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JPEG Optimizer: Shrink JPG File Size with mozjpeg

Re-encode JPEGs with mozjpeg to cut file size at near-identical quality. Runs fully in your browser, no uploads, and never returns a bigger file.

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Privacy First
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How It Works

Most JPEGs carry more bytes than the picture actually needs. Cameras, phones, and editor "Save As" dialogs pick safe, conservative encoding settings, which leaves real headroom to recompress. This tool decodes your JPEG and re-encodes it with mozjpeg, an encoder tuned to fit the same image into fewer bytes using trellis quantization and optimized Huffman tables. You get a smaller .jpg that looks the same at normal viewing sizes. Be clear on the trade-off: this is a lossy re-encode, not a lossless rewrite. Every JPEG save discards some data, and recompressing does it one more time. At the quality level used here the loss is hard to spot, but it is real, so keep your original if you plan to edit or re-export later. Optimizing a JPEG that is already tightly compressed gives little extra savings. Everything runs locally with WebAssembly. Your file is read into memory in the browser, processed on your machine, and handed back as a download; nothing is uploaded to a server. There is also a guard built in: if the re-encoded file is not actually smaller than the one you fed in, you get your original back unchanged. This tool will not hand you a file bigger than you started with.

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Key Features

  • No file uploads required - works offline
  • 100% privacy focused - client-side processing
  • Browser powered - no software installation
  • Fast processing - WebAssembly technology
  • Free forever - no premium accounts

Supported File Formats

.jpg .jpeg

Output Format: JPG Optimized

Technical Specifications

input Format JPEG / JPG (Joint Photographic Experts Group)
output Format Optimized JPEG (.jpg), same format in, same format out
compression Type Lossy re-encode via mozjpeg (trellis quantization, optimized Huffman tables)
quality Retention Visually near-identical at standard viewing sizes; a second lossy pass, not lossless
color Space Support RGB / YCbCr; embedded ICC profiles and EXIF are dropped during re-encoding
max Resolution Limited only by your device's memory
processing Time Instant, runs in your browser

Key Benefits

  • Smaller JPEGs from mozjpeg's encoder, which often beats editor defaults at the same visual quality
  • Runs 100% in your browser with no uploads, so private and client images stay on your device
  • Never returns a larger file: keeps your original if re-encoding does not help
  • No quality slider to fiddle with, tuned for a safe size-to-quality balance
  • Strips EXIF and GPS metadata as a side effect, leaving cleaner files for publishing
  • No account, no watermark, and no per-file cap beyond your device's memory

Common Use Cases

  • Trimming hero and product photos before publishing to cut page weight
  • Recompressing camera and phone JPEGs that were saved at high quality
  • Reducing image payloads to improve Core Web Vitals and mobile load times
  • Lowering bandwidth and storage costs for image-heavy sites and galleries
  • Shrinking screenshots and photos to fit email or upload size limits
  • Removing embedded location and camera metadata before sharing photos publicly

Pro Tips

  • Keep your original JPEG; this is a lossy pass and discarded detail cannot be recovered later
  • Do not repeatedly re-optimize the same file, since each round is another lossy save with little extra savings
  • If the output comes back the same size, your file was already well compressed, which is expected
  • Need to keep EXIF or GPS data? Save a copy of the original first, because metadata is not carried into the output
  • For logos, icons, or screenshots with flat color and sharp edges, a PNG optimizer or WebP will usually beat JPEG

Frequently Asked Questions

No. It re-encodes the image with mozjpeg, which is a lossy step. The visual difference is very hard to notice at typical sizes, but a small amount of detail is discarded. If you need pixel-for-pixel fidelity, keep your original and use this only for the web-facing copy.
It depends entirely on how the file was first saved. JPEGs exported at high quality, or by older encoders, often shrink noticeably; files that are already tightly compressed shrink little or not at all. There is no fixed percentage, and anyone promising one is guessing. If mozjpeg cannot beat the original size, the tool returns your original untouched.
No. After re-encoding, the tool compares the new size against the original and gives you only the smaller of the two. In the worst case you download the exact file you uploaded, never a bigger one.
No. The whole process runs client-side in your browser using WebAssembly. The image is read into local memory, optimized, and returned as a download. It never leaves your device, which makes this safe for private photos, client work, and internal screenshots.
Yes. The file is fully decoded to pixels and re-encoded, so embedded metadata such as EXIF, GPS coordinates, and ICC color profile tags is not carried into the output. That is a privacy win when publishing online, but save the original if you specifically need to keep camera or location data.
You can, but mozjpeg compresses more efficiently than the default JPEG encoders in most editors. At a comparable visual quality it produces smaller files thanks to trellis quantization and optimized entropy coding, so you get a better size-to-quality result without manually hunting for the right slider value.
This tool takes a JPEG as input. If you have a PNG, use the PNG optimizer (which is truly lossless) or convert to JPEG first. Re-optimizing a JPEG that was already converted from another format works fine, but remember each JPEG save is a fresh lossy pass.
The practical limit is your device's available memory, since the entire image is decoded in the browser. Large photos work fine on a modern laptop or phone; extremely high-resolution files may be slow or fail on memory-constrained devices.