deno-core

# Deno Core Best Practices

## When to Use This Skill

Use this skill for ALL Deno TypeScript development:
- Setting up new Deno projects
- Writing Deno applications or libraries
- Configuring build, test, and deployment
- Working with dependencies and imports

## Core Deno Philosophy

### One Tool, Zero Dependencies
- Deno is the **only tool you need** for TypeScript development
- Built-in tooling: typecheck, lint, format, test, coverage, benchmark
- **Avoid `node_modules` at all costs** - reduce supply chain attack surface
- No need for: tsc, eslint, prettier, jest, vitest, webpack, etc.

### TypeScript Excellence
- **Strict TypeScript adherence** - not just "TS support"
- **Bleeding-edge TypeScript features by default** - no flags, no config needed
- No compilation step - just run your code
- Target **ES2024+** with Stage 3 TC39 proposals

### Security First
- Explicit permissions model (no implicit file system or network access)
- Supply chain security through minimal external dependencies
- First-class support for modern security patterns

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## Language & Compiler

### TypeScript Configuration

- **Do not use `tsconfig.json`** - Deno uses `deno.json(c)` as the single source of truth
- Type-checking powered by `deno check` / `deno test` - **do not** rely on external `tsc`
- Default module format is **ESM only** - no CommonJS interop
- Prefer Deno's **runtime-provided types** (`Deno.*`, Web APIs, Fetch, URLPattern) over polyfills

### Strictest Compiler Settings

Always use the strictest possible settings in `deno.json`:

```json
{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "exactOptionalPropertyTypes": true
  }
}
```

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## Configuration & Tasks

### deno.json - Single Source of Truth

Use `deno.json` or `deno.jsonc` as the single configuration file for:
- Compiler options
- Linting and formatting rules
- Task