How to Fix 'chain execution stuck during development' in AutoGen (TypeScript)

When AutoGen says the chain execution is stuck during development, it usually means one agent or tool call never resolves, so the next step in the chain never runs. In TypeScript, this most often shows up when you wire a UserProxyAgent, AssistantAgent, or custom tool with an async handler that doesn’t return, never terminates, or waits on input that never arrives.

The symptom is usually obvious: the process keeps running, no new messages are produced, and you may see logs like chain execution stuck during development, awaiting next response, or a conversation that stops after the first turn.

The Most Common Cause

The #1 cause is a tool or message handler that returns a promise which never resolves. In AutoGen TypeScript, this usually happens when you register an async function and forget to return a value, or you wait on stdin / external I/O inside a flow that expects deterministic completion.

Here’s the broken pattern versus the fixed one:

// BROKEN: hangs because the promise never resolves
import { AssistantAgent, UserProxyAgent } from "@autogen/agent";

const assistant = new AssistantAgent({
  name: "assistant",
  modelClient,
});

const userProxy = new UserProxyAgent({
  name: "user",
  modelClient,
});

userProxy.registerTool(
  "getPolicyStatus",
  async ({ policyId }: { policyId: string }) => {
    console.log(`Checking policy ${policyId}`);

    // Bug: this function never returns anything.
    // If you await something that never settles, the chain stalls.
    await new Promise(() => {});
  }
);

// FIXED: always resolve and return a serializable result
import { AssistantAgent, UserProxyAgent } from "@autogen/agent";

const assistant = new AssistantAgent({
  name: "assistant",
  modelClient,
});

const userProxy = new UserProxyAgent({
  name: "user",
  modelClient,
});

userProxy.registerTool(
  "getPolicyStatus",
  async ({ policyId }: { policyId: string }) => {
    console.log(`Checking policy ${policyId}`);

    const status = await fetchPolicyStatus(policyId);

    return {
      policyId,
      status,
      checkedAt: new Date().toISOString(),
    };
  }
);

A second version of this bug is forgetting to terminate the conversation loop. If you use GroupChatManager or a custom orchestration loop, make sure there is an exit condition.

// BROKEN: no stop condition
while (true) {
  await manager.run();
}

// FIXED: stop when done
for (let i = 0; i < 10; i++) {
  const result = await manager.run();
  if (result.isDone) break;
}

Other Possible Causes

1. The agent is waiting for human input that never comes

If you use UserProxyAgent with human-in-the-loop mode enabled, AutoGen may pause waiting for input.

const userProxy = new UserProxyAgent({
  name: "user",
  humanInputMode: "ALWAYS", // can block execution
});

Fix it by switching to automatic mode for development runs:

const userProxy = new UserProxyAgent({
  name: "user",
  humanInputMode: "NEVER",
});

2. Your tool returns non-serializable data

AutoGen message passing expects JSON-safe content. Returning a class instance, circular object, or raw stream can stall serialization and make debugging painful.

// BROKEN
return {
  customer: new Customer("123"),
};

// FIXED
return {
  customer: {
    id: "123",
    tier: "gold",
  },
};

3. The model call is hanging due to bad client config

A wrong endpoint, missing API key, or zero timeout can look like a stuck chain.

const modelClient = new OpenAIChatCompletionClient({
  model: "gpt-4o-mini",
  apiKey: process.env.OPENAI_API_KEY,
  timeoutMs: undefined, // risky in dev
});

Use an explicit timeout and verify connectivity:

const modelClient = new OpenAIChatCompletionClient({
  model: "gpt-4o-mini",
  apiKey: process.env.OPENAI_API_KEY!,
  timeoutMs: 30000,
});

4. Recursive agent calls without a termination guard

If an assistant keeps calling itself through tools or nested chats, you can create an infinite loop.

// BROKEN conceptually:
// assistant -> tool -> assistant -> tool -> ...

Add guards like max turns or recursion depth:

const manager = new GroupChatManager({
  maxTurns: 8,
});

How to Debug It

1. •

   Check whether the last log line is from a tool

   • •If you see something like Executing tool getPolicyStatus... and nothing after it, your tool handler is probably hanging.
   • •Add logs before and after every awaited call inside the handler.
2. •

   Disable human input

   • •Set humanInputMode: "NEVER" on UserProxyAgent.
   • •If the issue disappears, your chain was blocked waiting for interactive input.
3. •

   Return hardcoded values from tools

   • •Replace real API calls with a simple static object.
   • •If the chain starts working again, the problem is in your downstream I/O or serialization path.
4. •

   Add timeouts around external calls

   • •Wrap HTTP/database work so you fail fast instead of hanging forever.
   • •A dead socket should produce an error like Request timed out, not an infinite wait.

Prevention

• •

  Keep tool handlers pure and fast.

• •

  Always return JSON-serializable objects from tools.

• •

  Set explicit limits:

  • •maxTurns
  • •request timeouts
  • •recursion guards
• •

  During development:

  • •use humanInputMode: "NEVER"
  • •mock external APIs
  • •log every agent/tool boundary

If your AutoGen TypeScript chain is stuck during development, start with the tool layer first. In practice, that’s where most “nothing happens” bugs live.

Keep learning

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By Cyprian Aarons, AI Consultant at Topiax.