Fast, private image compression that runs entirely in your browser. No uploads, no servers — your images never leave your device.

slimg decodes and re-encodes images using WebAssembly codecs (jSquash) across a pool of web workers, so you can batch-compress dozens of files in parallel without freezing the UI.

• 100% client-side — all processing happens in your browser via WASM. Nothing is uploaded.
• JPEG, PNG & WebP — decode and encode any combination, or keep the original format.
• Format conversion — turn PNGs into WebP, JPEGs into PNG, and so on.
• Quality control — adjustable quality for JPEG/WebP encoding.
• Lossless PNG optimization — powered by oxipng with selectable optimization levels.
• Resize on the fly — optional max width/height (never upscales).
• Parallel batch processing — a worker pool sized to your CPU keeps compression fast and the page responsive.
• One-click download — grab files individually or export everything as a .zip.
• Drag & drop with instant before/after size and savings summary.
• Internationalized — English, 中文, and 日本語 out of the box.

• React 19 + TypeScript
• jSquash WASM codecs (JPEG, PNG, oxipng, WebP)
• Comlink for ergonomic web worker RPC
• Zustand for state
• client-zip for in-browser zip export
• i18next for localization
• Vite+ toolchain (Vite, Rolldown, Oxlint, Oxfmt)

This project uses the Vite+ toolchain via the global vp CLI.

# install dependencies
vp install

# start the dev server
vp dev

# build for production
vp build

# preview the production build
vp preview

Prefer pnpm scripts? pnpm dev, pnpm build, and pnpm preview wrap the same commands.

1. Files dropped into the browser are read as ArrayBuffers and dispatched to a CodecPool.
2. The pool spreads jobs across navigator.hardwareConcurrency - 1 web workers, transferring buffers (zero-copy) to each worker.
3. Each worker lazily loads only the WASM codecs it needs and caches them, so repeated formats pay the init cost only once.
4. Decoded ImageData is optionally resized, then re-encoded to the target format and handed back to the UI as a Blob.

Because everything is local, slimg works offline and handles sensitive images without ever transmitting them.

src/
├── core/          # worker pool, types, download/zip helpers
├── worker/        # codec worker + per-format encode/decode modules
├── components/    # DropZone, SettingsPanel, TaskList, ...
├── store/         # Zustand task store
└── i18n/          # i18next setup + locale files (en, zh, ja)

Issues and pull requests are welcome. Before submitting, please run:

vp check   # format, lint, and type-check
vp test    # run tests

MIT