Arg Parser

When Apply

Use this skill when user needs to:

• Build type-safe CLI tools with argument parsing
• Add MCP (Model Context Protocol) server capabilities to existing CLIs
• Define flags with Zod schemas for runtime validation
• Create unified tools that work in both CLI and MCP modes
• Generate DXTs (Distributed Extensions) from CLI code
• Handle subcommands, flag inheritance, and dynamic flag registration
• Add interactive prompts to CLIs using @clack/prompts
• Build dual-mode CLIs (programmatic flags + interactive prompts)
• Create sequential prompts with dependencies between answers

Rules

Core Flag Rules

• ALWAYS use zodFlagSchema for flag definitions with Zod v4 syntax
• Import from #/core/types for interfaces IFlag IHandlerContext TParsedArgs
• For internal imports use #/* alias e.g. #/mcp/mcp-integration
• For local imports use ./ e.g. ./FlagManager
• Default flag type is string if not specified
• Mandate flags use mandatory property not required
• Environment variables: Flag > Env > Default priority

MCP Rules

• MCP tool names auto-sanitized to ^[a-zA-Z0-9_-]{1,64}$
• Console hijacking in MCP mode prevents STDOUT contamination
• Use createMcpLogger for data-safe logging in MCP context
• Output schemas supported in MCP protocol >= 2025-06-18

Interactive Prompt Rules

• Add prompt property to flags for interactive mode support
• Use promptSequence for explicit ordering (1 = first, 2 = second)
• Fallback to array order when promptSequence not specified
• Use --interactive or -i flag to trigger interactive mode (default promptWhen)
• Available prompt types: text, password, confirm, select, multiselect
• Prompt factory function receives IHandlerContext with promptAnswers from previous prompts
• Validation in prompts returns true for valid or string for error message
• TTY detection auto-falls back to flag-only mode in CI/pipes
• Cancel handler (Ctrl+C) calls onCancel callback or exits gracefully
• Subcommands with prompts need --interactive on BOTH root AND sub-parser
• Default Value Fallback: Flag defaultValue automatically used as prompt initial when not explicitly set
• Conditional Skipping: Use skip: true or skip: condition to skip prompts based on previous answers
• Multiselect Navigation: Use Space to toggle items, arrows to navigate

Workflow

1. Create CLI with flags

import { ArgParser } from "@alcyone-labs/arg-parser";

const parser = new ArgParser({
  appName: "My CLI",
  appCommandName: "my-cli",
  handler: async (ctx) => {
    console.log("Running with:", ctx.args);
  },
}).addFlags([
  {
    name: "input",
    options: ["--input", "-i"],
    type: String,
    description: "Input file",
  },
  {
    name: "verbose",
    options: ["--verbose", "-v"],
    type: Boolean,
    defaultValue: false,
  },
]);

parser.parse(process.argv);

2. Add MCP server

const parser = new ArgParser({...})
  .addFlags([...])
  .withMcp({
    serverInfo: { name: "my-cli-mcp", version: "1.0.0" },
    defaultTransport: { type: "stdio" }
  })

await parser.parse(process.argv)

3. Define flags with Zod schemas

.addFlag({
  name: "config",
  options: ["--config", "-c"],
  type: z.object({
    host: z.string(),
    port: z.number()
  }),
  description: "Configuration object"
})

4. Create unified tool (CLI + MCP)

parser.addTool({
  name: "process",
  description: "Process data",
  flags: [
    { name: "input", options: ["--input"], type: String, mandatory: true },
    { name: "output", options: ["--output"], type: String },
  ],
  handler: async (ctx) => ({ processed: true, input: ctx.args.input }),
  outputSchema: "successWithData",
});

5. Handle subcommands

const subParser = new ArgParser({
  appName: "My CLI",
  handler: async (ctx) => {
    /* subcommand logic */
  },
}).addFlags([
  /* subcommand flags */
]);

parser.addSubCommand({
  name: "sub",
  description: "Subcommand description",
  parser: subParser,
});

6. Use flag inheritance

new ArgParser({...}, undefined, FlagInheritance.AllParents)

7. Add interactive prompts

const parser = new ArgParser({
  appName: "deploy-tool",
  promptWhen: "interactive-flag",
  handler: async (ctx) => {
    if (ctx.isInteractive) {
      console.log("Interactive answers:", ctx.promptAnswers);
    }
    const env = ctx.args.environment || ctx.promptAnswers?.environment;
    console.log(`Deploying to ${env}...`);
  },
});

