutorial, LangChain Tutorial, Prevent Infinite Loops AI, LangGraph Middleware, Agen

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