Agent skill

langchain-ecosystem

Complete guide for LangChain, LangGraph, and Deep Agents development. Covers framework selection, agents, tools, RAG, middleware, graphs, persistence, HITL, subagents, and memory. Triggers when code imports langchain/langgraph/deepagents, or user asks about building AI agents, RAG pipelines, stateful graphs, human-in-the-loop workflows, or agent orchestration.

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npx add-skill https://github.com/JoaquinCampo/Skills/tree/main/langchain-ecosystem

SKILL.md

LangChain Ecosystem Router

Framework Selection

Frameworks are layered, not competing:

┌─────────────────────────────────────┐
│         Deep Agents                 │  ← planning, memory, skills, files
├─────────────────────────────────────┤
│          LangGraph                  │  ← graphs, loops, state, control flow
├─────────────────────────────────────┤
│         LangChain                   │  ← models, tools, prompts, RAG
└─────────────────────────────────────┘

Decision tree (answer in order):

  1. Needs sub-tasks, file management, persistent memory, or on-demand skills? → Deep Agents
  2. Needs complex control flow (loops, branching, parallel, human-in-the-loop)? → LangGraph
  3. Single-purpose agent with fixed tools? → LangChain (create_agent)
  4. Pure model call, chain, or retrieval pipeline? → LangChain (LCEL)
Capability LangChain LangGraph Deep Agents
Control flow Fixed tool loop Custom graph Middleware-managed
Planning ✗ Manual ✓ TodoListMiddleware
File management ✗ Manual ✓ FilesystemMiddleware
Persistent memory ✗ With checkpointer ✓ MemoryMiddleware
Subagent delegation ✗ Manual ✓ SubAgentMiddleware
Human-in-the-loop ✗ Manual interrupt ✓ HumanInTheLoopMiddleware

LangChain tools/chains/retrievers work inside LangGraph nodes and Deep Agents tools. LangGraph compiled graphs can be registered as Deep Agents subagents.

Quick Start (Most Common Patterns)

Simple agent:

python
from langchain.agents import create_agent
agent = create_agent(model="anthropic:claude-sonnet-4-5", tools=[my_tool])
result = agent.invoke({"messages": [{"role": "user", "content": "Hello"}]})
print(result["messages"][-1].content)

Stateful graph:

python
from langgraph.graph import StateGraph, START, END
graph = StateGraph(State).add_node("process", fn).add_edge(START, "process").add_edge("process", END).compile()

Deep Agent:

python
from deepagents import create_deep_agent
agent = create_deep_agent(model="claude-sonnet-4-5-20250929", tools=[my_tool], system_prompt="...")

Critical Rules (All Frameworks)

  • Persistence always needs thread_id: config = {"configurable": {"thread_id": "..."}}
  • HITL always needs checkpointer: MemorySaver() at minimum
  • Resume after interrupt: Command(resume={"decisions": [{"type": "approve"}]}) — never plain dict
  • LangChain 1.0 is LTS — never start new projects on 0.3
  • Always install langchain-core explicitly — not auto-hoisted in monorepos
  • Use dedicated packages (e.g., langchain-chroma) not langchain_community

Deep-Dive References

LangChain

Reference When to Read
references/langchain-fundamentals.md create_agent, tool definitions, persistence, TypeScript
references/langchain-dependencies.md Package versions, install commands, import paths, environment setup
references/langchain-middleware.md HumanInTheLoopMiddleware, approval/edit/reject, per-tool policies
references/langchain-rag.md Document loaders, splitters, embeddings, vector stores, MMR search

LangGraph

Reference When to Read
references/langgraph-fundamentals.md StateGraph, reducers, nodes, edges, Command, Send, streaming
references/langgraph-human-in-the-loop.md interrupt(), idempotency, approval workflows, parallel interrupts
references/langgraph-persistence.md Checkpointers, Store, time travel, subgraph scoping

Deep Agents

Reference When to Read
references/deep-agents-core.md create_deep_agent, built-in tools, SKILL.md format, configuration
references/deep-agents-memory.md StateBackend, StoreBackend, FilesystemBackend, CompositeBackend
references/deep-agents-orchestration.md Subagents, task delegation, TodoList, HITL approval flow

Meta

Reference When to Read
references/framework-selection.md Full decision tree, capability matrix, interoperability details

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