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Efficient Compression Tool vs Zopfli: catalog facts
Efficient Compression Tool	Zopfli
Free Free and open source under the Apache 2.0 licence.	Free Free and open source from Google.
Windows, Command line	Command line
Handles PNG, JPEG, GZIP and ZIP in one tool Adjustable levels to trade speed against file size	Smaller output than standard gzip at its highest level Output readable by any gzip, zlib or deflate decoder
Command-line only Limited to four file formats	Much slower than ordinary compressors Compresses only; decompression uses standard tools
Downloadable app	Downloadable app
Open source	Open source
License: Apache-2.0	License not stated
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.