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Zopfli vs Efficient Compression Tool: catalog facts
Zopfli	Efficient Compression Tool
Free Free and open source from Google.	Free Free and open source under the Apache 2.0 licence.
Command line	Windows, Command line
Smaller output than standard gzip at its highest level Output readable by any gzip, zlib or deflate decoder	Handles PNG, JPEG, GZIP and ZIP in one tool Adjustable levels to trade speed against file size
Much slower than ordinary compressors Compresses only; decompression uses standard tools	Command-line only Limited to four file formats
Downloadable app	Downloadable app
Open source	Open source
License not stated	License: Apache-2.0
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.