Free online image compressor.

The best free image compressor online.

Most free image compressors have a catch: they upload your images to a server, limit you to a handful of files, slap watermarks on the output, or ask for your email before letting you download. ToolBox Image is different because it does not have a server. The entire compressor — decoding, re-encoding, resizing, metadata stripping — runs in your browser via WebAssembly. Your images stay on your machine, period.

This architecture means there are no file size limits (other than what your device can handle in memory), no queue caps, and no premium tier. You can drag in a folder of 200 high-resolution photos and compress them all at once. The compressor uses Mozilla's mozJPEG for JPEG, Google's libwebp for WebP, and libaom for AVIF — all compiled to WebAssembly for native-level performance. It also supports format conversion, so you can drop a folder full of HEIC photos from an iPhone and export them all as JPEG or WebP in one batch.

Why use an online image compressor?

Images make up the majority of bytes on the average web page. Compressing them is the single highest-impact optimisation you can make — it improves page load times, reduces bandwidth costs, and creates a better experience for visitors on slow connections. Beyond the web, compressed images take up less storage space on your phone or computer and upload faster to social media, email attachments, and cloud services. A typical photo from a modern smartphone is 4-8 MB. Compressed for the web, the same photo is 200-600 KB — a 90% reduction with no visible quality loss.

ToolBox Image handles all major formats in a single interface. You do not need separate tools for JPEG, PNG, and WebP — just drop everything into one queue, pick your settings, and download the results. Each image gets its own before-and-after comparison so you can verify quality before saving. For format-specific needs, check our dedicated JPEG compressor, PNG compressor, WebP compressor, and AVIF compressor pages.

Privacy you can trust

Every image you compress stays on your device. There is no server to upload to, no database to store your files, and no third-party analytics tracking what you compress. Because the encoder runs locally via WebAssembly, the only copies of your images are the ones you choose to save. This is especially important for sensitive documents, design assets, and personal photos — you get the utility of a powerful compressor with the privacy of a desktop application.

Processing is parallelized across all available CPU cores via Web Workers. A batch of 50 images compresses in seconds. The interface shows real-time progress, individual file comparisons, and a running tally of total bytes saved. There is no registration, no email collection, no limits on usage.

Tips for best results

Use the Auto preset for most images — it picks the right format and quality for each file individually. For design assets that need pixel-perfect output, switch to Lossless mode. Use target-size mode when you need to hit a specific file size for a platform like Discord (Discord compressor) or email (100KB compressor). For large batches, the bulk compressor maintains folder structure and processes everything in parallel.