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

Always use wrangler dev for local testing - Simulates Cloudflare runtime accurately
Set compatibility_date - Controls runtime behavior, update quarterly
Use preview IDs for local dev - Separate from production bindings
Configure TypeScript properly - Use @cloudflare/workers-types
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/

cloudflare-workers-dev-experience

Cloudflare Workers Developer Experience

Quick Start