// Add --interactive flag
parser.addFlag({
  name: "interactive",
  options: ["--interactive", "-i"],
  type: "boolean",
  flagOnly: true,
  description: "Run in interactive mode",
});

// Add promptable flag
parser.addFlag({
  name: "environment",
  options: ["--env", "-e"],
  type: "string",
  prompt: async () => ({
    type: "select",
    message: "Select environment:",
    options: ["staging", "production"],
  }),
} as IPromptableFlag);

await parser.parse();

8. Sequential prompts with dependencies

parser.addFlag({
  name: "environment",
  options: ["--env"],
  type: "string",
  promptSequence: 1,
  prompt: async () => ({
    type: "select",
    message: "Select environment:",
    options: ["staging", "production"],
  }),
} as IPromptableFlag);

parser.addFlag({
  name: "version",
  options: ["--version"],
  type: "string",
  promptSequence: 2,
  prompt: async (ctx) => {
    // Access previous answer
    const env = ctx.promptAnswers?.environment;
    const versions = await fetchVersions(env);
    return {
      type: "select",
      message: `Select version for ${env}:`,
      options: versions,
    };
  },
} as IPromptableFlag);

9. Prompt when values are missing

parser.addSubCommand({
  name: "init",
  description: "Initialize repository",
  promptWhen: "missing", // Prompt if required flags missing
  parser: initParser,
  onCancel: () => console.log("Init cancelled"),
});

Examples

Example 1: Basic CLI

Input: my-cli --input ./data.json --verbose

// src/cli.ts
import { ArgParser } from "@alcyone-labs/arg-parser";

const parser = new ArgParser({
  appName: "Data Processor",
  appCommandName: "data-proc",
  handler: async (ctx) => {
    const { input, verbose } = ctx.args;
    console.log(`Processing: ${input}, verbose: ${verbose}`);
  },
}).addFlags([
  { name: "input", options: ["--input", "-i"], type: String, mandatory: true },
  {
    name: "verbose",
    options: ["--verbose", "-v"],
    type: Boolean,
    defaultValue: false,
  },
]);

parser.parse(process.argv);

Example 2: MCP Server with tools

Input: my-cli --s-mcp-serve

import { ArgParser, ArgParserError } from "@alcyone-labs/arg-parser";

const parser = new ArgParser({
  appName: "Search CLI",
  appCommandName: "search",
  handler: async (ctx) => ({ query: ctx.args.query }),
})
  .addFlags([
    {
      name: "query",
      options: ["--query", "-q"],
      type: String,
      mandatory: true,
    },
  ])
  .addTool({
    name: "search",
    description: "Search for items",
    flags: [
      { name: "term", options: ["--term"], type: String, mandatory: true },
      { name: "limit", options: ["--limit"], type: Number, defaultValue: 10 },
    ],
    handler: async (ctx) => ({ results: [`result for ${ctx.args.term}`] }),
    outputSchema: "successWithData",
  })
  .withMcp({
    serverInfo: { name: "search-cli", version: "1.0.0" },
    defaultTransport: { type: "stdio" },
  });

await parser.parse(process.argv);

Example 3: DXT bundling with config plugins

import { ArgParser } from "@alcyone-labs/arg-parser";
import { YamlConfigPlugin, globalConfigPluginRegistry } from "@alcyone-labs/arg-parser/config";

globalConfigPluginRegistry.register(new YamlConfigPlugin());

const parser = new ArgParser({
  appName: "Config App",
  appCommandName: "config-app",
})
  .addFlags([
    {
      name: "config",
      options: ["--config"],
      type: "string",
      env: "APP_CONFIG",
    },
  ])
  .withMcp({
    serverInfo: { name: "config-app", version: "1.0.0" },
    dxt: { include: ["config/", "assets/"] },
  });

await parser.parse(process.argv);

