Lighter is a lightweight TypeScript framework for building AI agents. It handles the loop between model calls and tool execution so you can build an agent with just a few lines of code.
Inspired by Pi, Lighter keeps its core small while leaving room for customization. Its straightforward API makes it easy to get started, whatever your experience level.
Use it to:
- Call models through a shared interface for OpenAI, Claude, or DeepSeek.
- Run tools by giving the model access to your own functions for queries, calculations, and other tasks.
- Build interactions with streaming replies and conversation history maintained by your application.
- Customize behavior with lifecycle hooks that log requests, modify inputs, or process replies.
Getting started
Follow the quickstart to install Lighter, connect a model, and run your first agent. You need Node.js, an API key for a model provider, and an available model ID.
Core components
The smallest Lighter setup is Provider → Model → Agent:
| Component | Responsibility |
|---|---|
| Provider | Communicates with the model service and converts requests and responses |
| Model | Wraps model calls and runs hooks before and after them |
| Agent | Organizes messages and runs the loop between the model and tools |
Tools are optional. Without tools, the agent finishes after receiving a model reply. When the model requests tools, the agent executes them, returns their results, and calls the model again until it stops requesting tools.
Documentation
| Section | Topics |
|---|---|
| Getting started | Quickstart · Core concepts |
| Guides | Configuration · Tools · Conversation history · Streaming · Hooks · Errors |
| Providers | Built-in providers · Custom providers |
| Advanced | Use Model directly · Runtime limits |
| API reference | Agent · Model and Provider · Messages · Tool · Hooks · Errors |
AI agents can use llms.txt to find documentation on demand, or read the complete documentation.
Version and scope
This documentation covers Lighter 0.1.0, currently in alpha. Breaking API changes are possible.
Lighter provides the core loop. Your application handles conversation storage, loop limits, business permissions, and tool isolation.