| name | langchain |
| description | Build and refactor LangChain/LangGraph agent systems with reliable tool calling, state design, and prompt boundaries. Use for tasks involving chains, ReAct agents, LangGraph nodes/edges, memory, and model/tool orchestration. |
LangChain Skill
Use this skill when implementing or reviewing LangChain/LangGraph flows.
When to apply
- Adding or modifying LangGraph nodes, edges, or state
- Implementing ReAct agents and tool lists
- Improving prompt boundaries and output parsing
- Debugging agent/tool failures and non-deterministic behavior
- Adding streaming behavior or thread continuity
Workflow
- Map the runtime path first.
- Identify entrypoint and the exact execution path.
- List state keys consumed/produced per node.
- Make state explicit and typed.
- Keep a single typed state object per graph.
- Add defaults/fallbacks for optional values.
- Keep tool surfaces narrow.
- Prefer small, composable tools.
- Write tool docstrings for invocation intent.
- Return machine-parsable outputs when possible.
- Enforce output contracts.
- Use strict JSON response instructions for structured steps.
- Add graceful fallback parsing behavior.
- Separate responsibilities.
- Retrieval/extraction/storage/synthesis should be different steps.
- Avoid hidden side effects in prompt-only logic.
- Instrument for observability.
- Add
@traceable on node-level and key tool wrappers.
- Verify traces include tool sequence and node timings.
Patterns to prefer
- Deterministic graph topology with explicit handoffs
- ReAct for tool selection; direct chain calls for strict transforms
- Thread IDs passed through API boundary and normalized server-side
- Model/provider split by task type (extraction vs synthesis vs chat)
Anti-patterns
- A monolithic prompt doing extraction + retrieval + synthesis
- Implicit state writes without schema updates
- Broad tools with hidden branching side effects
- Missing error handling for tool/model output parsing
Validation checklist
- Graph compiles and node transitions are valid
- Each node reads only required state keys
- Structured outputs parse successfully under malformed responses
- Tool calls and model outputs appear correctly in traces
