langgraph-human-in-the-loop

name	langgraph-human-in-the-loop
description	INVOKE THIS SKILL when implementing human-in-the-loop patterns, pausing for approval, or handling errors in LangGraph. Covers interrupt(), Command(resume=...), approval/validation workflows, and the 4-tier error handling strategy.

LangGraph's human-in-the-loop patterns let you pause graph execution, surface data to users, and resume with their input:

• interrupt(value) — pauses execution, surfaces a value to the caller
• Command(resume=value) — resumes execution, providing the value back to interrupt()
• Checkpointer — required to save state while paused
• Thread ID — required to identify which paused execution to resume

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Requirements

Three things are required for interrupts to work:

1. Checkpointer — compile with checkpointer=InMemorySaver() (dev) or PostgresSaver (prod)
2. Thread ID — pass {"configurable": {"thread_id": "..."}} to every invoke/stream call
3. JSON-serializable payload — the value passed to interrupt() must be JSON-serializable

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Basic Interrupt + Resume

interrupt(value) pauses the graph. The value surfaces in the result under __interrupt__. Command(resume=value) resumes — the resume value becomes the return value of interrupt().

Critical: when the graph resumes, the node restarts from the beginning — all code before interrupt() re-runs.

Pause execution for human review and resume with Command. ```python from langgraph.types import interrupt, Command from langgraph.checkpoint.memory import InMemorySaver from langgraph.graph import StateGraph, START, END from typing_extensions import TypedDict Interrupt for human review, then route to send or end based on the decision. ```python from langgraph.types import interrupt, Command from langgraph.graph import StateGraph, START, END from typing import Literal from typing_extensions import TypedDict Validate human input in a loop, re-prompting until valid. ```python from langgraph.types import interrupt Validate human input in a loop, re-prompting until valid. ```typescript import { interrupt } from "@langchain/langgraph"; Resume multiple parallel interrupts by mapping interrupt IDs to values. ```typescript import { Command, END, MemorySaver, START, StateGraph, interrupt, isInterrupted, INTERRUPT, Annotation } from "@langchain/langgraph"; Idempotent operations before interrupt vs non-idempotent (wrong). ```typescript // GOOD: Upsert is idempotent — safe before interrupt const nodeA = async (state: typeof State.State) => { await db.upsertUser({ userId: state.userId, status: "pending_approval" }); const approved = interrupt("Approve this change?"); return { approved }; }; ```typescript async function nodeInParentGraph(state: State) { someCode(); // <-- Re-executes on resume const subgraphResult = await subgraph.invoke(someInput); // ... } Checkpointer required for interrupt functionality. ```typescript // WRONG const graph = builder.compile(); Use Command to resume from an interrupt (regular object restarts graph). ```typescript // WRONG await graph.invoke({ resumeData: "approve" }, config);