Deno

Overview

Deno is a secure JavaScript/TypeScript runtime with built-in tooling including a formatter, linter, test runner, and bundler. It features a permissions model that restricts file, network, and environment access by default, native TypeScript support without transpilation, and full web standards compatibility.

Instructions

• When creating servers, use

  Deno.serve()

  for high-performance HTTP handling with Web Standards Request/Response, and enable parallel workers with

  deno serve --parallel

  for multi-core utilization.
• When configuring security, specify permissions explicitly (

  --allow-read

  ,

  --allow-net

  ,

  --allow-env

  ) scoped to specific paths, hosts, or variable names. Never deploy with

  --allow-all

  .
• When managing dependencies, use JSR (

  jsr:

  ) for versioned, type-checked packages,

  npm:

  specifier for npm packages, and configure import maps in

  deno.json

  for clean paths.
• When writing tests, use

  Deno.test()

  with

  @std/assert

  assertions,

  @std/testing

  for mocking, and

  deno test --coverage

  for coverage reports. Deno's sanitizers detect resource leaks automatically.
• When building CLI tools, use

  deno compile

  to produce standalone executables that cross-compile for Linux, macOS, and Windows with no runtime dependency.
• When deploying to the edge, use Deno Deploy with Deno KV for key-value storage,

  Deno.cron()

  for scheduled tasks, and queues for background processing.
• When using Deno KV, structure keys hierarchically (

  ["users", id, "profile"]

  ), use

  atomic()

  for transactions, and configure TTL with

  expireIn

  for automatic expiration.

Examples

Example 1: Build a REST API with Deno KV

User request: "Create an API with Deno that stores data in Deno KV"

Actions:

1. Create HTTP server with

   Deno.serve()

   and route matching
2. Open KV store with

   Deno.openKv()

   and define key structure
3. Implement CRUD operations using

   kv.get()

   ,

   kv.set()

   , and

   kv.atomic()

4. Set explicit permissions in

   deno.json

   task definitions

Output: A secure API with embedded key-value storage, ready for Deno Deploy.

Example 2: Compile a CLI tool for distribution

User request: "Create a Deno CLI tool that can be distributed as a single binary"

Actions:

1. Build the CLI with argument parsing using

   @std/cli

2. Add file and network permissions scoped to required resources
3. Write tests with

   Deno.test()

   and run with

   deno test

4. Compile to standalone binaries with

   deno compile --target

   for each platform

Output: Cross-platform standalone executables with no runtime dependency.

Guidelines

• Always specify permissions explicitly in production; never deploy with

  --allow-all

  .
• Use

  deno.json

  imports map for clean import paths instead of raw URLs.
• Prefer JSR (

  jsr:

  ) over URL imports for versioned, type-checked, immutable packages.
• Use

  npm:

  specifier for npm packages instead of CDN URLs.
• Run

  deno fmt

  and

  deno lint

  in CI for zero-config formatting and linting.
• Use

  Deno.serve()

  over third-party frameworks for simple APIs; it is faster and lighter.
• Compile to standalone binary with

  deno compile

  for distribution with no runtime dependency.