Human-in-the-loop

The Human-in-the-Loop (HITL) middleware lets you add human oversight to agent tool calls. When a model proposes an action that might require review—for example, writing to a file or executing SQL—the middleware can pause execution and wait for a decision.

It does this by checking each tool call against a configurable policy. If intervention is needed, the middleware issues an interrupt that halts execution. The graph state is saved using LangGraph’s persistence layer, so execution can pause safely and resume later.

A human decision then determines what happens next: the action can be approved as-is (approve), modified before running (edit), rejected with feedback (reject), or responded to directly (respond) for “ask user” style tools.

Interrupt decision types

The middleware defines four built-in ways a human can respond to an interrupt:

Decision Type	Description	Example Use Case
✅ approve	Execute the tool with the original arguments as proposed by the agent.	Send an email draft exactly as written
✏️ edit	Modify the tool arguments before execution.	Change the recipient before sending an email
❌ reject	Skip executing this tool call entirely and return rejection feedback to the agent.	Deny file deletion and explain why
💬 respond	Return the human’s message directly as a synthetic tool result, skipping execution, for “ask user” style tools.	Answer an "ask_user" prompt with a direct reply

The available decision types for each tool depend on the policy you configure in interrupt_on. When multiple tool calls are paused at the same time, each action requires a separate decision. Decisions must be provided in the same order as the actions appear in the interrupt request.

Use reject when the human is denying the requested action. Use respond only when the human is acting as the tool, such as answering an ask_user prompt. Do not use respond to deny side-effecting tools, because its message is treated as a successful tool result.

When editing tool arguments, make changes conservatively. Significant modifications to the original arguments may cause the model to re-evaluate its approach and potentially execute the tool multiple times or take unexpected actions.

Configuring interrupts

To use HITL, add the middleware to the agent’s middleware list when creating the agent.

You configure it with a mapping of tool actions to the decision types that are allowed for each action. The middleware will interrupt execution when a tool call matches an action in the mapping.

import { createAgent, humanInTheLoopMiddleware } from "langchain";
import { MemorySaver } from "@langchain/langgraph";

const agent = createAgent({
    model: "gpt-5.5",
    tools: [writeFileTool, executeSQLTool, readDataTool],
    middleware: [
        humanInTheLoopMiddleware({
            interruptOn: {
                write_file: true, // All decisions (approve, edit, reject, respond) allowed
                execute_sql: {
                    allowedDecisions: ["approve", "reject"],
                    // No editing allowed
                    description: "🚨 SQL execution requires DBA approval",
                },
                // Safe operation, no approval needed
                read_data: false,
            },
            // Prefix for interrupt messages - combined with tool name and args to form the full message
            // e.g., "Tool execution pending approval: execute_sql with query='DELETE FROM...'"
            // Individual tools can override this by specifying a "description" in their interrupt config
            descriptionPrefix: "Tool execution pending approval",
        }),
    ],
    // Human-in-the-loop requires checkpointing to handle interrupts.
    // In production, use a persistent checkpointer like AsyncPostgresSaver or MongoDBSaver.
    checkpointer: new MemorySaver(),
});

You must configure a checkpointer to persist the graph state across interrupts.

In production, use a persistent checkpointer like AsyncPostgresSaver or MongoDBSaver. For testing or prototyping, use InMemorySaver.

When invoking the agent, pass a config that includes the thread ID to associate execution with a conversation thread. See the LangGraph interrupts documentation for details.

Configuration options

interruptOn · object · required

Mapping of tool names to approval configs

Tool approval config options:

allowAccept · boolean · default: "false"

Whether approval is allowed

allowEdit · boolean · default: "false"

Whether editing is allowed

allowRespond · boolean · default: "false"

Whether responding/rejection is allowed

Conditional interrupts

By default, every tool call listed in interrupt_on pauses for review. To pause only some calls, add a when predicate to a tool’s InterruptOnConfig. The predicate receives a ToolCallRequest and returns True to interrupt or False to auto-approve, so you can gate on the tool’s arguments.

Conditional interrupts are currently available in Python only.

Responding to interrupts

When you invoke the agent, it runs until it either completes or an interrupt is raised. An interrupt is triggered when a tool call matches the policy you configured in interrupt_on. With version="v2", the result is a GraphOutput with an interrupts attribute containing the actions that require review. You can then present those actions to a reviewer and resume execution once decisions are provided.

import { HumanMessage } from "@langchain/core/messages";
import { Command } from "@langchain/langgraph";

// You must provide a thread ID to associate the execution with a conversation thread,
// so the conversation can be paused and resumed (as is needed for human review).
const config = { configurable: { thread_id: "some_id" } };

// Run the graph until the interrupt is hit.
const result = await agent.invoke(
    {
        messages: [new HumanMessage("Delete old records from the database")],
    },
    config 
);


// The interrupt contains the full HITL request with action_requests and review_configs
console.log(result.__interrupt__);
// > [
// >    Interrupt(
// >       value: {
// >          actionRequests: [
// >             {
// >                name: 'execute_sql',
// >                arguments: { query: 'DELETE FROM records WHERE created_at < NOW() - INTERVAL \'30 days\';' },
// >                description: 'Tool execution pending approval\n\nTool: execute_sql\nArgs: {...}'
// >             }
// >          ],
// >          reviewConfigs: [
// >             {
// >                actionName: 'execute_sql',
// >                allowedDecisions: ['approve', 'reject']
// >             }
// >          ]
// >       }
// >    )
// > ]

