How to Fix 'prompt template error in production' in AutoGen (TypeScript)

When AutoGen throws a prompt template error in production, it usually means the agent tried to render a template with missing or mismatched variables. In TypeScript, this shows up most often when you pass the wrong shape into an agent, tool, or chat message and the prompt renderer can’t resolve placeholders like {input} or {task}.

This is not a model issue. It’s almost always a template/data contract problem between your code and AutoGen’s prompt construction.

The Most Common Cause

The #1 cause is passing a payload that does not match the template variables expected by the agent or prompt builder.

In AutoGen TypeScript, this often happens when you define a prompt with placeholders but call the agent with a different key name, or you pass raw strings where an object is expected.

// BROKEN
import { AssistantAgent } from "@autogen/agent";

const agent = new AssistantAgent({
  name: "support_agent",
  systemMessage: "You are a helpful assistant.",
  // Somewhere inside your app you use a template like:
  // "Resolve this task: {task}"
});

await agent.run({
  input: "Check policy status for customer 123", // wrong key
});

// FIXED
import { AssistantAgent } from "@autogen/agent";

const agent = new AssistantAgent({
  name: "support_agent",
  systemMessage: "You are a helpful assistant.",
});

await agent.run({
  task: "Check policy status for customer 123", // matches template variable
});

If you see errors like:

• •Error: Missing value for prompt variable 'task'
• •Error: Failed to render prompt template
• •AutoGenError: prompt template error

then your first check is the variable contract between the caller and the template.

Other Possible Causes

1. Message content is not a string

Some AutoGen message types expect content to be a string. If you pass an object directly, template rendering can fail downstream.

// BROKEN
await agent.send({
  role: "user",
  content: { text: "Summarize this claim" }, // object instead of string
});

// FIXED
await agent.send({
  role: "user",
  content: "Summarize this claim",
});

2. Undefined values in interpolated strings

If you build prompts manually and interpolate undefined, AutoGen may surface a template failure later in execution.

// BROKEN
const policyId = undefined;
const prompt = `Review policy ${policyId} and summarize issues`;

// FIXED
const policyId = getPolicyId();
if (!policyId) throw new Error("policyId is required");

const prompt = `Review policy ${policyId} and summarize issues`;

3. Tool schema does not match function arguments

If you register tools with one schema and call them with another, AutoGen will fail while constructing or validating tool prompts.

// BROKEN
const tools = [{
  name: "lookupCustomer",
  description: "Lookup customer by id",
  parameters: {
    type: "object",
    properties: {
      customer_id: { type: "string" },
    },
    required: ["customer_id"],
  },
}];

// later...
await agent.run({
  customerId: "123", // mismatch with customer_id
});

// FIXED
await agent.run({
  customer_id: "123",
});

4. Wrong model/client configuration

A misconfigured model client can produce misleading prompt errors if the request never reaches the model cleanly.

// BROKEN
const client = new OpenAIChatCompletionClient({
  model: "", // empty model name
});

// FIXED
const client = new OpenAIChatCompletionClient({
  model: "gpt-4o-mini",
});

Also verify environment variables:

OPENAI_API_KEY=your_key_here

If the client cannot initialize properly, AutoGen may fail before it even gets to generation.

How to Debug It

1. •

   Inspect the exact missing variable

   • •Look for messages like Missing value for prompt variable 'task'.
   • •That tells you which placeholder failed during rendering.
2. •

   Log the final payload before calling AutoGen

   • •Print the object you pass into agent.run(), send(), or your custom wrapper.
   • •Check for typos like input vs task, customerId vs customer_id.
3. •

   Search for all template placeholders

   • •Grep your codebase for {...} patterns in prompts.
   • •Make sure every placeholder has a matching runtime value.
4. •

   Validate tool/message schemas

   • •Confirm that tool parameter names match exactly.
   • •Confirm that message content is plain text unless the API explicitly supports structured content.

A simple debug helper helps:

function assertRequired(value: unknown, name: string): asserts value {
  if (value === undefined || value === null || value === "") {
    throw new Error(`Missing required value: ${name}`);
  }
}

assertRequired(task, "task");
assertRequired(policyId, "policyId");

Prevention

• •Keep prompt templates and TypeScript types aligned.
  • •If your template uses {claimNumber}, define that field in an interface and reuse it everywhere.
• •Validate inputs at boundaries.
  • •Check request payloads before they hit AutoGen agents or tools.
• •Avoid ad-hoc string building for production prompts.
  • •Use one wrapper that owns templating so variable names stay consistent across your app.

If you want this error gone permanently, treat prompts like API contracts. The moment your template keys drift from your TypeScript payloads, AutoGen will fail exactly where it should.

Keep learning

• •The complete AI Agents Roadmap — my full 8-step breakdown
• •Free: The AI Agent Starter Kit — PDF checklist + starter code
• •Work with me — I build AI for banks and insurance companies

By Cyprian Aarons, AI Consultant at Topiax.