Configure an agent

Only model is required when creating an Agent. Add tools, a system prompt, and lifecycle hooks as needed.

Set a system prompt

This example uses the environment variables and runner from the quickstart:

import {
  Agent, Model, OpenAIProvider, SystemMessage, UserMessage,
} from "@yong_xie/lighter";

const model = new Model(new OpenAIProvider(
  process.env.OPENAI_API_KEY!,
  process.env.OPENAI_MODEL!,
));

const agent = new Agent({
  model,
  // Set the role, task scope, and response style with SystemMessage.
  systemPrompt: new SystemMessage("You are a bookstore advisor. Answer questions briefly in English."),
});

const result = await agent.run({
  // Put the question for each run in messages.
  messages: [new UserMessage("Suggest three events for a bookstore on the moon.")],
});

console.log(result);

If you omit systemPrompt, the default is You are a helpful assistant. A custom value replaces this default.

Agent automatically prepends the system prompt to the context for each run. You do not need to add it again when maintaining conversation history.

Where configuration belongs

You cannot currently override the model or tools in an individual Agent request. Create another Agent when you need a different configuration.

Extend as needed

• Use Tool to let an agent run your functions.
• Use Hook to observe or modify a run.
• Adjust output length, reasoning, and other options in the provider configuration.

See Agent API for all parameters.