// Resume with approval decision
await agent.invoke(
    new Command({
        resume: { decisions: [{ type: "approve" }] }, // or "reject"
    }),
    config // Same thread ID to resume the paused conversation
);

Decision types

✅ approve

Use approve to approve the tool call as-is and execute it without changes.

await agent.invoke(
    new Command({
        // Decisions are provided as a list, one per action under review.
        // The order of decisions must match the order of actions
        // in the interrupt request.
        resume: {
            decisions: [
                {
                    type: "approve",
                }
            ]
        }
    }),
    config  // Same thread ID to resume the paused conversation
);

✏️ edit

Use edit to modify the tool call before execution. Provide the edited action with the new tool name and arguments.

await agent.invoke(
    new Command({
        // Decisions are provided as a list, one per action under review.
        // The order of decisions must match the order of actions
        // in the interrupt request.
        resume: {
            decisions: [
                {
                    type: "edit",
                    // Edited action with tool name and args
                    editedAction: {
                        // Tool name to call.
                        // Will usually be the same as the original action.
                        name: "new_tool_name",
                        // Arguments to pass to the tool.
                        args: { key1: "new_value", key2: "original_value" },
                    }
                }
            ]
        }
    }),
    config  // Same thread ID to resume the paused conversation
);

When editing tool arguments, make changes conservatively. Significant modifications to the original arguments may cause the model to re-evaluate its approach and potentially execute the tool multiple times or take unexpected actions.

❌ reject

Use reject to deny the tool call and provide feedback instead of execution. The tool is not executed.

await agent.invoke(
    new Command({
        // Decisions are provided as a list, one per action under review.
        // The order of decisions must match the order of actions
        // in the interrupt request.
        resume: {
            decisions: [
                {
                    type: "reject",
                    // Optional: explain why the action was rejected
                    // and whether the agent should retry a different approach.
                    message: "User rejected this action. Do not retry this tool call.",
                }
            ]
        }
    }),
    config  // Same thread ID to resume the paused conversation
);

The message is added to the conversation as feedback to help the agent understand why the action was rejected and what it should do instead. When you omit message, the middleware uses a default rejection message that tells the model the tool was not executed and not to retry the same tool call unless the user asks. For side-effecting tools, provide a domain-specific message that is explicit about whether the agent should abandon the action, ask a follow-up question, or try a safer alternative.

💬 respond

Use respond for “ask user” style tools where the tool’s real implementation is the human’s reply. The message content is returned directly as the tool result; the tool itself is not executed.

await agent.invoke(
    new Command({
        // Decisions are provided as a list, one per action under review.
        // The order of decisions must match the order of actions
        // in the interrupt request.
        resume: {
            decisions: [
                {
                    type: "respond",
                    // The human's reply, returned directly as the tool result
                    message: "Blue.",
                }
            ]
        }
    }),
    config  // Same thread ID to resume the paused conversation
);

The message is returned to the agent as a successful ToolMessage. Use respond when the tool is intentionally a placeholder for human input, for example, an ask_user tool that prompts for clarification. Do not use respond to deny a proposed action, because it tells the model that the tool completed successfully.

---

Multiple decisions

When multiple actions are under review, provide a decision for each action in the same order as they appear in the interrupt:

{
    decisions: [
        { type: "approve" },
        {
            type: "edit",
            editedAction: {
                name: "tool_name",
                args: { param: "new_value" }
            }
        },
        {
            type: "reject",
            message: "This action is not allowed"
        }
    ]
}

Streaming with human-in-the-loop

You can stream real-time updates while the agent runs and handles interrupts using stream_events(). Use stream.messages to stream LLM tokens and stream.values to check agent state snapshots for interrupts.

import { Command } from "@langchain/langgraph";

const config = { configurable: { thread_id: "some_id" } };

// Stream agent progress and LLM tokens until interrupt
const stream = await agent.streamEvents(
    { messages: [{ role: "user", content: "Delete old records from the database" }] },
    { ...config, version: "v3" }
);
for await (const message of stream.messages) {
    for await (const token of message.text) {
        process.stdout.write(token);
    }
}

// Check whether the run paused for human input
if (stream.interrupted) {
    console.log(`\n\nInterrupt: ${JSON.stringify(stream.interrupts)}`);
}

// Resume with streaming after human decision
const resumeStream = await agent.streamEvents(
    new Command({ resume: { decisions: [{ type: "approve" }] } }),
    { ...config, version: "v3" }
);
for await (const message of resumeStream.messages) {
    for await (const token of message.text) {
        process.stdout.write(token);
    }
}

See the Streaming guide for more details on stream modes.

Execution lifecycle

The middleware defines an after_model hook that runs after the model generates a response but before any tool calls are executed:

1. The agent invokes the model to generate a response.
2. The middleware inspects the response for tool calls.
3. If any calls require human input, the middleware builds a HITLRequest with action_requests and review_configs and calls interrupt.
4. The agent waits for human decisions.
5. Based on the HITLResponse decisions, the middleware executes approved or edited calls, synthesizes ToolMessage’s for rejected calls, returns human replies directly as ToolMessage’s for respond decisions, and resumes execution.

Custom HITL logic

For more specialized workflows, you can build custom HITL logic directly using the interrupt primitive and middleware abstraction.

Review the execution lifecycle above to understand how to integrate interrupts into the agent’s operation.

---

Connect these docs to Claude, VSCode, and more via MCP for real-time answers.

Edit this page on GitHub or file an issue.