# Docs by LangChain: Open source (Python)

> Markdown index of the Open source (Python) documentation.

## Open source (Python)

- [Memory](https://docs.langchain.com/oss/python/langgraph/add-memory.md)
- [Build a custom RAG agent with LangGraph](https://docs.langchain.com/oss/python/langgraph/agentic-rag.md)
- [Application structure](https://docs.langchain.com/oss/python/langgraph/application-structure.md)
- [Backward compatibility](https://docs.langchain.com/oss/python/langgraph/backward-compatibility.md)
- [Case studies](https://docs.langchain.com/oss/python/langgraph/case-studies.md)
- [Changelog](https://docs.langchain.com/oss/python/langgraph/changelog-js.md)
- [Changelog](https://docs.langchain.com/oss/python/langgraph/changelog-py.md)
- [Checkpointers](https://docs.langchain.com/oss/python/langgraph/checkpointers.md)
- [Choosing between Graph and Functional APIs](https://docs.langchain.com/oss/python/langgraph/choosing-apis.md)
- [Deployment](https://docs.langchain.com/oss/python/langgraph/deploy.md)
- [GRAPH_RECURSION_LIMIT](https://docs.langchain.com/oss/python/langgraph/errors/GRAPH_RECURSION_LIMIT.md)
- [INVALID_CHAT_HISTORY](https://docs.langchain.com/oss/python/langgraph/errors/INVALID_CHAT_HISTORY.md)
- [INVALID_CONCURRENT_GRAPH_UPDATE](https://docs.langchain.com/oss/python/langgraph/errors/INVALID_CONCURRENT_GRAPH_UPDATE.md)
- [INVALID_GRAPH_NODE_RETURN_VALUE](https://docs.langchain.com/oss/python/langgraph/errors/INVALID_GRAPH_NODE_RETURN_VALUE.md)
- [MISSING_CHECKPOINTER](https://docs.langchain.com/oss/python/langgraph/errors/MISSING_CHECKPOINTER.md)
- [MULTIPLE_SUBGRAPHS](https://docs.langchain.com/oss/python/langgraph/errors/MULTIPLE_SUBGRAPHS.md)
- [Event streaming](https://docs.langchain.com/oss/python/langgraph/event-streaming.md)
- [Fault tolerance](https://docs.langchain.com/oss/python/langgraph/fault-tolerance.md)
- [Custom stream channels](https://docs.langchain.com/oss/python/langgraph/frontend/custom-stream-channels.md)
- [Graph execution](https://docs.langchain.com/oss/python/langgraph/frontend/graph-execution.md)
- [Overview](https://docs.langchain.com/oss/python/langgraph/frontend/overview.md)
- [Functional API overview](https://docs.langchain.com/oss/python/langgraph/functional-api.md)
- [Graph API overview](https://docs.langchain.com/oss/python/langgraph/graph-api.md)
- [Install LangGraph](https://docs.langchain.com/oss/python/langgraph/install.md)
- [Interrupts](https://docs.langchain.com/oss/python/langgraph/interrupts.md)
- [Run a local server](https://docs.langchain.com/oss/python/langgraph/local-server.md)
- [LangSmith Observability](https://docs.langchain.com/oss/python/langgraph/observability.md)
- [LangGraph overview](https://docs.langchain.com/oss/python/langgraph/overview.md)
- [Persistence](https://docs.langchain.com/oss/python/langgraph/persistence.md)
- [LangGraph runtime](https://docs.langchain.com/oss/python/langgraph/pregel.md)
- [Quickstart](https://docs.langchain.com/oss/python/langgraph/quickstart.md)
- [Build a custom SQL agent](https://docs.langchain.com/oss/python/langgraph/sql-agent.md)
- [Stores](https://docs.langchain.com/oss/python/langgraph/stores.md)
- [Streaming](https://docs.langchain.com/oss/python/langgraph/streaming.md)
- [LangSmith Studio](https://docs.langchain.com/oss/python/langgraph/studio.md)
- [Test](https://docs.langchain.com/oss/python/langgraph/test.md)
- [Thinking in LangGraph](https://docs.langchain.com/oss/python/langgraph/thinking-in-langgraph.md)
- [Agent Chat UI](https://docs.langchain.com/oss/python/langgraph/ui.md)
- [Use the functional API](https://docs.langchain.com/oss/python/langgraph/use-functional-api.md)
- [Use the graph API](https://docs.langchain.com/oss/python/langgraph/use-graph-api.md)
- [Subgraphs](https://docs.langchain.com/oss/python/langgraph/use-subgraphs.md)
- [Use time-travel](https://docs.langchain.com/oss/python/langgraph/use-time-travel.md)
- [Workflows and agents](https://docs.langchain.com/oss/python/langgraph/workflows-agents.md)