# Docs by LangChain: Open source (Python)

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

## Open source (Python)

- [LangChain Academy](https://docs.langchain.com/oss/python/langchain/academy.md)
- [Agents](https://docs.langchain.com/oss/python/langchain/agents.md)
- [Changelog](https://docs.langchain.com/oss/python/langchain/changelog-js.md)
- [Changelog](https://docs.langchain.com/oss/python/langchain/changelog-py.md)
- [Component architecture](https://docs.langchain.com/oss/python/langchain/component-architecture.md)
- [Context engineering in agents](https://docs.langchain.com/oss/python/langchain/context-engineering.md)
- [Build a data analysis agent from scratch](https://docs.langchain.com/oss/python/langchain/deep-agent-from-scratch.md)
- [Deployment](https://docs.langchain.com/oss/python/langchain/deploy.md)
- [INVALID_PROMPT_INPUT](https://docs.langchain.com/oss/python/langchain/errors/INVALID_PROMPT_INPUT.md)
- [INVALID_TOOL_RESULTS](https://docs.langchain.com/oss/python/langchain/errors/INVALID_TOOL_RESULTS.md)
- [MESSAGE_COERCION_FAILURE](https://docs.langchain.com/oss/python/langchain/errors/MESSAGE_COERCION_FAILURE.md)
- [MODEL_AUTHENTICATION](https://docs.langchain.com/oss/python/langchain/errors/MODEL_AUTHENTICATION.md)
- [MODEL_NOT_FOUND](https://docs.langchain.com/oss/python/langchain/errors/MODEL_NOT_FOUND.md)
- [MODEL_RATE_LIMIT](https://docs.langchain.com/oss/python/langchain/errors/MODEL_RATE_LIMIT.md)
- [OUTPUT_PARSING_FAILURE](https://docs.langchain.com/oss/python/langchain/errors/OUTPUT_PARSING_FAILURE.md)
- [Event streaming](https://docs.langchain.com/oss/python/langchain/event-streaming.md)
- [Branching chat](https://docs.langchain.com/oss/python/langchain/frontend/branching-chat.md)
- [Controlled generative UI](https://docs.langchain.com/oss/python/langchain/frontend/controlled-generative-ui.md)
- [Declarative generative UI](https://docs.langchain.com/oss/python/langchain/frontend/declarative-generative-ui.md)
- [Generative UI overview](https://docs.langchain.com/oss/python/langchain/frontend/generative-ui-overview.md)
- [Headless tools](https://docs.langchain.com/oss/python/langchain/frontend/headless-tools.md)
- [Human-in-the-Loop](https://docs.langchain.com/oss/python/langchain/frontend/human-in-the-loop.md)
- [AI Elements](https://docs.langchain.com/oss/python/langchain/frontend/integrations/ai-elements.md)
- [assistant-ui](https://docs.langchain.com/oss/python/langchain/frontend/integrations/assistant-ui.md)
- [CopilotKit](https://docs.langchain.com/oss/python/langchain/frontend/integrations/copilotkit.md)
- [OpenUI](https://docs.langchain.com/oss/python/langchain/frontend/integrations/openui.md)
- [Overview](https://docs.langchain.com/oss/python/langchain/frontend/integrations/overview.md)
- [Join & rejoin streams](https://docs.langchain.com/oss/python/langchain/frontend/join-rejoin.md)
- [Markdown messages](https://docs.langchain.com/oss/python/langchain/frontend/markdown-messages.md)
- [Message queues](https://docs.langchain.com/oss/python/langchain/frontend/message-queues.md)
- [Open-ended generative UI](https://docs.langchain.com/oss/python/langchain/frontend/open-ended-generative-ui.md)
- [Overview](https://docs.langchain.com/oss/python/langchain/frontend/overview.md)
- [Reasoning tokens](https://docs.langchain.com/oss/python/langchain/frontend/reasoning-tokens.md)
- [Structured output](https://docs.langchain.com/oss/python/langchain/frontend/structured-output.md)
- [Time travel](https://docs.langchain.com/oss/python/langchain/frontend/time-travel.md)
- [Tool calling](https://docs.langchain.com/oss/python/langchain/frontend/tool-calling.md)
