LangChain Agents Workflow

This skill is the entry point — read it first, then load the more specific skill for the step you're on.

Version floors this bundle assumes

• langchain >= 1.2 (v1 series — middleware-first create_agent)
• langgraph >= 1.1, langgraph-cli >= 0.4
• deepagents >= 0.5.3 (async sub-agents, structured sub-agent responses, filesystem permissions; model=None deprecated)
• langsmith >= 0.7 (pytest plugin + new evaluator API)
• langchain-anthropic >= 1.4, langchain-openai >= 1.0

If a project pins anything below these floors, suggest the bump before writing code — the API shapes in this bundle assume the v1+ surface.

You have two complementary tools

This skill bundle pairs with the mcpdoc MCP server. The two have distinct roles; use both.

Rule of thumb: when you need an exact API detail, fetch from mcpdoc. When you need to make a design decision, load a skill. When in doubt, do both.

When to load which skill

Mental model

Three layers in the modern stack:

1. create_agent(model, tools, middleware=...) — the v1 default for building agents. Middleware is how you add retries, fallbacks, summarization, HITL, PII handling, call limits. Read the middleware skill for the production stack.
2. Raw LangGraph (StateGraph) — drop down when create_agent isn't enough (multi-graph workflows, custom state, parallel branches). Read langgraph-code.
3. DeepAgents — create_deep_agent(...) is create_agent(...) pre-loaded with FilesystemMiddleware + SubAgentMiddleware + TodoListMiddleware. Read deepagents-code.

For non-agentic flows (RAG, classification), use plain LCEL chains — middleware does not apply to chains.

Common commands by lifecycle stage

Hard rules

• Look up exact APIs via mcpdoc, don't guess. If mcpdoc isn't configured, ask the user to set it up (see this repo's README) before you write LangChain code.
• Always check what's already installed before suggesting pip install — pip show langchain langgraph deepagents langsmith.
• Never print .env contents — refer to keys by name only.
• For ANY production agent, add the production middleware stack (call limits, retries, fallback, summarization). Copy-paste-ready in the middleware skill.
• Run smoke evals before any deploy. Not enforced — you must do it.
• Read the project structure first (ls, tree -L 2) before assuming layout.

Required environment variables (most projects)

• LANGSMITH_API_KEY — for tracing and evals.
• LANGSMITH_TRACING=true — enables trace capture.
• LANGSMITH_PROJECT — trace bucket name.
• One of OPENAI_API_KEY, ANTHROPIC_API_KEY, etc.

If any are missing when needed, fail fast with a clear message that names the missing variable.

Source: cwijayasundara/agent_cli_langchain — distributed by TomeVault.