I am looking at using this nodejs package and it is labelled as "zlib like" with no further information.

What, if any, are the implications of the license being zlib like?

  • 1
    Did you contact the authors of that package ? Commented Feb 24, 2020 at 18:05
  • @BasileStarynkevitch While it is useful to get a clear case about the licensing, I suggest to not make it expected to ask a question like this.
    – peterh
    Commented Feb 24, 2020 at 18:29
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    I wonder if this derives from Minizip for zlib whcih the author says is under the same terms as zlib. He did not put separate notices in the source files, though, so it makes sense that the notices might have gotten "misplaced" (though the letter of the license requires that you give the notice).
    – Brandin
    Commented Feb 25, 2020 at 8:35
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    If you can, I'd avoid it as just not quite clear enough. Of course you can also ask the author to upload a full license. Commented Feb 25, 2020 at 11:14
  • @BasileStarynkevitch I don't seem to have any way to contact the author and they have had no activity in 3 years. I might just be out of luck in that regard
    – Metagen
    Commented Feb 25, 2020 at 16:43

1 Answer 1


The package you link contains an actual version of zlib - which in turn comes with a readme which has a license section.

The zlib-license in itself is very permissive (basically a "do what you want") and only asks for attribution when you use it and indication of changes when you re-distribute changed source code.

This noted, the package itself is still of somewhat questionable license as it does not explicitly contain its own license and wording (especially the sentence on "The library has been entirely written by Jean-loup Gailly and Mark Adler; it does not include third-party code." obviously cannot be true - but the intention should be clear).

However, to be really legally safe you will still need to contact the authors and ask them to clarify... maybe send them a PR with an appropriately adopted version of the zlib license (don't be lengthy, the license also asks to not send lengthy legal documents ;) )

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    Seems I might just have to leave it as I have no way of contacting the author of the linked package.
    – Metagen
    Commented Feb 25, 2020 at 16:45
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    Yes, it's a risk-assessment which needs to be taken. Sadly, the authors very much likely wanted a "use it whereever, whenever and give us some credit but don't bother us" - and achieved somewhat the opposite by not including a clear license explicitly. One example more, that clear (and better even common licenses rather than your own), are worth A LOT or risk that your work was in vain. Commented Feb 25, 2020 at 16:53

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