⁓ bargs ⁓

"Ex argumentis, veritas"
by @boneskull

Install

npm install @boneskull/bargs

Why bargs?

Most argument parsers make you choose: either a simple API with weak types, or a complex and overengineered DSL. bargs provides a combinator-style API for building type-safe CLIs—composable schema definitions with full type inference.

Also: this is the only argument parser I know of that comes with frickin' themes. Themes, dogg.

Quick Start

A CLI with an optional command and a couple options:

import { bargs, opt, pos } from '@boneskull/bargs';

await bargs('greet', { version: '1.0.0' })
  .globals(
    opt.options({
      name: opt.string({ default: 'world' }),
      loud: opt.boolean({ aliases: ['l'] }),
    }),
  )
  .command(
    'say',
    pos.positionals(pos.string({ name: 'message', required: true })),
    ({ positionals, values }) => {
      const [message] = positionals;
      const greeting = `${message}, ${values.name}!`;
      console.log(values.loud ? greeting.toUpperCase() : greeting);
    },
    'Say a greeting',
  )
  .defaultCommand('say')
  .parseAsync();

$ greet Hello --name Alice --loud
HELLO, ALICE!

Usage

Type-Safe by Construction

Each helper returns a fully-typed definition:

import { opt, pos } from '@boneskull/bargs';

const verbose = opt.boolean({ aliases: ['v'] });
// Type: BooleanOption & { aliases: ['v'] }

const level = opt.enum(['low', 'medium', 'high'], { default: 'medium' });
// Type: EnumOption<'low' | 'medium' | 'high'> & { default: 'medium' }

const file = pos.string({ name: 'file', required: true });
// Type: StringPositional & { name: 'file', required: true }

When you build a CLI with these, the result types flow through automatically—options with defaults or required: true are non-nullable.

Composable

Options and positionals can be merged using callable parsers:

import { opt, pos } from '@boneskull/bargs';

// Create separate parsers
const options = opt.options({
  verbose: opt.boolean({ aliases: ['v'] }),
  output: opt.string({ aliases: ['o'], default: 'stdout' }),
});

const positionals = pos.positionals(
  pos.string({ name: 'input', required: true }),
);

// Merge them: positionals(options) combines both
const parser = positionals(options);
// Type: Parser<{ verbose: boolean | undefined, output: string }, [string]>

Simple CLI

For a CLI without subcommands, use .globals() with merged options and positionals, then handle the result yourself:

import { bargs, opt, pos } from '@boneskull/bargs';

// Merge options and positionals into one parser
// when a positional is variadic, it becomes an array within the result
const parser = pos.positionals(pos.variadic('string', { name: 'text' }))(
  opt.options({
    uppercase: opt.boolean({ aliases: ['u'], default: false }),
  }),
);

const { values, positionals } = await bargs('echo', {
  description: 'Echo text to stdout',
  version: '1.0.0',
})
  .globals(parser)
  .parseAsync();

const [words] = positionals;
const text = words.join(' ');
console.log(values.uppercase ? text.toUpperCase() : text);

Command-Based CLI

For a CLI with multiple subcommands:

import { bargs, merge, opt, pos } from '@boneskull/bargs';

await bargs('tasks', {
  description: 'A task manager',
  version: '1.0.0',
})
  .globals(
    opt.options({
      verbose: opt.boolean({ aliases: ['v'], default: false }),
    }),
  )
  .command(
    'add',
    // Use merge() to combine positionals with command-specific options
    merge(
      opt.options({
        priority: opt.enum(['low', 'medium', 'high'], { default: 'medium' }),
      }),
      pos.positionals(pos.string({ name: 'text', required: true })),
    ),
    ({ positionals, values }) => {
      const [text] = positionals;
      console.log(`Adding ${values.priority} priority task: ${text}`);
      if (values.verbose) console.log('Verbose mode enabled');
    },
    'Add a task',
  )
  .command(
    'list',
    opt.options({
      all: opt.boolean({ default: false }),
    }),
    ({ values }) => {
      console.log(values.all ? 'All tasks' : 'Pending tasks');
    },
    'List tasks',
  )
  .defaultCommand('list')
  .parseAsync();

$ tasks add "Buy groceries" --priority high --verbose
Adding high priority task: Buy groceries
Verbose mode enabled

$ tasks list --all
All tasks

Nested Commands (Subcommands)

