Como usar
- Copie o comando e verifique o pacote antes de instalar no seu ambiente de agente.
- Consulte no original as ferramentas, credenciais e ambientes necessários.
- Descreva os dados de entrada e a entrega esperada; confira a saída com as fontes.
npx skills add https://github.com/magnus919/agent-skills --skill langchainAntes de começar
- A instalação não inclui assinatura de modelo, franquia API ou acesso aos seus arquivos.
- Estrelas e instalações indicam atividade, não um teste independente de qualidade ou segurança.
Documento original do Skill
Renderizado do repositório de origem, preservando títulos, exemplos, código, tabelas, links e imagens.
LangChain Expert Skill
LangChain is an MIT-licensed Python framework for building LLM-powered applications. Since v1.0 (October 2025), it provides a layered architecture: high-level chain composition via LCEL (LangChain Expression Language), agent creation via create_agent (running on the LangGraph runtime underneath), and production observability via LangSmith. With 1000+ integrations and 100K+ GitHub stars, it is the most widely adopted LLM orchestration framework.
Key v1.0 change: All new LangChain agents run on the LangGraph runtime. AgentExecutor is in maintenance mode until December 2026. Use create_agent for new agents. Drop to LangGraph directly when you need full state-machine control.
⚠️ CRITICAL: Do NOT use AgentExecutor for new code. It is in maintenance mode until December 2026. Use create_agent(model, tools, prompt) instead — it generates a LangGraph state machine with streaming, persistence, and observability out of the box.Core Principles
These principles govern every decision when building with LangChain. Read them before proceeding to the reference guides.
- LCEL is the composition primitive. The pipe operator (
|) chains Runnables. Every component — prompt, model, parser, retriever — implements the Runnable interface. Build everything in LCEL. - Agents run on LangGraph. Since v1.0,
create_agentgenerates a LangGraph state machine underneath. You get streaming, persistence, and observability without writing graph code. Drop to LangGraph when you need branching, cycles, or human-in-the-loop. - RAG is a chain, not a framework.
retriever | prompt | model | parseris the canonical RAG pattern. Document loaders, splitters, and vector stores are all interchangeable components. - LangSmith is production observability. Enable tracing at startup. 89% of production teams use observability — without it, debugging agent behavior is guesswork.
- The ecosystem is the moat. 1000+ integrations mean model providers, vector stores, and tools are swappable with one line. Build against the interface, not the implementation.
Where to Start
| You already have... | Start here |
|---|---|
| Nothing — blank project | Install LangChain, build a basic LCEL chain |
| Documents to query | Build a RAG chain (load, split, embed, retrieve, generate) |
| A need for agentic behavior | Use create_agent with tools |
| Existing AgentExecutor code | Migrate to create_agent — see references/agent-patterns.md |
| A production deployment | Add LangSmith tracing + LangServe deployment |
| Comparing frameworks | See the Framework Routing Guide |
Pipeline Mode
| Mode | When | Phases to run | Skip |
|---|---|---|---|
| Quick | Single chain, exploration | prompt → model → parser | Retrieval, agents, production hardening |
| RAG | Document Q&A | load → split → embed → retrieve → generate | Agent orchestration, deployment |
| Agent | Tool-using agents | create_agent + tools + LangGraph runtime | If simple chain suffices |
| Production | Shipping to users | RAG/Agent + LangSmith + LangServe | Nothing |
Quick Reference
| Task | Approach | Reference | |||
|---|---|---|---|---|---|
| Basic chain | `prompt \ | model \ | parser` | references/lcel-reference.md | |
| RAG pipeline | `retriever \ | prompt \ | model \ | parser` | references/rag-strategies.md |
| Create agent | create_agent(model, tools, prompt) | references/agent-patterns.md | |||
| Tool definition | @tool decorator | references/agent-patterns.md | |||
| Multi-agent | LangGraph supervisor pattern | references/agent-patterns.md | |||
| Observability | Set LANGCHAINTRACINGV2=true | references/production-deployment.md | |||
| Deployment | LangServe or LangSmith Deployment | references/production-deployment.md | |||
| Vector store | One-line swap (Chroma, Pinecone, pgvector) | references/integration-ecosystem.md |
When to Use This Skill
