LZ4 Compress and Decompress

What is LZ4?

LZ4 is a compression format built for speed. It compresses and decompresses much faster than gzip, and the files come out larger in exchange. Files usually end in .lz4.

This tool compresses bytes into an LZ4 frame, or decompresses an LZ4 frame back to the original bytes.

• Action: Compress or Decompress. Compress is the default. Decompress reads an LZ4 frame, including the legacy lz4 -l format. Several frames written one after another are joined into one output. It does not guess other formats.
• There is no level setting. This tool always uses the standard fast mode.
• 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 .lz4. Decompress removes one trailing .lz4. If you upload a file and leave this blank, the upload name is used. Otherwise the download is named output.lz4 or output.bin.
• The result is a file download. Expanding pasted text stops at 200 MiB. Expanding a file stops at 4 GiB. A frame that declares a larger original size is rejected before decoding starts.

Why LZ4 is used so much

When processor time matters more than the last few megabytes, LZ4 is the usual pick. File systems such as ZFS, databases such as ClickHouse, and the Linux kernel use it to compress data as it moves.

In our tests on a desktop computer, 100 MiB of text compressed in about 0.6 seconds and came out at about half its size. Decompressing it took about 0.2 seconds.

Are there alternatives?

Zstandard (.zst) is a little slower and makes noticeably smaller files. Gzip (.gz) opens almost everywhere. Each has its own tool on this site. This page opens only LZ4 frames.

The lz4 command's older legacy format (lz4 -l) opens here. Raw LZ4 blocks stored inside another file format do not, because they have no frame header.

The lz4 command on your computer does the same job for files larger than 2 GiB, and it offers slower high-compression levels.

Fun facts and more info

Yann Collet released LZ4 in 2011. He later created Zstandard.

An LZ4 frame can carry an xxHash checksum of the original bytes, which catches a damaged or truncated download. It does not tell you who made the file, and it is not a signature.