How to Compress WebP Images Online Losslessly

Before you start

Prepare the WebP file you want to reduce. Lossless online compression usually works best when the source is already a WebP image, but some browser tools also accept common formats and return a WebP result. Keep the original saved separately so you can compare it with the compressed version.

Check whether the tool states that it supports lossless WebP compression specifically. A general image optimizer may convert or re-encode the file, which can change the file format, pixel dimensions or transparency behavior. Also confirm whether processing happens in your browser or is uploaded to a remote service before you use a private or sensitive image.

Step-by-step instructions

• Open a browser-based image compressor that lists lossless WebP support.
• Select the lossless or WebP lossless mode when the tool offers a choice. If this mode is missing, the service may not support true lossless processing.
• Add the source image by dragging it into the upload area or using the file picker.
• Keep the original pixel dimensions and aspect ratio enabled if those options are present.
• Leave transparency enabled when the image contains transparent areas.
• Start the compression and wait for the tool to finish.
• Download the result and compare its file size with the original.

Tool interfaces vary. Some services process only one image at a time, while others offer batch output. If exact lossless behavior matters, use a mode that preserves the source data instead of a visually similar re-encode.

Check the output

Open the downloaded file and confirm that the dimensions match the source. Look at edges, small text, gradients and transparent areas, because these are the places where compression artifacts or transparency loss become visible first. If the tool provides an output file size, compare it with the input size to make sure the result is actually smaller.

Lossless WebP compression can produce a smaller file, but the amount depends on the source content. Photographic or noisy images may compress less than flat graphics. If the downloaded file is larger, the service may have re-encoded the image instead of applying lossless compression.

Common problems and next steps

The output has a different pixel size

Find the resize or dimensions option in the tool and make sure the width and height match the original. Some compressors apply a default maximum dimension unless you disable resizing.

Transparency became black or white

Check whether the output format is still WebP and whether the service includes an option to keep alpha transparency. If transparency is not preserved, use a different tool or keep the source as WebP instead of allowing conversion.

File size did not decrease

Try a different source file or check the compression mode. If the image was already well compressed, further lossless reduction may be minimal. A visually smaller file produced by lossy compression is not the same as a lossless result.

The tool asks for upload access

Read the service description before uploading private material. Browser-only tools process the file locally, while remote services send it to a server. If the processing location is unclear, use a non-sensitive test image first.