LangChain Cheat Sheet

This content was generated with the assistance of AI and should be verified against the official documentation of each tool and framework before being relied on in production.

This section’s bibliography lists the reference material consulted while preparing these pages.

A single-page index of quick back-links to every page in this sub-section, grouped the same way as the sub-section itself — handy for jumping straight to the topic you need instead of paging through the full navigation. It was written against langchain 1.4.3, langchain-core 1.6.5, langgraph 1.2.12 and langsmith 0.14.1 on Python 3.12, langchain 1.5.14 and @langchain/langgraph 1.4.18 on npm, and LangChain4j 1.20.2 (1.20.2-beta30 for the agentic and MCP modules) on Java 21, all checked on 2026-09-29; the full table is the version baseline on the landing page.

The downloadable PDF is a separate, single A4 page meant for printing. It states the version baseline this sub-section targets and covers:

  • the package-to-import table for LangChain v1;

  • chat-model and structured-output one-liners;

  • the @tool decorator;

  • create_agent and the middleware hooks;

  • a StateGraph skeleton and reducers;

  • checkpointer and store setup;

  • interrupt and Command;

  • the stream modes;

  • the MCP adapter snippet;

  • the LangSmith environment variables and an evaluation snippet;

  • the langgraph CLI;

  • the LangChain4j AiServices, @Tool, memory and agentic equivalents;

  • the LangChain.js equivalents.

Overview — LangChain.

Core LangChain — Ecosystem & Packages, Chat Models & Messages, Prompts & Templates, LCEL & Runnables, Structured Output and Tools.

Agents — Agents with create_agent and Middleware.

LangGraph — LangGraph Fundamentals, LangGraph Workflows, Short-Term Memory & Checkpointers, Long-Term Memory Stores, Human-in-the-Loop & Time Travel, Streaming and Multi-Agent & Deep Agents.

Integrations — MCP Adapters, Retrieval & RAG Bridge, Multimodality & Voice, Guardrails & Security and Local Models.

LangSmith — Observability with LangSmith, Evaluation, Testing and Deployment.

Other languages — LangChain.js, LangChain4j and LangChain4j Agents & MCP.

Download the LangChain Cheat Sheet (PDF)

References

The PDF summarizes the official documentation; each source is cited in full on the page listed above that covers it, and in LangChain’s bibliography.