Example 4: Interactive CLI with prompts

Input: my-cli --interactive

import { ArgParser, type IPromptableFlag } from "@alcyone-labs/arg-parser";

const parser = new ArgParser({
  appName: "Deploy Tool",
  promptWhen: "interactive-flag",
  handler: async (ctx) => {
    if (ctx.isInteractive) {
      console.log("Deploying with:", ctx.promptAnswers);
    }
    const env = ctx.args.environment || ctx.promptAnswers?.environment;
    console.log(`Deploying to ${env}...`);
  },
});

parser.addFlag({
  name: "interactive",
  options: ["--interactive", "-i"],
  type: "boolean",
  flagOnly: true,
});

parser.addFlag({
  name: "environment",
  options: ["--env", "-e"],
  type: "string",
  prompt: async () => ({
    type: "select",
    message: "Select environment:",
    options: [
      { label: "Staging", value: "staging", hint: "Safe for testing" },
      { label: "Production", value: "production", hint: "Careful!" },
    ],
  }),
} as IPromptableFlag);

parser.addFlag({
  name: "version",
  options: ["--version", "-v"],
  type: "string",
  prompt: async (ctx) => {
    const env = ctx.promptAnswers?.environment;
    return {
      type: "select",
      message: `Select version for ${env}:`,
      options: ["1.0.0", "1.1.0", "2.0.0"],
    };
  },
} as IPromptableFlag);

await parser.parse();

Example 5: Password prompt with validation

parser.addFlag({
  name: "password",
  options: ["--password", "-p"],
  type: "string",
  prompt: async () => ({
    type: "password",
    message: "Enter password:",
  }),
} as IPromptableFlag);

parser.addFlag({
  name: "email",
  options: ["--email"],
  type: "string",
  prompt: async () => ({
    type: "text",
    message: "Enter email:",
    validate: (val) => {
      if (!val.includes("@")) return "Invalid email address";
      return true;
    },
  }),
} as IPromptableFlag);

Example 6: Default value fallback in prompts

parser.addFlag({
  name: "timeout",
  options: ["--timeout", "-t"],
  type: "number",
  defaultValue: 30, // Automatically used as initial in prompt
  prompt: async () => ({
    type: "text",
    message: "Enter timeout (seconds):",
    // No initial needed - uses defaultValue automatically
  }),
} as IPromptableFlag);

Example 7: Conditional prompt skipping

parser.addFlag({
  name: "configureAdvanced",
  options: ["--configure-advanced"],
  type: "boolean",
  promptSequence: 1,
  prompt: async () => ({
    type: "confirm",
    message: "Configure advanced options?",
    initial: false,
  }),
} as IPromptableFlag);

parser.addFlag({
  name: "advancedOptions",
  options: ["--advanced-options"],
  type: "string",
  promptSequence: 2,
  prompt: async (ctx) => ({
    type: "text",
    message: "Enter advanced options:",
    skip: !ctx.promptAnswers?.configureAdvanced, // Skip if false
  }),
} as IPromptableFlag);

Example 8: Multiselect with select all toggle

parser.addFlag({
  name: "modules",
  options: ["--modules", "-m"],
  type: "array",
  prompt: async () => ({
    type: "multiselect",
    message: "Select modules to install:",
    options: [
      { value: "auth", label: "Authentication", hint: "User login" },
      { value: "database", label: "Database", hint: "Data persistence" },
      { value: "api", label: "API", hint: "REST endpoints" },
      { value: "ui", label: "UI", hint: "User interface" },
    ],
    // Space to toggle, Enter to confirm
  }),
} as IPromptableFlag);

Example 9: Context-aware pre-configuration

Use CLI flags to pre-configure interactive prompts:

parser.addFlag({
  name: "global",
  options: ["--global", "-g"],
  type: "boolean",
  prompt: async (ctx) => ({
    type: "confirm",
    message: "Install globally?",
    initial: false,
    skip: ctx.args.global || ctx.args.local, // Skip if already specified
  }),
} as IPromptableFlag);

parser.addFlag({
  name: "packageManager",
  options: ["--package-manager", "-p"],
  type: "string",
  prompt: async (ctx) => {
    // Refine options based on pre-configured scope
    const isGlobal = ctx.args.global || ctx.promptAnswers?.global;
    const options = isGlobal ? ["npm", "yarn", "pnpm"] : ["npm", "yarn", "pnpm", "bun"];

    return {
      type: "select",
      message: "Package manager:",
      options,
      initial: ctx.args.packageManager, // Use CLI flag as default
    };
  },
} as IPromptableFlag);

Converted and distributed by TomeVault — claim your Tome and manage your conversions.