Commands can be nested to arbitrary depth. The only limit is your contempt for your users. Use the factory pattern:

import { bargs, opt, pos } from '@boneskull/bargs';

await bargs('git')
  .globals(opt.options({ verbose: opt.boolean({ aliases: ['v'] }) }))
  // Factory pattern: receives a builder with parent globals already typed
  .command(
    'remote',
    (remote) =>
      remote
        .command(
          'add',
          pos.positionals(
            pos.string({ name: 'name', required: true }),
            pos.string({ name: 'url', required: true }),
          ),
          ({ positionals, values }) => {
            const [name, url] = positionals;
            // values.verbose is fully typed! (from parent globals)
            if (values.verbose) console.log(`Adding ${name}: ${url}`);
          },
          'Add a remote',
        )
        .command('remove' /* ... */)
        .defaultCommand('add'),
    'Manage remotes',
  )
  .command('commit', commitParser, commitHandler) // Regular command
  .parseAsync();

$ git --verbose remote add origin https://github.com/...
Adding origin: https://github.com/...

$ git remote remove origin

The factory function receives a CliBuilder that already has parent globals typed, so all nested command handlers get full type inference for merged global + command options. See examples/nested-commands.ts for a full example.

API

bargs(name, options?)

Create a CLI builder.

.globals(parser)

Set global options and transforms that apply to all commands.

bargs('my-cli').globals(opt.options({ verbose: opt.boolean() }));
// ...

.command(name, parser, handler, description?)

Register a command. The handler receives merged global + command types.

.command(
  'build',
  opt.options({ watch: opt.boolean() }),
  ({ values }) => {
    // values has both global options AND { watch: boolean }
    console.log(values.verbose, values.watch);
  },
  'Build the project',
)

.command(name, factory, description?)

Register a nested command group using a factory function. The factory receives a builder that already has parent globals typed, giving full type inference in nested handlers.

bargs('main')
  .globals(opt.options({ verbose: opt.boolean() }))
  .command(
    'nested',
    (nested) =>
      nested
        .command('foo', fooParser, ({ values }) => {
          // values.verbose is typed correctly!
        })
        .command('bar', barParser, barHandler),
    'Nested commands',
  )
  .parseAsync();

.defaultCommand(name)

Or .defaultCommand(parser, handler)

Set the command that runs when no command is specified.

// Reference an existing command by name
.defaultCommand('list')

// Or define an inline default
.defaultCommand(
  pos.positionals(pos.string({ name: 'file' })),
  ({ positionals }) => console.log(positionals[0]),
)

.parse(args?) / .parseAsync(args?)

Parse arguments and execute handlers.

• .parse() - Synchronous. Throws if any transform or handler returns a Promise.
• .parseAsync() - Asynchronous. Supports async transforms and handlers.

// Async (supports async transforms/handlers)
const result = await bargs('my-cli').globals(...).parseAsync();
console.log(result.values, result.positionals, result.command);

// Sync (no async transforms/handlers)
const result = bargs('my-cli').globals(...).parse();

Option Helpers

import { opt } from '@boneskull/bargs';

opt.string({ default: 'value' }); // --name value
opt.number({ default: 42 }); // --count 42
opt.boolean({ aliases: ['v'] }); // --verbose, -v
opt.boolean({ aliases: ['v', 'verb'] }); // --verbose, --verb, -v
opt.enum(['a', 'b', 'c']); // --level a
opt.array('string'); // --file x --file y
opt.array(['low', 'medium', 'high']); // --priority low --priority high
opt.count(); // -vvv → 3

Option Properties

Aliases

Options can have both short (single-character) and long (multi-character) aliases:

opt.options({
  verbose: opt.boolean({ aliases: ['v', 'verb'] }),
  output: opt.string({ aliases: ['o', 'out'] }),
});

All of these are equivalent:

$ my-cli -v                # verbose: true
$ my-cli --verb            # verbose: true
$ my-cli --verbose         # verbose: true
$ my-cli -o file.txt       # output: "file.txt"
$ my-cli --out file.txt    # output: "file.txt"
$ my-cli --output file.txt # output: "file.txt"

For non-array options, using both an alias and the canonical name throws an error:

$ my-cli --verb --verbose
Error: Conflicting options: --verb and --verbose cannot both be specified

For array options, values from all aliases are merged. Single-character aliases and the canonical name are processed first (in command-line order), then multi-character aliases are appended:

opt.options({
  files: opt.array('string', { aliases: ['f', 'file'] }),
});

$ my-cli --file a.txt -f b.txt --files c.txt
# files: ["b.txt", "c.txt", "a.txt"]
# (-f and --files first, then --file appended)

Boolean Negation (--no-)

All boolean options automatically support a negated form --no-<flag> to explicitly set the option to false:

