Considering using flot for graphs in plugin and a little lost with dependencies and licensing here.

  1. WordPress repository demands GPLv2-compatible.
  2. flot is under MIT license, which is GPL-compatible.
  3. flot uses excanvas (for IE compatibility) under Apache License 2.0 which is compatible to GPLv3, but not v2.

So is or is not flot compatible to repository?

Aside - I had started wiki-style question if you want to suggest and discuss alternative libraries Graphing libraries for WordPress

  • 1
    I would say yes, but WP.org seems to be a bit anal on GPLv2-and-only-GPLv2. It's like they can't be bothered to understand that there are OSS licenses that are more free than what the FSF promotes. Mar 19, 2011 at 15:05
  • @Peter Rowell as an answer please. :) I am also looking into alternatives, but it seems like excanvas is common dependency for charting libraries :( So question is more broad...
    – Rarst
    Mar 19, 2011 at 15:10
  • @Mike I rolled back your edit, the links are already contained in question and you used outdated one for excanvas
    – Rarst
    Mar 19, 2011 at 19:00
  • @Rarst - Okay, but I didn't see the links before. I see the newer links now. Mar 19, 2011 at 19:29
  • @MikeSchinkel I made anchors larger to make them more obvious. Color contrast on links is low. :(
    – Rarst
    Mar 19, 2011 at 19:39

5 Answers 5


The easiest thing I think is to ask wordpress.org if it's possible that they host your plugin with GPL v3+ compatibility. Probably they say yes. Give it a try, the discussion was very new back in the end of January so points of views might be a bit more settled these days.

IMHO there is not really something to loose if they allow GPL v3+ plugins in the repository.

In case they find code that is cool for core, they can ask. I mean, who would not relicense code then if it's possible. It's nothing as static as it's often said.

The next thing you can do is to ask the excanvas project if you can use their code under MIT as well. Probably they do allow you that. Ask them. Probably that's already possible, because flot ships under MIT and it incorporates the excanvas code in it's package. But you should always ask on your own.

  • Well, at moment repository docs explicitly say GPLv2. :( I think flot includes excanvas without issues because AL2 is compatible with MIT. It's AL2 with GPLv2 that is the issue in context of WP.
    – Rarst
    Mar 19, 2011 at 19:45
  • Well last time I checked the repository docs, they linked the general compatibly list on gnu.org which was GPL v3 based. I guess no-one really knows. It's just some politics and probably you can make your voice heard.
    – hakre
    Mar 19, 2011 at 20:00
  • I am resolved to stay as far from WP politics as I can. I had my share and realized it's not healthy (for me personally at least) to be involved. :)
    – Rarst
    Mar 19, 2011 at 20:34
  • Yeah, I hope we can get some repository plugin sometime now - I would love something interacting with stuff hosted on github - so this is actually easier to grasp - Plugin and Theme Repository Configuration - Who wants to help?
    – hakre
    Mar 20, 2011 at 8:34

As of May 2012 plugin repo rules have been updated, allowing Apache License 2.0 and some other previously incompatible licenses:

The plugin directory’s licensing guidelines have been updated. The guidelines will now allow code that is licensed under (or compatible with) version 3 of the GPL.

The guidelines still encourage use of “GPLv2 or later,” the same license as WordPress. However, we understand that many open source libraries use other licenses that are nonetheless compatible, such as GPLv2 only, GPLv3, and Apache 2.0.



Automattic's Stats plugin uses Open Flash Chart, which is licensed under LGPL, so you might want to take a look at that.

  • Thank you for suggestion, but I will probably start another question (community wiki) on graphing libraries and WP. For this one mostly interested if I can use excanvas in for-repository plugin or definitely not.
    – Rarst
    Mar 19, 2011 at 16:11
  • Question live - Graphing libraries for WordPress.
    – Rarst
    Mar 19, 2011 at 16:23
  • 1
    Don't base your career on this, but I'm pretty sure no one will notice.
    – scribu
    Mar 19, 2011 at 17:33
  • 1
    It's client work so it is not my place to take such risk. If it was for my personal stuff I'd likely go with it indeed. :)
    – Rarst
    Mar 19, 2011 at 17:59
  • 1
    – scribu
    Mar 19, 2011 at 23:13

As requested, here it is as an answer. :-)

I would say yes, but WP.org seems to be a bit anal on GPLv2-and-only-GPLv2. It's like they can't be bothered to understand that there are OSS licenses that are more free than what the FSF promotes.


I'm quite certain that now wordpress.com itself uses flot - see the WordPress blog sexy stats post. I'd say that's good enough reason to ignore any wordpress.org complaints.

  • 1
    wordpress.com can use whatever they want since they are not redistributing most of their code and so under no obligation to stay away from non-GPL pieces. Ignoring something that potentially can get one's client's plugin obliterated from repository would be unwise as for me.
    – Rarst
    Feb 9, 2012 at 19:25
  • very good point. Also quite interestingly the JetPack plugin they have released with Wordpress stats, doesn't appear to use flot, at least I can't find any reference to it and the reference to the flot library in wordpress.com stats is obvious.
    – icc97
    Feb 10, 2012 at 13:24
  • Yes - while flot is used on wordpress.com site, none (as far as I know) of the plugins by wordpress.com or automattic or around there use it.
    – Rarst
    Feb 10, 2012 at 19:34

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