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If yes, what precautions should I take?

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With an MIT/X11-licensed product:

  • you CAN:
    • re-use the code freely for your own use,
    • re-use the code freely for non-commercial AND commercial re-distribution, whether in source or binary form.
  • you CANNOT:
    • claim authorship of the software,
    • thus you cannot attack the original author for using or publishing his original version.

So, yes, you CAN use MIT/X11-licensed plug-ins in your commercial application.

MIT/X11 is basically a simple contract that says:

  • Person or company X created Y.
  • Y belongs to X, but X is granting you the right to use it and do whatever you want with it.
  • X cannot be held accountable for anything that goes downhill with what you do with Y.
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    If a part of my software uses the source code under MIT license and another part is written by me, how do I have to state that in my app? In each file or in the license "some of the files are taken from NNN (the original author) and changed by me"?
    – Incerteza
    Apr 3, 2015 at 14:50
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    @Alex: again, IANAL, but I think the right way is to provide a file containing license information stating for which parts of your product it is used. But I'd also indeed had a comment where you use the code and give a reference to the author and source site, both for the the copyright claim but also to facilitate traceability if you need to look at that code later down the line.
    – haylem
    Apr 7, 2015 at 7:33
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    @haylem Hi. Can you expand on the you cannot claim authorship of the software. How this relate to the entire product? So if I release a closed source product, that includes a MIT licensed piece of code, this product has two authors?
    – this
    Nov 22, 2015 at 19:46
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    @this: Copyright and authorship are inalienable, and are not the same as a license. A license (like MIT) lays the terms for the use and distribution by a 3rd party. Copyright is implicit and inalienable. Though the MIT/X11 license gives you the right to reuse (in full or partly, modified or unaltered) a piece of sofware licensed that way, and to redistribute it (in both commercial or non-commercial forms, closed-source or open-source), you are not allowed to claim that that specific piece of code is yours. That being said, MIT is vague about giving attribution.
    – haylem
    Nov 23, 2015 at 18:41
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    @this: The usual (both correct and decent) thing to do is to include, as part of your software, the terms of this license carrying the original author's name and copyright notice, and a note as to what it refers to. Depending on your software's form, this can be either in a LICENSE file, a "About..." dialog, or an information page, as long as it's bundled and visible with your software. (again, IANAL).
    – haylem
    Nov 23, 2015 at 18:43
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The MIT license allows you to

use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software

as long as the license text (copyright notice and disclaimer)

shall be included in all copies or substantial portions of the Software.

Where does this license text have to appear?

This text should appear where the software is used or copies are made. For example, you should keep the license text publicly visible in any JavaScript, or left as a comment in any PHP files. This is enough, even if the comment in the PHP file isn't publicly visible, because:

If I use MIT-licensed software server-side, do I have to display the copyright notice or disclaimer?

Having MIT-licensed software work server-side (e.g. as a PHP script) to produce a HTML page is not redistributing the software, unless the program includes itself in its output.

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    But who checks if on your server you have license text?
    – Manchineel
    May 11, 2018 at 15:11
  • Usually you're installing them via package manager, hence all files in the package are available. That should be sufficient.
    – acme
    Jul 4 at 13:57
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The full text of the MIT License can be found here.

I'm not a lawyer, but it seems like you can

deal in the Software without restriction

even so far as

distribute, sublicense, and/or sell copies of the Software

provided that

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

Again, I'm not a lawyer, but you might fulfill that condition via comments in all pages or scripts that use the MIT licensed plugin or an Acknowledgments page.

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Every opensource licence to date (MIT too, a BSD-spirited licence) allows you to use the software on a commercial web site (and that's part of the reasons for the extreme OSS propagation in latter years) with some notable exception. Those exceptions are:

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    I don't think we can describe MIT/X11 as BSD-spirited: it's even less restrictive than BSD. They did appear at the same time and are both fairly permissive, though.
    – haylem
    Aug 24, 2011 at 18:05
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    Might be worth mentioning that the point of the AGPL is to fix this particular loop-hole that allows the use of GPL-ed code in a closed-source service provider setting; which is exactly against what the GPL intended: being viral and forcing you to disclose your source if you use GPL code. (might be a bit off on that, never been quite on top of GPL-intricacies).
    – haylem
    Aug 24, 2011 at 18:12

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