Deno Cliffy CLI Skill | Agent Skills

Deno Cliffy CLI

Build structured CLI tools in Deno with typed options, help text, and subcommands using @cliffy/command from JSR.

Quick Start

Add to deno.json:

{
  "imports": {
    "@cliffy/command": "jsr:@cliffy/command@^1.0.0-rc.7"
  }
}

Minimal CLI:

#!/usr/bin/env -S deno run --allow-all
import { Command } from "@cliffy/command";

const cli = new Command()
  .name("mytool")
  .version("0.1.0")
  .description("What the tool does");

cli
  .command("greet")
  .description("Say hello")
  .option("-n, --name <name:string>", "Who to greet", { default: "world" })
  .action(({ name }) => {
    console.log(`Hello, ${name}!`);
  });

await cli.parse(Deno.args);

Project Structure

For CLIs with multiple commands, use a commands/ directory:

project/
├── cli.ts           # Entry point, wires up commands
├── commands/
│   ├── build.ts     # export async function build(...)
│   ├── deploy.ts    # export async function deploy(...)
│   └── test.ts      # export async function runTests(...)
├── lib/             # Shared utilities
│   └── helpers.ts
└── deno.json        # Tasks + imports

Each command file exports a single async function. The CLI entry point imports and wires them.

Key Patterns

Lazy Imports for Heavy Dependencies

When a command depends on something heavy (Playwright, Puppeteer, large npm packages), use dynamic import in the action handler. This prevents loading the dependency for unrelated commands.

cli
  .command("scrape")
  .action(async ({ output }) => {
    const { scrape } = await import("./commands/scrape.ts");
    await scrape(output);
  });

Critical when dependencies read env vars or spawn processes at import time.

deno.json Task Integration

Wire subcommands to deno task with per-command permissions:

{
  "tasks": {
    "cli": "deno run --allow-all cli.ts",
    "build": "deno run --allow-read=. --allow-write=. cli.ts build",
    "scrape": "deno run --allow-all cli.ts scrape"
  }
}

Use --allow-all only when genuinely needed. Pass extra flags with --: deno task build -- --watch.

npm Packages in Deno

Import npm packages via npm: specifier or map them in deno.json:

{
  "imports": {
    "handlebars": "npm:handlebars@^4.7.8"
  },
  "nodeModulesDir": "auto"
}

Set "nodeModulesDir": "auto" when npm packages need to read their own files from disk (templates, assets, partials). Without this, packages using __dirname or fs.readFileSync relative to their install path will fail.

Reference

For detailed API patterns (option types, command nesting, global options, error handling), see the Patterns Reference Guide.

Agent Skills: Deno Cliffy CLI

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