Introduction

What decopin-cli is, and the idea behind it.

Build CLIs the way Next.js builds web apps: file conventions, JSX output, and types that come from your declarations. TypeScript + Bun.

Output is JSX. There is no React; decopin ships its own small renderer.

// app/hello/cmd.tsx
import { Line, Text, type CmdProps } from 'decopin-cli';

export default function Command({ args, options }: CmdProps<'hello'>) {
  return (
    <Line>
      <Text bold color="green">
        hello, {args.name}
      </Text>
    </Line>
  );
}

$ bun run build
$ ./dist/index.js hello world
hello, world

The idea

A CLI has more inputs than argv. It reads stdin, or does not. It depends on environment variables it never lists. Its error output changes shape two subcommands down. In most CLIs these live inside the code, unstated, and the type checker cannot see any of them.

decopin gives each of them a file with a fixed name. Every file you add does two things: it changes what the command does, and it changes the type of CmdProps<'…'> the next time decopin build or decopin dev runs. What you leave out is not guessed.

And once the inputs are declared instead of implied, everything that reads a declaration comes for free: --help, shell completion, the TypeScript types, and an MCP server the CLI already is — mycli __mcp, with no tool definition to write and no second description to keep in sync.

There are three kinds of files, and they differ in where they may go:

Continue with Setup, then Project structure.