Load this skill any time you are:
- Building LCEL chains for LLM-powered applications
- Implementing RAG pipelines over enterprise or personal data
- Creating agents with tool-calling and multi-step reasoning
- Deploying LLM applications to production with observability
- Comparing LangChain with LlamaIndex, Haystack, or raw API calls
Framework Routing Guide
This skill is part of a portfolio of framework skills. When deciding which fits:
| Scenario | Reach for | Why |
|---|---|---|
| I have chains to compose | LangChain | LCEL is the cleanest pipe-based composition model |
| I have documents to query | LlamaIndex | Data ingestion and retrieval are first-class primitives |
| I have agents to orchestrate | LangGraph | State-machine semantics, subgraphs, human-in-the-loop |
| I have a tool to wrap as an agent | PydanticAI | Type-safe agent definitions with dependency injection |
| I have search pipelines | Haystack | Pipeline model is more mature for search workloads |
| Fast prototype of any kind | LangChain | Fastest path from zero to working chain |
| A typed, bounded decision inside an agent workflow | System One | System One owns question/model behavior and calibration; use LangChain middleware or outer conditional orchestration as the implementation seam, and harness-engineering for placement and whole-task outcomes |
Reference Files
| Reference | Load when | File |
|---|---|---|
| LCEL Reference | Building chains with the pipe operator | references/lcel-reference.md |
| Architecture | Understanding package structure, Runnable, v1.0 | references/architecture.md |
| RAG Strategies | Building RAG pipelines | references/rag-strategies.md |
| Agent Patterns | Creating agents with tools and multi-agent | references/agent-patterns.md |
| Typed System One decision in an agent | Route the adapter seam, unknown lane, and handoff between model semantics and harness outcomes | references/agent-patterns.md — see “Keep typed decisions outside the chat model”; continue to harness-engineering for placement and whole-task evidence |
| Production & Deployment | LangServe, LangSmith, deployment | references/production-deployment.md |
| Integration Ecosystem | Model providers, vector stores, tools | references/integration-ecosystem.md |
| FAQ & Troubleshooting | Common errors and fixes | references/faq-and-troubleshooting.md |
| Callbacks System | Custom logging, monitoring, agent auditing | references/callbacks.md |
| Validation Audit | Research validation of all API claims | references/validation-audit.md |
Template Files
| Template | When to use | File |
|---|---|---|
| Basic Chain | Single prompt→model→parser chain | templates/basic-chain.py |
| RAG Pipeline | Document Q&A with retrieval | templates/rag-pipeline.py |
| Agent with Tools | Tool-using agent with LangGraph runtime | templates/agent-with-tools.py |
| Production Deploy | LangServe deployment with LangSmith | templates/production-deploy.py |
Scripts
| Script | Purpose | File |
|---|---|---|
| check-setup | Verify LangChain installation | scripts/check-setup.py |
Troubleshooting Guide
| Symptom | Likely cause | Fix | Reference |
|---|---|---|---|
| Chain returns nothing | Output parser not connected | Add .pipe(StrOutputParser()) or equivalent | references/lcel-reference.md |
| Agent not calling tools | Tool schema mismatch | Check tool has docstring and type hints | references/agent-patterns.md |
| LangSmith traces missing | LANGCHAINTRACINGV2 not set | Set env var before any chain execution | references/production-deployment.md |
| Deprecation warning | Using AgentExecutor | Migrate to create_agent (LangGraph runtime) | references/agent-patterns.md |
| Model not found | Integration package missing | Install langchain-openai, langchain-anthropic, etc. | references/integration-ecosystem.md |
| Streaming not working | LCEL chain not streaming-native | Ensure all components implement stream() | references/lcel-reference.md |
| Vector store connection fails | Wrong credentials or missing package | Install langchain-community + provider package | references/integration-ecosystem.md |
When NOT to Use LangChain
- Single-model, single-prompt application — raw API calls are simpler and more debuggable
- Maximum transparency needed — LangGraph (which LangChain uses underneath) provides more visibility
- Pure multi-agent state machines — LangGraph directly is the correct tool, not the high-level API
- Stateless microservice with no LLM orchestration — LangChain adds overhead without benefit