$ my-cli --verbose      # verbose: true
$ my-cli --no-verbose   # verbose: false
$ my-cli                # verbose: undefined (or default)

If both --flag and --no-flag are specified, bargs throws an error:

$ my-cli --verbose --no-verbose
Error: Conflicting options: --verbose and --no-verbose cannot both be specified

In help output, booleans with default: true display as --no-<flag> (since that's how users would turn them off):

opt.options({
  colors: opt.boolean({ default: true, description: 'Use colors' }),
});
// Help output shows: --no-colors  Use colors  [boolean] default: true

opt.options(schema)

Create a parser from an options schema:

const parser = opt.options({
  verbose: opt.boolean({ aliases: ['v'] }),
  output: opt.string({ default: 'out.txt' }),
});
// Type: Parser<{ verbose: boolean | undefined, output: string }, []>

Positional Helpers

import { pos } from '@boneskull/bargs';

pos.string({ required: true }); // <file>
pos.number({ default: 8080 }); // [port]
pos.enum(['dev', 'prod']); // [env]
pos.variadic('string'); // [files...]

Positional Properties

pos.positionals(...defs)

Create a parser from positional definitions:

const parser = pos.positionals(
  pos.string({ name: 'source', required: true }),
  pos.string({ name: 'dest', required: true }),
);
// Type: Parser<{}, [string, string]>

Use variadic for rest arguments (must be last):

const parser = pos.positionals(pos.variadic('string', { name: 'files' }));
// Type: Parser<{}, [string[]]>

Merging Parsers

Use merge() to combine multiple parsers into one:

import { merge, opt, pos } from '@boneskull/bargs';

const combined = merge(
  opt.options({
    priority: opt.enum(['low', 'medium', 'high'], { default: 'medium' }),
  }),
  pos.positionals(pos.string({ name: 'task', required: true })),
);
// Type: Parser<{ priority: 'low' | 'medium' | 'high' }, [string]>

You can merge as many parsers as needed—options are merged (later overrides earlier), and positionals are concatenated.

Alternatively, parsers can be merged by calling one with the other:

const options = opt.options({ priority: opt.enum(['low', 'medium', 'high']) });
const positionals = pos.positionals(
  pos.string({ name: 'task', required: true }),
);

// These are equivalent:
const combined1 = positionals(options);
const combined2 = options(positionals);

Use whichever style you find more readable.

Transforms

Use map() to transform parsed values before they reach your handler:

import { bargs, map, opt } from '@boneskull/bargs';

const globals = map(
  opt.options({
    config: opt.string(),
    verbose: opt.boolean({ default: false }),
  }),
  ({ values, positionals }) => ({
    positionals,
    values: {
      ...values,
      // Add computed properties
      timestamp: new Date().toISOString(),
      configLoaded: !!values.config,
    },
  }),
);

await bargs('my-cli')
  .globals(globals)
  .command(
    'info',
    opt.options({}),
    ({ values }) => {
      // values.timestamp and values.configLoaded are available
      console.log(values.timestamp);
    },
    'Show info',
  )
  .parseAsync();

Transforms are fully type-safe—the return type becomes the type available in handlers.

Async Transforms

Transforms can be async:

const globals = map(
  opt.options({ url: opt.string({ required: true }) }),
  async ({ values, positionals }) => {
    const response = await fetch(values.url);
    return {
      positionals,
      values: {
        ...values,
        data: await response.json(),
      },
    };
  },
);

CamelCase Option Keys

If you prefer camelCase property names instead of kebab-case, use the camelCaseValues transform:

import { bargs, map, opt, camelCaseValues } from '@boneskull/bargs';

const { values } = await bargs('my-cli')
  .globals(
    map(
      opt.options({
        'output-dir': opt.string({ default: '/tmp' }),
        'dry-run': opt.boolean(),
      }),
      camelCaseValues,
    ),
  )
  .parseAsync(['--output-dir', './dist', '--dry-run']);

console.log(values.outputDir); // './dist'
console.log(values.dryRun); // true

The camelCaseValues transform:

• Converts all kebab-case keys to camelCase (output-dir → outputDir)
• Preserves keys that are already camelCase or have no hyphens
• Is fully type-safe—TypeScript knows the transformed key names

Epilog

By default, bargs displays your package's homepage and repository URLs (from package.json) at the end of help output. URLs become clickable hyperlinks in supported terminals.

