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CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Repository Overview
+
+Uppy is a modular JavaScript file uploader that integrates seamlessly with any application. It's built using a monorepo structure with Yarn workspaces, Turbo for build orchestration, and Biome for linting/formatting.
+
+## Development Commands
+
+### Core Commands
+- `yarn build` - Build all packages (uses Turbo)
+- `yarn build:watch` - Watch mode for building packages
+- `yarn test` - Run tests for all packages
+- `yarn test:watch` - Run tests in watch mode
+- `yarn typecheck` - Type checking across all packages
+- `yarn check` - Run Biome linting and formatting
+- `yarn check:ci` - Run Biome in CI mode (no writes)
+
+### Development Server
+- `yarn dev` - Start development server (from private/dev workspace)
+- `yarn dev:with-companion` - Start dev server with Companion backend
+- `yarn start:companion` - Start only the Companion server
+
+### Single Test Execution
+To run tests for a specific package:
+```bash
+yarn workspace @uppy/[package-name] test
+# Example: yarn workspace @uppy/core test
+```
+
+### Individual Package Development
+```bash
+yarn workspace @uppy/[package-name] build
+```
+
+## Architecture
+
+### Monorepo Structure
+- `packages/@uppy/` - Core Uppy packages (plugins, utilities)
+- `packages/uppy/` - Main bundle package
+- `examples/` - Example implementations for various frameworks
+- `private/` - Internal development tools
+
+### Core Architecture
+- **Uppy Core** (`@uppy/core`) - Main class that manages plugins, state, and events
+- **Plugins** - Modular components for different functionalities:
+  - **UI Plugins**: Dashboard, Drag & Drop, File Input, Webcam, etc.
+  - **Provider Plugins**: Google Drive, Dropbox, Instagram, etc. (require Companion)
+  - **Uploader Plugins**: Tus (resumable), XHR Upload, AWS S3, etc.
+  - **Utility Plugins**: Golden Retriever (recovery), Thumbnail Generator, etc.
+
+### Plugin Types
+1. **Acquirer** - Gets files (File Input, Webcam, Google Drive)
+2. **Modifier** - Modifies files (Image Editor, Compressor)
+3. **Uploader** - Uploads files (Tus, XHR, AWS S3)
+4. **Presenter** - Shows UI (Dashboard, Progress Bar, Status Bar)
+5. **Orchestrator** - Manages workflow
+6. **Logger** - Handles logging
+
+### Key Packages
+- `@uppy/core` - Main Uppy class and plugin system
+- `@uppy/dashboard` - Complete UI with file management
+- `@uppy/companion` - Server-side component for remote providers
+- `@uppy/companion-client` - Client for communicating with Companion
+- `@uppy/utils` - Shared utilities
+- `@uppy/components` - Headless Preact components (with framework wrappers)
+
+## Build System
+
+### Turbo Configuration
+The build system uses Turbo (turbo.json) for task orchestration:
+- Builds have dependency ordering (`dependsOn: ["^build"]`)
+- TypeScript builds output to `lib/` and `dist/` directories
+- CSS builds process SCSS files to CSS
+- Special handling for the main `uppy` package bundle
+
+### TypeScript Configuration
+- Shared config in `tsconfig.shared.json`
+- Individual packages have `tsconfig.json` and `tsconfig.build.json`
+- Build outputs include declaration files (.d.ts) and source maps
+
+## Code Standards
+
+### Linting and Formatting
+- **Biome** is used for linting and formatting (replaces ESLint/Prettier)
+- Configuration in `biome.json`
+- Use single quotes, semicolons as needed
+- 2-space indentation
+
+### Framework Integration
+- **Preact** for UI components with framework wrappers generated for React, Vue, Svelte
+- **TypeScript** throughout the codebase
+- Components in `@uppy/components` use Tailwind CSS with `uppy:` prefix
+
+### Plugin Development
+- All plugins extend `BasePlugin` or `UIPlugin`
+- Plugins must have unique IDs and specify their type
+- State management through Uppy's store system
+- Event-driven architecture using namespace-emitter
+
+## Testing
+
+### Test Framework
+- **Vitest** for unit tests (migrated from Jest)
+- **Vitest Browser Mode** for browser testing (migrated from Cypress)
+- Unit tests use `.test.{ts,tsx}` extensions and browser tests `.browser.test.{ts,tsx}`
+
+### Running Tests
+- Tests run in parallel across packages via Turbo
+- Examples also include tests (React, Vue, SvelteKit examples)
+- Use `yarn test` for development
+
+## Companion Server
+
+The Companion server enables integration with remote file sources:
+- Handles OAuth flows for providers like Google Drive, Dropbox
+- Proxies file downloads to avoid CORS issues
+- Provides search functionality for providers
+- Located in `packages/@uppy/companion/`
+
+## Important Notes
+
+- Never commit sensitive information (API keys, tokens)
+- Follow existing code conventions and patterns within each package
+- Use the `@uppy/utils` package for shared functionality
+- UI components should be accessible and support internationalization
+- Always run `yarn check` and `yarn typecheck` before committing
+- When adding a new component to `@uppy/components`, you have to run `yarn migrate:components` from root.
+  This is not needed for changing existing components.