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Example: A programmer produces a library. They release that library under the LGPL and provide full source code.

The programmer wants to monetize their product as well.

Rather than offering a "pro" or "plus" version with extra features, the author writes a statement stating: "The LGPL licensed library is free for any use up to 100 operations per hour. If you need to use the library to do more than 100 operations per hour. please purchase a license." The author then offers a paid license that "allows" you to use the library for unlimited operations. They do this under the claim of a dual-license model. The author naturally knows some people will just bypass the limit, but expects that nobody in a serious business or commercial context would "violate" his license and would thus pay the fee.

These operations do not depend on any external server. There is no other technical enforcement of the limitation, other than that the LGPL code does a simple shifting counter to enforce a per-hour limit. But since the code is open source any developer could easily edit out that check.

Is this type of licensing compatible with LGPL licensing? I.e. if a commercial developer did just modify the library to remove that check, and then used the library beyond this 100-operation limit, would you be liable from a licensing standpoint?

If trademark or naming were the issue, suppose you just cloned the code, removed the check, rebranded the project and re-released it yourself under the LGPL with no limitations. Would this be a violation?

Put more succinctly: Can the author of an LGPL library prescribe written limitations on how the library is used, and legally, enforcibly demand payment for the same library with the only difference being you have the "right" to use that library in some other way?

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    As the author you can place whatever restrictions you want on the license, but what you describe could not be called GPL or LGPL anymore. – Brandin Sep 10 at 6:09
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    @Brandin indeed (upvote from me). Nor could it then be called free or open-source software, within the definitions of this site. – MadHatter supports Monica Sep 10 at 7:52
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There are attempts to do this in practice, and they can be quite a mess; see Is Geogebra's "non-commercial only GPL3" license valid?

The GPLv3 (which contains the base requirements for the LGPLv3) has relevant language in section 7:

If the Program as you received it... contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term.

This would appear to allows users to eliminate your sidecar restriction on number of operations when that restriction is placed alongside the (L)GPL.

However, since you are the author chosing a license yourself, you could write your own license which internally limits its applicability to 100 operations. You may use the GPL text as a basis for your license if you change the name and drop the preamble, though your intent about limiting operations is so different from what the GPL allows, I would exercise great care (and seek professional legal advice) about how to create legally valid terms. Such a license will be non-free and GPL-incompatible.

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