What was Claude Code built with?

Claude Code was built with Ink, a React framework for building interactive command-line interfaces. It lets you build terminal UIs using the same component-based approach you’d use for building web apps.

The full tech stack includes TypeScript, React, Ink, Yoga (Meta’s layout engine), and Bun for building and packaging. The choice of TypeScript and React was intentional because Claude is already very good at working with these technologies, making it easier for the AI to help build and maintain its own codebase.

Codex, OpenAI’s CLI tool, was also originally built with Ink and React before they migrated to Rust for performance reasons. It’s become a popular choice for AI coding assistants because it gives you React’s component model and hooks in the terminal.

Here’s a simple example of what Ink code looks like:

import React from 'react';
import {Text} from 'ink';

const App = () => (
  <Text color="green">Hello from the terminal!</Text>
);

export default App;

If you’re familiar with React, you can jump right into building CLI apps with Ink. You get access to all the React features like hooks, state management, and component composition, but the output renders in your terminal instead of a browser.

I’ve used Ink for a few CLI projects and the developer experience is really nice. Being able to use React patterns for terminal UIs makes it much easier to build complex interactive tools.