langgraph-human-in-the-loop

</python>
<typescript>
Pause execution for human review and resume with Command.
```typescript
import { interrupt, Command, MemorySaver, StateGraph, StateSchema, START, END } from "@langchain/langgraph";
import { z } from "zod";
 
const State = new StateSchema({
  approved: z.boolean().default(false),
});
 
const approvalNode = async (state: typeof State.State) => {
  // Pause and ask for approval
  const approved = interrupt("Do you approve this action?");
  // When resumed, Command({ resume }) returns that value here
  return { approved };
};
 
const checkpointer = new MemorySaver();
const graph = new StateGraph(State)
  .addNode("approval", approvalNode)
  .addEdge(START, "approval")
  .addEdge("approval", END)
  .compile({ checkpointer });
 
const config = { configurable: { thread_id: "thread-1" } };
 
// Initial run — hits interrupt and pauses
let result = await graph.invoke({ approved: false }, config);
console.log(result.__interrupt__);
// [{ value: 'Do you approve this action?', ... }]
 
// Resume with the human's response
result = await graph.invoke(new Command({ resume: true }), config);
console.log(result.approved);  // true

# interrupt() must come first — any code before it will re-run on resume
human_decision = interrupt({
    "email_id": state.get("email_content", ""),
    "draft_response": state.get("draft_response", ""),
    "urgency": classification.get("urgency"),
    "action": "Please review and approve/edit this response"
})
 
# Process the human's decision
if human_decision.get("approved"):
    return Command(
        update={"draft_response": human_decision.get("edited_response", state.get("draft_response", ""))},
        goto="send_reply"
    )
else:
    # Rejection — human will handle directly
    return Command(update={}, goto=END)

</python>
<typescript>
Interrupt for human review, then route to send or end based on the decision.
```typescript
import { interrupt, Command, END, GraphNode } from "@langchain/langgraph";
 
const humanReview: GraphNode<typeof EmailAgentState> = async (state) => {
  const classification = state.classification!;
 
  // interrupt() must come first — any code before it will re-run on resume
  const humanDecision = interrupt({
    emailId: state.emailContent,
    draftResponse: state.responseText,
    urgency: classification.urgency,
    action: "Please review and approve/edit this response",
  });
 
  // Process the human's decision
  if (humanDecision.approved) {
    return new Command({
      update: { responseText: humanDecision.editedResponse || state.responseText },
      goto: "sendReply",
    });
  } else {
    return new Command({ update: {}, goto: END });
  }
};

while True:
    answer = interrupt(prompt)
 
    # Validate the input
    if isinstance(answer, int) and answer > 0:
        break
    else:
        # Invalid input — ask again with a more specific prompt
        prompt = f"'{answer}' is not a valid age. Please enter a positive number."
 
return {"age": answer}

 
Each `Command(resume=...)` call provides the next answer. If invalid, the loop re-interrupts with a clearer message.
```python
config = {"configurable": {"thread_id": "form-1"}}
first = graph.invoke({"age": None}, config)
# __interrupt__: "What is your age?"
 
retry = graph.invoke(Command(resume="thirty"), config)
# __interrupt__: "'thirty' is not a valid age..."
 
final = graph.invoke(Command(resume=30), config)
print(final["age"])  # 30

// Validate the input
if (typeof answer === "number" && answer > 0) {
  return { age: answer };
} else {
  // Invalid input — ask again with a more specific prompt
  prompt = `'${answer}' is not a valid age. Please enter a positive number.`;
}

</typescript>
</ex-validation-loop>
 
---
 
## Multiple Interrupts
 
When parallel branches each call `interrupt()`, resume all of them in a single invocation by mapping each interrupt ID to its resume value.
 
<ex-multiple-interrupts>
<python>
Resume multiple parallel interrupts by mapping interrupt IDs to values.
```python
from typing import Annotated, TypedDict
import operator
from langgraph.checkpoint.memory import InMemorySaver
from langgraph.graph import START, END, StateGraph
from langgraph.types import Command, interrupt
 
class State(TypedDict):
    vals: Annotated[list[str], operator.add]
 
def node_a(state):
    answer = interrupt("question_a")
    return {"vals": [f"a:{answer}"]}
 
def node_b(state):
    answer = interrupt("question_b")
    return {"vals": [f"b:{answer}"]}
 
graph = (
    StateGraph(State)
    .add_node("a", node_a)
    .add_node("b", node_b)
    .add_edge(START, "a")
    .add_edge(START, "b")
    .add_edge("a", END)
    .add_edge("b", END)
    .compile(checkpointer=InMemorySaver())
)
 
config = {"configurable": {"thread_id": "1"}}
 
# Both parallel nodes hit interrupt() and pause
result = graph.invoke({"vals": []}, config)
# result["__interrupt__"] contains both Interrupt objects with IDs
 