- [Get help](https://docs.langchain.com/oss/python/langchain/get-help.md)
- [Guardrails](https://docs.langchain.com/oss/python/langchain/guardrails.md)
- [Human-in-the-loop](https://docs.langchain.com/oss/python/langchain/human-in-the-loop.md)
- [Install LangChain](https://docs.langchain.com/oss/python/langchain/install.md)
- [Build a semantic search engine with LangChain](https://docs.langchain.com/oss/python/langchain/knowledge-base.md)
- [Long-term memory](https://docs.langchain.com/oss/python/langchain/long-term-memory.md)
- [Model Context Protocol (MCP)](https://docs.langchain.com/oss/python/langchain/mcp.md)
- [Messages](https://docs.langchain.com/oss/python/langchain/messages.md)
- [Prebuilt middleware](https://docs.langchain.com/oss/python/langchain/middleware/built-in.md)
- [Custom middleware](https://docs.langchain.com/oss/python/langchain/middleware/custom.md)
- [Overview](https://docs.langchain.com/oss/python/langchain/middleware/overview.md)
- [Models](https://docs.langchain.com/oss/python/langchain/models.md)
- [Custom workflow](https://docs.langchain.com/oss/python/langchain/multi-agent/custom-workflow.md)
- [Build customer support with handoffs](https://docs.langchain.com/oss/python/langchain/multi-agent/handoffs-customer-support.md)
- [Handoffs](https://docs.langchain.com/oss/python/langchain/multi-agent/handoffs.md)
- [Multi-agent](https://docs.langchain.com/oss/python/langchain/multi-agent/index.md)
- [Build a multi-source knowledge base with routing](https://docs.langchain.com/oss/python/langchain/multi-agent/router-knowledge-base.md)
- [Router](https://docs.langchain.com/oss/python/langchain/multi-agent/router.md)
- [Build a SQL assistant with on-demand skills](https://docs.langchain.com/oss/python/langchain/multi-agent/skills-sql-assistant.md)
- [Skills](https://docs.langchain.com/oss/python/langchain/multi-agent/skills.md)
- [Build a personal assistant with subagents](https://docs.langchain.com/oss/python/langchain/multi-agent/subagents-personal-assistant.md)
- [Subagents](https://docs.langchain.com/oss/python/langchain/multi-agent/subagents.md)
- [LangSmith Observability](https://docs.langchain.com/oss/python/langchain/observability.md)
- [LangChain overview](https://docs.langchain.com/oss/python/langchain/overview.md)
- [Philosophy](https://docs.langchain.com/oss/python/langchain/philosophy.md)
- [Quickstart](https://docs.langchain.com/oss/python/langchain/quickstart.md)
- [Retrieval](https://docs.langchain.com/oss/python/langchain/retrieval.md)
- [Runtime](https://docs.langchain.com/oss/python/langchain/runtime.md)
- [Short-term memory](https://docs.langchain.com/oss/python/langchain/short-term-memory.md)
- [Build a SQL agent](https://docs.langchain.com/oss/python/langchain/sql-agent.md)
- [Streaming](https://docs.langchain.com/oss/python/langchain/streaming.md)
- [Structured output](https://docs.langchain.com/oss/python/langchain/structured-output.md)
- [LangSmith Studio](https://docs.langchain.com/oss/python/langchain/studio.md)
- [Agent Evals](https://docs.langchain.com/oss/python/langchain/test/evals.md)
- [Test](https://docs.langchain.com/oss/python/langchain/test/index.md)
- [Integration testing](https://docs.langchain.com/oss/python/langchain/test/integration-testing.md)
- [Unit testing](https://docs.langchain.com/oss/python/langchain/test/unit-testing.md)
- [Tools](https://docs.langchain.com/oss/python/langchain/tools.md)
- [Agent Chat UI](https://docs.langchain.com/oss/python/langchain/ui.md)
- [Build a voice agent with LangChain](https://docs.langchain.com/oss/python/langchain/voice-agent.md)