How to add static breakpoints¶

Prerequisites

This guide assumes familiarity with the following concepts:

Human-in-the-loop (HIL) interactions are crucial for agentic systems. Breakpoints are a common HIL interaction pattern, allowing the graph to stop at specific steps and seek human approval before proceeding (e.g., for sensitive actions).

Breakpoints are built on top of LangGraph checkpoints, which save the graph's state after each node execution. Checkpoints are saved in threads that preserve graph state and can be accessed after a graph has finished execution. This allows for graph execution to pause at specific points, await human approval, and then resume execution from the last checkpoint.

Setup¶

Code for your graph¶

In this how-to we use a simple ReAct style hosted graph (you can see the full code for defining it here). The important thing is that there are two nodes (one named agent that calls the LLM, and one named action that calls the tool), and a routing function from agent that determines whether to call action next or just end the graph run (the action node always calls the agent node after execution).

SDK Initialization¶

PythonJavascriptCURL

from langgraph_sdk import get_client
client = get_client(url=<DEPLOYMENT_URL>)
# Using the graph deployed with the name "agent"
assistant_id = "agent"
thread = await client.threads.create()

import { Client } from "@langchain/langgraph-sdk";

const client = new Client({ apiUrl: <DEPLOYMENT_URL> });
// Using the graph deployed with the name "agent"
const assistantId = "agent";
const thread = await client.threads.create();

curl --request POST \
  --url <DEPLOYMENT_URL>/threads \
  --header 'Content-Type: application/json' \
  --data '{}'

Adding a breakpoint¶

We now want to add a breakpoint in our graph run, which we will do before a tool is called. We can do this by adding interrupt_before=["action"], which tells us to interrupt before calling the action node. We can do this either when compiling the graph or when kicking off a run. Here we will do it when kicking of a run, if you would like to to do it at compile time you need to edit the python file where your graph is defined and add the interrupt_before parameter when you call .compile.

First let's access our hosted LangGraph instance through the SDK:

And, now let's compile it with a breakpoint before the tool node:

PythonJavascriptCURL

input = {"messages": [{"role": "user", "content": "what's the weather in sf"}]}
async for chunk in client.runs.stream(
    thread["thread_id"],
    assistant_id,
    input=input,
    stream_mode="updates",
    interrupt_before=["action"],
):
    print(f"Receiving new event of type: {chunk.event}...")
    print(chunk.data)
    print("\n\n")

const input = { messages: [{ role: "human", content: "what's the weather in sf" }] };

const streamResponse = client.runs.stream(
  thread["thread_id"],
  assistantId,
  {
    input: input,
    streamMode: "updates",
    interruptBefore: ["action"]
  }
);

for await (const chunk of streamResponse) {
  console.log(`Receiving new event of type: ${chunk.event}...`);
  console.log(chunk.data);
  console.log("\n\n");
}

curl --request POST \
 --url <DEPLOYMENT_URL>/threads/<THREAD_ID>/runs/stream \
 --header 'Content-Type: application/json' \
 --data "{
   \"assistant_id\": \"agent\",
   \"input\": {\"messages\": [{\"role\": \"human\", \"content\": \"what's the weather in sf\"}]},
   \"interrupt_before\": [\"action\"],
   \"stream_mode\": [
     \"messages\"
   ]
 }" | \
 sed 's/\r$//' | \
 awk '
 /^event:/ {
     if (data_content != "") {
         print data_content "\n"
     }
     sub(/^event: /, "Receiving event of type: ", $0)
     printf "%s...\n", $0
     data_content = ""
 }
 /^data:/ {
     sub(/^data: /, "", $0)
     data_content = $0
 }
 END {
     if (data_content != "") {
         print data_content "\n"
     }
 }
 '

Output:

Receiving new event of type: metadata...
{'run_id': '3b77ef83-687a-4840-8858-0371f91a92c3'}



Receiving new event of type: data...
{'agent': {'messages': [{'content': [{'id': 'toolu_01HwZqM1ptX6E15A5LAmyZTB', 'input': {'query': 'weather in san francisco'}, 'name': 'tavily_search_results_json', 'type': 'tool_use'}], 'additional_kwargs': {}, 'response_metadata': {}, 'type': 'ai', 'name': None, 'id': 'run-e5d17791-4d37-4ad2-815f-a0c4cba62585', 'example': False, 'tool_calls': [{'name': 'tavily_search_results_json', 'args': {'query': 'weather in san francisco'}, 'id': 'toolu_01HwZqM1ptX6E15A5LAmyZTB'}], 'invalid_tool_calls': []}]}}



Receiving new event of type: end...
None