Brotli Compress and Decompress

What is Brotli?

Brotli is a compression format. A .br download and a lot of web traffic use it. The compressed bytes are not gzip, zlib, or raw DEFLATE, so those tools cannot open a Brotli stream.

This tool compresses bytes into a Brotli stream, or decompresses a Brotli stream back to the original bytes.

• Action: Compress or Decompress. Compress is the default. Decompress reads Brotli only. It does not guess other formats.
• Quality: a whole number from 0 to 11. 0 is the fastest and usually the largest. 11 spends much more time for a smaller result. The default is 6. The quality is ignored when you decompress.
• Window: compression writes a 4 MiB window, which every decoder opens. Decompression opens the standard windows up to 16 MiB. That is what the brotli command writes when you do not pass a window flag. A stream that uses the large-window extension, bigger than 16 MiB, is rejected.
• Input: pasted text up to 100 MiB, read as UTF-8, or a file up to 2 GiB. A file is read in pieces and is not held whole.
• Download name: optional. Compress adds .br. Decompress removes one trailing .br. If you upload a file and leave this blank, the upload name is used. Otherwise the download is named output.br or output.bin.
• The result is a file download. Expanding pasted text stops at 200 MiB. Expanding a file stops at 4 GiB.

Why quality stops at 6 by default

Quality 11 is what the brotli command uses when you do not pass a flag. On a multi-megabyte input that setting can stall a browser tab. Quality 6 is the same default this site uses for gzip, and it is the useful middle of the range: clearly smaller than quality 0, and much faster than 11.

A pasted run stops after 5 minutes. On a fast desktop, quality 11 takes well over a second per MiB, so a large paste is more comfortable at quality 9 or lower. Quality 10 takes about half as long. A file streams, and the clock restarts as output arrives.

The window this tool writes stays at 4 MiB on every quality. Decoding still opens a file whose window is 8 MiB or 16 MiB.

Are there alternatives?

Gzip is the format behind .gz files. zlib and raw DEFLATE are the same DEFLATE data with a different wrapper, or with no wrapper. Zstandard (.zst) is another modern codec. This page will not open any of those.

The brotli command on your computer does the same job for files larger than 2 GiB, and it can use the large-window extension when you ask it to.

Fun facts and more info

Jyrki Alakuijala, Zoltan Szabadka, and Evgenii Kliuchnikov published Brotli at Google. The format is RFC 7932.

The stream does not carry a checksum of the original bytes the way a gzip file does. A damaged or truncated stream fails to decode. That check does not tell you who created the file, and it is not a signature.

There is no standard way to tell a Brotli stream from other bytes by sniffing. This tool trusts the action you pick.