modular_cli_sdk 0.3.4

Command-centric SDK for building modular CLIs with Dart — Command/Input/Output contract, structured errors, output formatting, and automatic TTY detection. Built on cli_router.

modular_cli_sdk

Command-centric SDK for building modular CLIs with Dart. Define Command classes (input → validate → execute → output), connect them to CLI routes, and get automatic output formatting with JSON and plain text modes.

Also see: modular_api — the HTTP counterpart with the same architecture.

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Quick start

import 'package:cli_router/cli_router.dart';
import 'package:modular_cli_sdk/modular_cli_sdk.dart';

void main(List<String> args) async {
  final cli = ModularCli();

  // Root-level commands (no module prefix)
  cli.command<VersionInput, VersionOutput>(
    'version',
    (req) => VersionCommand(VersionInput.fromCliRequest(req)),
    description: 'Print version info',
  );

  // Module-scoped commands, declaring their contract
  cli.module('greetings', (m) {
    m.command<HelloInput, HelloOutput>(
      'hello',
      (req) => HelloCommand(HelloInput.fromCliRequest(req)),
      description: 'Say hello to someone',
      params: HelloInput.params,
    );
  });

  final code = await cli.run(args);
  exit(code);
}

dart run bin/main.dart version
# version: 0.2.0

dart run bin/main.dart version --json
# {"version": "0.2.0"}

dart run bin/main.dart greetings hello --name World
# greeting: Hello, World!

dart run bin/main.dart greetings hello --name World --json
# {"greeting": "Hello, World!"}

See example/ for a full working example with root commands and two modules (greetings + math).

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Help and the command contract

Each command declares its parameters once, on its Input. The SDK introspects its own command registry to render help — the CLI counterpart of the OpenAPI document modular_api generates from its registered use cases.

class HelloInput extends Input {
  final String name;
  HelloInput({required this.name});

  static final params = [
    CliParam.string('name', abbr: 'n', defaultValue: 'World',
        description: 'Who to greet'),
  ];

  factory HelloInput.fromCliRequest(CliRequest req) =>
      HelloInput(name: req.flagString('name')!); // already resolved and defaulted

  @override
  List<CliParam> get schemaFields => params;

  @override
  Map<String, dynamic> toJson() => {'name': name};
}

Declaring is parsing. The same declaration that help renders is the one the framework enforces before your Input reads a flag: it resolves -n to --name, applies the declared default, coerces --a abc to a validation error instead of a silent 0, rejects an option nobody declared, and checks allowed values. Help therefore cannot describe a contract the CLI does not actually apply. A command that declares no params keeps parsing its arguments by hand and is neither described nor enforced.

Help is a success, not an error:

mycli                      # no args  → command list on stdout, exit 0
mycli help                 #          → same
mycli --help               #  or -h   → same
mycli greetings hello -h   #          → only that command's contract, exit 0
mycli greetings --help     #          → every command in the module, exit 0
mycli help --json          #          → the full contract catalog (help.json), exit 0

mycli bogus                # unknown  → error + catalog on stderr, exit 64
mycli math add --b 7       # rejected → error + that command's usage on stderr, exit 7

help --json is the machine-readable twin of the text help: every command with its route, description and parameters (name, aliases, type, required, default, allowed), plus the global options.

A help command you register yourself always wins over the built-in one.

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Features

• Command<I, O> — pure business logic, no I/O concerns
• CliParam — a command's declared contract: renders help and enforces parsing
• Native help — help, no args, --help/-h on stdout with exit 0; help --json for machines
• Input / Output — typed DTOs for command I/O
• CommandException — structured errors with code, message, exit code, and retryable flag
• ModularCli + ModuleBuilder — module registration and routing
• Root commands — register commands without a module prefix via cli.command()
• --json global flag — machine-readable JSON output
• --quiet global flag — suppress informational messages
• TTY detection — automatic format selection
• Semantic exit codes — 0 (OK), 1 (error), 4 (not found), 5 (unauthorized), 7 (validation), 64 (usage)
• Built on cli_router — GNU flags, middleware, modular mounting

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Installation

dart pub add modular_cli_sdk

Or add it manually to pubspec.yaml:

dependencies:
  modular_cli_sdk: ^0.3.0

dart pub add modular_cli_sdk

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Error handling

@override
Future<MyOutput> execute() async {
  final ticket = await repository.findById(input.ticketId);
  if (ticket == null) {
    throw CommandException(
      code: 'TICKET_NOT_FOUND',
      message: 'Ticket #${input.ticketId} not found',
      exitCode: ExitCode.notFound,
    );
  }
  return ShowTicketOutput(ticket: ticket);
}

Error: Ticket #42 not found [TICKET_NOT_FOUND]

With --json:

{"error": "TICKET_NOT_FOUND", "message": "Ticket #42 not found", "exitCode": 4, "isRetryable": false}

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Architecture

dart:io / Process           — I/O primitive
       ↓
cli_router                  — routing engine (routes, GNU flags, middleware)
       ↓
modular_cli_sdk             — SDK/framework
       ↓
ModularCli → Module → Command → Business Logic → Output → formatted terminal output

• Command layer — pure logic, independent of output format
• Output adapter — turns Output into JSON or plain text based on flags/TTY
• Middleware — cross-cutting concerns (logging, auth, metrics)

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Documentation

• API reference — generated dartdoc on pub.dev
• doc/architecture.md — architecture overview and symmetry with modular_api
• doc/roadmap.md — planned features for upcoming releases
• AGENTS.md — framework guide (AI-optimized)

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Compile to executable

dart compile exe bin/main.dart -o build/my-cli

The compiled binary includes the Dart runtime and runs without the SDK installed.

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License

MIT © ccisne.dev