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# Development Server
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Start NestJS applications in development mode with hot reloading, debugging support, and comprehensive configuration options. The development server provides an efficient workflow for rapid application development and testing.
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## Capabilities
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### Start Command
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Launches your NestJS application with development-focused features and extensive customization options.
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```bash { .api }
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# Start application
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nest start [app] [options]
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# Options:
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-c, --config [path]                 # Path to nest-cli configuration file
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-p, --path [path]                   # Path to tsconfig file
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-w, --watch                        # Run in watch mode (live-reload)
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-b, --builder [name]               # Builder to be used (tsc, webpack, swc)
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--watchAssets                      # Watch non-ts (e.g., .graphql) files mode
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-d, --debug [hostport]             # Run in debug mode (with --inspect flag)
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--webpack                          # Use webpack for compilation (deprecated, use --builder)
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--webpackPath [path]               # Path to webpack configuration
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--type-check                       # Enable type checking (when SWC is used)
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--tsc                             # Use typescript compiler for compilation
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--sourceRoot [sourceRoot]          # Points at the root of the source code
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--entryFile [entryFile]            # Path to the entry file
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-e, --exec [binary]                # Binary to run (default: "node")
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--preserveWatchOutput             # Use "preserveWatchOutput" option when using tsc watch mode
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--shell                           # Spawn child processes within a shell (default: true)
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--no-shell                        # Do not spawn child processes within a shell
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--env-file [path]                 # Path to an env file (.env) to be loaded
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```
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**Usage Examples:**
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```bash
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# Basic development server
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nest start
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# Start with watch mode (hot reload)
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nest start --watch
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# Start specific app in monorepo
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nest start api-gateway
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# Start with debug mode
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nest start --debug
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nest start --debug 0.0.0.0:9229
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# Start with asset watching
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nest start --watch --watchAssets
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# Start with specific builder
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nest start --builder webpack
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nest start --builder swc --type-check
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# Start with environment file
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nest start --env-file .env.development
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# Start with custom entry point
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nest start --entryFile src/main.ts
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# Start with custom binary
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nest start --exec "node --max-old-space-size=4096"
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```
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## Development Features
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### Watch Mode
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Automatically restart the application when files change:
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```bash { .api }
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# Enable hot reloading
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nest start --watch
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# Watch with asset monitoring
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nest start --watch --watchAssets
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```
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**Watched File Types:**
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- TypeScript files (.ts)
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- JavaScript files (.js)
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- JSON configuration files
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- GraphQL schema files (with --watchAssets)
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- Protocol buffer definitions (with --watchAssets)
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### Debug Mode
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Enable Node.js debugging with Inspector protocol:
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```bash { .api }
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# Debug on default port (9229)
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nest start --debug
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# Debug on specific host:port
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nest start --debug 0.0.0.0:9229
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nest start --debug localhost:9229
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# Debug with watch mode
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nest start --debug --watch
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```
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**Debug Configuration:**
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- Enables `--inspect` flag automatically
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- Supports Chrome DevTools
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- Compatible with VS Code debugger
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- Works with watch mode for continuous debugging
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### Environment Configuration
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Load environment variables from files:
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```bash { .api }
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# Single environment file
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nest start --env-file .env.development
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# Multiple environment files
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nest start --env-file .env --env-file .env.local
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```
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## Build System Integration
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### TypeScript Compiler
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```bash { .api }
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# Use TypeScript compiler
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nest start --builder tsc --watch
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# With preserved watch output
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nest start --builder tsc --watch --preserveWatchOutput
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```
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### Webpack Development Server
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```bash { .api }
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# Use Webpack with HMR
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nest start --builder webpack --watch
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# Custom webpack configuration
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nest start --builder webpack --webpackPath webpack.dev.js
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```
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### SWC for Fast Compilation
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```bash { .api }
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# Use SWC for fast development builds
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nest start --builder swc --watch
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# SWC with type checking
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nest start --builder swc --type-check --watch
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```
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## Process Management
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### Shell Configuration
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Control how child processes are spawned:
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```bash { .api }
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# Use shell (default)
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nest start --shell
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# No shell spawning
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nest start --no-shell
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```
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### Custom Binary Execution
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Specify the runtime binary and options:
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```bash { .api }
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# Default Node.js
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nest start --exec node
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# Node with memory optimization
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nest start --exec "node --max-old-space-size=4096"
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# Node with experimental features
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nest start --exec "node --experimental-modules"
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```
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## Project Structure Support
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### Monorepo Applications
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```bash { .api }
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# Start specific application
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nest start api-gateway
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nest start user-service
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nest start payment-service
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# Start with project-specific config
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nest start api-gateway --config apps/api-gateway/nest-cli.json
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```
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### Custom Entry Points
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```bash { .api }
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# Custom entry file
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nest start --entryFile src/main.ts
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nest start --entryFile apps/api/src/main.ts
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# Custom source root
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nest start --sourceRoot src
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nest start --sourceRoot apps/api/src
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```
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## Configuration Files
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### nest-cli.json Development Settings
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```json
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{
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  "collection": "@nestjs/schematics",
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  "sourceRoot": "src",
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  "compilerOptions": {
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    "builder": "webpack",
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    "typeCheck": true,
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    "assets": ["**/*.proto", "**/*.graphql"],
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    "watchAssets": true
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  },
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  "generateOptions": {
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    "spec": false
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  }
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}
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```
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### Environment File Loading
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Supported environment file formats:
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```bash
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# .env files
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.env
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.env.local
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.env.development
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.env.development.local
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```
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Environment file example:
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```env
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NODE_ENV=development
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PORT=3000
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DATABASE_URL=postgresql://localhost:5432/nestjs_dev
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LOG_LEVEL=debug
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```
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## Performance Optimization
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### Fast Development Builds
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```bash { .api }
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# Fastest startup with SWC
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nest start --builder swc --watch
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# Balance speed and features with Webpack
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nest start --builder webpack --watch
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# Full type safety with TypeScript
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nest start --builder tsc --watch --preserveWatchOutput
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```
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### Memory Management
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```bash { .api }
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# Increase Node.js memory limit
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nest start --exec "node --max-old-space-size=8192"
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# Enable garbage collection optimization
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nest start --exec "node --optimize-for-size"
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```
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## Development Workflow Integration
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### Common Development Commands
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```bash { .api }
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# Standard development workflow
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nest start --watch --debug
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# Full-featured development with assets
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nest start --watch --watchAssets --debug --env-file .env.development
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# Fast iteration development
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nest start --builder swc --watch --type-check
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```
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### IDE Integration
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The development server works seamlessly with:
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- VS Code with Node.js debugging
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- WebStorm with built-in Node.js support
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- Chrome DevTools for debugging
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- Any editor with Language Server Protocol support
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## Error Handling
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### Invalid Builder Options
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```bash
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# Invalid builder name
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nest start --builder invalid
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# Error: Invalid builder option: invalid. Available builders: tsc, webpack, swc
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```
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### Process Exit Handling
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The CLI properly handles process termination and cleanup:
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- Graceful shutdown on SIGTERM/SIGINT
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- Child process cleanup
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- File watcher cleanup
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- Port release
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### Error Recovery
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In watch mode, the CLI recovers from compilation errors:
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- Continues watching after TypeScript errors
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- Restarts on successful compilation
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- Preserves debug connections when possible