# Resume all pending interrupts at once using a map of id -> value
resume_map = {
    i.id: f"answer for {i.value}"
    for i in result["__interrupt__"]
}
result = graph.invoke(Command(resume=resume_map), config)
# result["vals"] = ["a:answer for question_a", "b:answer for question_b"]

</typescript>
</ex-multiple-interrupts>
 
User-fixable errors use `interrupt()` to pause and collect missing data — that's the pattern covered by this skill. For the full 4-tier error handling strategy (RetryPolicy, Command error loops, etc.), see the **fundamentals** skill.
 
---
 
## Side Effects Before Interrupt Must Be Idempotent
 
When the graph resumes, the node restarts from the **beginning** — ALL code before `interrupt()` re-runs. In subgraphs, BOTH the parent node and the subgraph node re-execute.
 
<idempotency-rules>
 
**Do:**
- Use **upsert** (not insert) operations before `interrupt()`
- Use **check-before-create** patterns
- Place side effects **after** `interrupt()` when possible
- Separate side effects into their own nodes
 
**Don't:**
- Create new records before `interrupt()` — duplicates on each resume
- Append to lists before `interrupt()` — duplicate entries on each resume
 
</idempotency-rules>
 
<ex-idempotent-patterns>
<python>
Idempotent operations before interrupt vs non-idempotent (wrong).
```python
# GOOD: Upsert is idempotent — safe before interrupt
def node_a(state: State):
    db.upsert_user(user_id=state["user_id"], status="pending_approval")
    approved = interrupt("Approve this change?")
    return {"approved": approved}
 
# GOOD: Side effect AFTER interrupt — only runs once
def node_a(state: State):
    approved = interrupt("Approve this change?")
    if approved:
        db.create_audit_log(user_id=state["user_id"], action="approved")
    return {"approved": approved}
 
# BAD: Insert creates duplicates on each resume!
def node_a(state: State):
    audit_id = db.create_audit_log({  # Runs again on resume!
        "user_id": state["user_id"],
        "action": "pending_approval",
    })
    approved = interrupt("Approve this change?")
    return {"approved": approved}

</typescript>
</ex-idempotent-patterns>
 
<subgraph-interrupt-re-execution>
 
### Subgraph re-execution on resume
 
When a subgraph contains an `interrupt()`, resuming re-executes BOTH the parent node (that invoked the subgraph) AND the subgraph node (that called `interrupt()`):
 
<python>
```python
def node_in_parent_graph(state: State):
    some_code()  # <-- Re-executes on resume
    subgraph_result = subgraph.invoke(some_input)
    # ...
 
def node_in_subgraph(state: State):
    some_other_code()  # <-- Also re-executes on resume
    result = interrupt("What's your name?")
    # ...

</typescript>
</subgraph-interrupt-re-execution>
 
---
 
## Command(resume) Warning
 
`Command(resume=...)` is the **only** Command pattern intended as input to `invoke()`/`stream()`. Do NOT pass `Command(update=...)` as input — it resumes from the latest checkpoint and the graph appears stuck. See the fundamentals skill for the full antipattern explanation.
 
---
 
## Fixes
 
<fix-checkpointer-required-for-interrupts>
<python>
Checkpointer required for interrupt functionality.
```python
# WRONG
graph = builder.compile()
 
# CORRECT
graph = builder.compile(checkpointer=InMemorySaver())

</typescript>
</fix-checkpointer-required-for-interrupts>
 
<fix-resume-with-command>
<python>
Use Command to resume from an interrupt (regular dict restarts graph).
```python
# WRONG
graph.invoke({"resume_data": "approve"}, config)
 
# CORRECT
graph.invoke(Command(resume="approve"), config)

</typescript>
</fix-resume-with-command>
 
<boundaries>
### What You Should NOT Do
 
- Use interrupts without a checkpointer — will fail
- Resume without the same thread_id — creates a new thread instead of resuming
- Pass `Command(update=...)` as invoke input — graph appears stuck (use plain dict)
- Perform non-idempotent side effects before `interrupt()` — creates duplicates on resume
- Assume code before `interrupt()` only runs once — it re-runs every resume
</boundaries>