Cloudflare Workers Developer Experience

Local development setup with Wrangler, Miniflare, and modern tooling.

Quick Start

# Create new project
bunx create-cloudflare@latest my-worker

# Or from scratch
mkdir my-worker && cd my-worker
bun init -y
bun add -d wrangler @cloudflare/workers-types

# Start local development
bunx wrangler dev

Secure Installation

Scaffolding tools like bunx create-cloudflare download and execute remote code. Before running, follow supply chain security best practices:

• Block post-install scripts — npm config set ignore-scripts true (or Bun: disabled by default)
• Cooldown period — Wait 7 days for new package versions to be vetted by the community
• Audit before installing — Run socket package score npm <pkg> or use socket npm install <pkg> to check packages

Load the dependency-upgrade skill for full security configuration including Socket CLI integration, cooldown setup, lockfile validation, and CI enforcement.

Essential wrangler.jsonc

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "name": "my-worker",
  "main": "src/index.ts",
  "compatibility_date": "2024-12-01",

  // Development settings
  "dev": {
    "port": 8787,
    "local_protocol": "http"
  },

  // Environment variables (non-secret)
  "vars": {
    "ENVIRONMENT": "development"
  },

  // Bindings
  "kv_namespaces": [
    { "binding": "KV", "id": "abc123", "preview_id": "def456" }
  ],

  "d1_databases": [
    { "binding": "DB", "database_id": "xyz789", "database_name": "my-db" }
  ],

  "r2_buckets": [
    { "binding": "BUCKET", "bucket_name": "my-bucket" }
  ]
}

Critical Rules

1. Always use wrangler dev for local testing - Simulates Cloudflare runtime accurately
2. Set compatibility_date - Controls runtime behavior, update quarterly
3. Use preview IDs for local dev - Separate from production bindings
4. Configure TypeScript properly - Use @cloudflare/workers-types
5. Enable source maps - Better error stacks in development

Top 6 Errors Prevented

Error	Symptom	Prevention
Module not found	Import errors on deploy	Set "moduleResolution": "bundler" in tsconfig
Binding undefined	env.KV is undefined locally	Add preview_id to KV namespace config
HMR not working	Changes not reflecting	Check port conflicts, use --local flag
D1 schema mismatch	Queries fail locally	Run migrations on local DB
Type errors	Missing binding types	Generate types with wrangler types
CORS issues	Browser blocking requests	Add CORS headers in dev handler

Local Development Workflow

# Start dev server (recommended)
bunx wrangler dev

# With live reload
bunx wrangler dev --live-reload

# Remote mode (use actual Cloudflare services)
bunx wrangler dev --remote

# Specify environment
bunx wrangler dev --env staging

# Custom port
bunx wrangler dev --port 3000

TypeScript Configuration

tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ES2022",
    "moduleResolution": "bundler",
    "lib": ["ES2022"],
    "types": ["@cloudflare/workers-types"],
    "strict": true,
    "noEmit": true,
    "skipLibCheck": true,
    "allowSyntheticDefaultImports": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Package.json Scripts

{
  "scripts": {
    "dev": "wrangler dev",
    "deploy": "wrangler deploy",
    "deploy:staging": "wrangler deploy --env staging",
    "deploy:production": "wrangler deploy --env production",
    "test": "vitest",
    "test:watch": "vitest --watch",
    "type-check": "tsc --noEmit",
    "lint": "eslint src/",
    "types": "wrangler types",
    "tail": "wrangler tail",
    "db:migrate": "wrangler d1 migrations apply DB",
    "db:studio": "wrangler d1 execute DB --local --command 'SELECT 1'"
  }
}

Debugging

Console Logging

// Development-only logging
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    if (env.ENVIRONMENT === 'development') {
      console.log('Request:', request.method, request.url);
      console.log('Headers:', Object.fromEntries(request.headers));
    }

    // Handler logic...
  }
};

Using wrangler tail

# Real-time logs from deployed worker
wrangler tail

# Filter by status
wrangler tail --status error

# Filter by method
wrangler tail --method POST

# JSON format for parsing
wrangler tail --format json

VS Code Debugging

.vscode/launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Wrangler Dev",
      "type": "node",
      "request": "launch",
      "runtimeExecutable": "bunx",
      "runtimeArgs": ["wrangler", "dev", "--inspector-port", "9229"],
      "skipFiles": ["<node_internals>/**"],
      "sourceMaps": true
    }
  ]
}

When to Load References

Load specific references based on the task:

• Setting up project? → Load references/local-development.md for complete setup guide
• Configuring wrangler? → Load references/wrangler-config.md for all configuration options
• Debugging issues? → Load references/debugging-tools.md for debugging techniques

Templates

Template	Purpose	Use When
templates/wrangler-config.jsonc	Complete wrangler config	Starting new project
templates/dev-script.ts	Development utilities	Adding dev helpers

Scripts

Script	Purpose	Command
scripts/dev-setup.sh	Initialize dev environment	./dev-setup.sh

Resources

• Wrangler CLI: https://developers.cloudflare.com/workers/wrangler/
• Configuration: https://developers.cloudflare.com/workers/wrangler/configuration/
• Local Development: https://developers.cloudflare.com/workers/testing/local-development/