// Custom epilog
bargs('my-cli', {
  epilog: 'For more info, visit https://example.com',
});

// Disable epilog entirely
bargs('my-cli', { epilog: false });

Theming

Customize help output colors with built-in themes or your own:

// Use a built-in theme: 'default', 'mono', 'ocean', 'warm'
bargs('my-cli', { theme: 'ocean' });

// Disable colors entirely
bargs('my-cli', { theme: 'mono' });

The ansi export provides common ANSI escape codes for styled terminal output:

import { ansi } from '@boneskull/bargs';

bargs('my-cli', {
  theme: {
    colors: {
      command: ansi.bold,
      flag: ansi.brightCyan,
      positional: ansi.magenta,
      // ...
    },
  },
});

Available theme color slots:

[!TIP] You don't need to specify all color slots. Missing colors fall back to the default theme.

Shell Completion

bargs can generate shell completion scripts for bash, zsh, and fish. Enable it with the completion option:

bargs('my-cli', {
  completion: true,
  version: '1.0.0',
});

Then generate and install the completion script for your shell:

Bash

# Add to ~/.bashrc (or ~/.bash_profile on macOS)
my-cli --completion-script bash >> ~/.bashrc
source ~/.bashrc

Zsh

# Add to ~/.zshrc
my-cli --completion-script zsh >> ~/.zshrc
source ~/.zshrc

# Or save to a file in your $fpath
my-cli --completion-script zsh > ~/.zsh/completions/_my-cli

Fish

# Save to completions directory
my-cli --completion-script fish > ~/.config/fish/completions/my-cli.fish

What Gets Completed

Once installed, pressing Tab will complete:

• Commands and subcommands (including nested commands and aliases)
• Options (--verbose, -v, --no-verbose for booleans)
• Enum values for options and positionals with defined choices
• Global options at any command level

$ my-cli <TAB>
build  test  lint

$ my-cli build --target <TAB>
dev  staging  prod

$ my-cli --<TAB>
--verbose  --config  --help  --version

See examples/completion.ts for a complete example.

Advanced Usage

Error Handling

bargs exports some Error subclasses:

import {
  bargs,
  BargsError,
  HelpError,
  ValidationError,
} from '@boneskull/bargs';

try {
  await bargs('my-cli').parseAsync();
} catch (error) {
  if (error instanceof ValidationError) {
    // Config validation failed (e.g., invalid schema)
    // i.e., "you screwed up"
    console.error(`Config error at "${error.path}": ${error.message}`);
  } else if (error instanceof HelpError) {
    // Likely invalid options, command or positionals;
    // re-throw to trigger help display
    throw error;
  } else if (error instanceof BargsError) {
    // General bargs error
    console.error(error.message);
  }
}

Programmatic Help

Generate help text programmatically:

import { generateHelp, generateCommandHelp } from '@boneskull/bargs';

// These require the internal config structure—see source for details
const helpText = generateHelp(config);
const commandHelp = generateCommandHelp(config, 'migrate');

Hyperlink Utilities

Create clickable terminal hyperlinks (OSC 8):

import { link, linkifyUrls, supportsHyperlinks } from '@boneskull/bargs';

// Check if terminal supports hyperlinks
if (supportsHyperlinks()) {
  // Create a hyperlink
  console.log(link('Click me', 'https://example.com'));

  // Auto-linkify URLs in text
  console.log(linkifyUrls('Visit https://example.com for more info'));
}

[!TIP] bargs already automatically links URLs in --help output if the terminal supports hyperlinks.

Additional Theme Utilities

import {
  ansi, // ANSI escape codes
  createStyler, // Create a styler from a theme
  defaultTheme, // The default theme object
  stripAnsi, // Remove ANSI codes from string
  themes, // All built-in themes
} from '@boneskull/bargs';

// Create a custom styler
const styler = createStyler({ colors: { flag: ansi.green } });
console.log(styler.flag('--verbose'));

// Strip ANSI codes for plain text output
const plain = stripAnsi('\x1b[32m--verbose\x1b[0m'); // '--verbose'

Low-Level Utilities

The handle(parser, fn) function is exported for advanced use cases where you need to create a Command object outside the fluent builder. It's mostly superseded by .command(name, parser, handler).

Dependencies

bargs has zero (0) dependencies. Only Node.js v20+.

Motivation

I've always reached for yargs in my CLI projects. However, I find myself repeatedly doing the same things; I have a sort of boilerplate in my head, ready to go (requiresArg: true and nargs: 1, amirite?). I don't want boilerplate in my head. I wanted to distill my chosen subset of yargs' behavior into a composable API. And so bargs was begat.

License

Copyright © 2025 Christopher "boneskull" Hiller. Licensed under the Blue Oak Model License 1.0.0.