Fiddler and Brotli

Regular readers of my blog know how excited I am about Google’s new open compression engine, Brotli. Support is in Firefox 44 Nightly already and is expected for other browsers. Because Brotli is used inside the WOFF2 font format, many clients already have the compression code and just need to expose it in a new way.

Yesterday’s Fiddler release supports Brotli. To expose Brotli inside Fiddler, download and place brotli.exe inside Fiddler’s %ProgramFiles(x86)%\Fiddler2\Tools\ subfolder and restart to see it appear on the Transformer tab:


After installation, Content-Encoding: br is also supported by Fiddler’s Decode toolbar option, as well as the encoding Infobar:


Test servers are starting to come online for Brotli, particularly now that Google has released a new Brotli module for the nginx web server. For now, you can try downloading this image:

Brotli didn't decode

…that is served with brotli encoding. If your browser supports brotli, it will render a star; if not, the image will appear broken unless you set the Decode option in Fiddler’s toolbar so Fiddler will decode the image before the browser sees it.

-Eric Lawrence

Published by ericlaw

Impatient optimist. Dad. Author/speaker. Created Fiddler & SlickRun. PM @ Microsoft 2001-2012, and 2018-2022, working on Office, IE, and Edge. Now a SWE on Microsoft Defender Web Protection. My words are my own, I do not speak for any other entity.

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