Are commercial plugins allowed?

badbob001 · 02-04-2015, 11:13 AM

I was thinking of asking the developer of a conversion tool to develop a calibre plugin version, but the tool requires a license to be purchased. Are paid plug-ins allowed with Calibre? I looked at the plugin list and while I do see many 'donate' buttons, I don't see anything about 'purchase'.

No, I'm not the developer. But you know how it is when you first start using a new tool, you are super eager to see if the developer can adopt the tool to your workflow... This can only lead to burnout and rage-quit.

eschwartz · 02-04-2015, 11:35 AM

I believe plugin systems by design are excluded from licene terms as separate works, so it should be fine.

So long as the plugin just hooks into certain actions and the commercially licensed code is its own separate stuff, that is (i.e. no importing and using calibre routines as part of its conversion).

What would probably happen (assuming they listen) is they would just create a wrapper around their standalone executables...

BWinmill · 02-04-2015, 11:54 AM

Calibre is licensed under the GPL v3, so they'd have to check with the particulars of the license. I have seen commercial software interface with GPL software before, albeit v2, so it is probably legitimate. The worse case scenario seems to involve open sourcing the plugin component itself, and I think that would only be an issue if they used GPLed code to make the plugin. (In other words, ensure there is a clear separation of the commercial and open sourced components.)

theducks · 02-04-2015, 12:30 PM

You need to check with the Mobilread owner.
I am not sure a 'Buy' button would be allowed here.
Links to a place where you can 'buy' are allowed for books and devices, so that may be allowed if the Calibre Licence terms are not violated

Again ask : Alex Turcic

kovidgoyal · 02-04-2015, 09:20 PM

The plugin code itself would likely have to be made open source, however, the plugin can call any third party closed source utility with no issues, as long as that utility does not in itself use calibre in any way.

You can see the DOC Input calibre plugin for an example of a plugin that calls a closed source third party utility for conversion.

kovidgoyal · 02-04-2015, 09:23 PM

As for actually selling the plugin, that is perfectly fine, as far as calibre's license is concerned.

The only caveat is that the calibre plugin system does not have any support for saleable plugins, so the plugin would have to be sold ont he developers on site as a zip file to be installed manually in calibre, byt using hte "Add plugin from zip file" button.

02-04-2015, 11:13 AM	#1
badbob001 Fanatic Posts: 556 Karma: 1102020 Join Date: Sep 2009 Device: Kindle Keyboard (rip), Kindle Voyage, Fire Tablet 10 '17, iPad '19	Are commercial plugins allowed? I was thinking of asking the developer of a conversion tool to develop a calibre plugin version, but the tool requires a license to be purchased. Are paid plug-ins allowed with Calibre? I looked at the plugin list and while I do see many 'donate' buttons, I don't see anything about 'purchase'. No, I'm not the developer. But you know how it is when you first start using a new tool, you are super eager to see if the developer can adopt the tool to your workflow... This can only lead to burnout and rage-quit.

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02-04-2015, 11:35 AM	#2
eschwartz Ex-Helpdesk Junkie Posts: 19,421 Karma: 85400180 Join Date: Nov 2012 Location: The Beaten Path, USA, Roundworld, This Side of Infinity Device: Kindle Touch fw5.3.7 (Wifi only)	I believe plugin systems by design are excluded from licene terms as separate works, so it should be fine. So long as the plugin just hooks into certain actions and the commercially licensed code is its own separate stuff, that is (i.e. no importing and using calibre routines as part of its conversion). What would probably happen (assuming they listen) is they would just create a wrapper around their standalone executables...

02-04-2015, 11:54 AM	#3
BWinmill Nameless Being	Calibre is licensed under the GPL v3, so they'd have to check with the particulars of the license. I have seen commercial software interface with GPL software before, albeit v2, so it is probably legitimate. The worse case scenario seems to involve open sourcing the plugin component itself, and I think that would only be an issue if they used GPLed code to make the plugin. (In other words, ensure there is a clear separation of the commercial and open sourced components.)

02-04-2015, 12:30 PM	#4
theducks Well trained by Cats Posts: 31,047 Karma: 60358908 Join Date: Aug 2009 Location: The Central Coast of California Device: Kobo Libra2,Kobo Aura2v1, K4NT(Fixed: New Bat.), Galaxy Tab A	You need to check with the Mobilread owner. I am not sure a 'Buy' button would be allowed here. Links to a place where you can 'buy' are allowed for books and devices, so that may be allowed if the Calibre Licence terms are not violated Again ask : Alex Turcic

02-04-2015, 09:20 PM	#5
kovidgoyal creator of calibre Posts: 45,345 Karma: 27182818 Join Date: Oct 2006 Location: Mumbai, India Device: Various	The plugin code itself would likely have to be made open source, however, the plugin can call any third party closed source utility with no issues, as long as that utility does not in itself use calibre in any way. You can see the DOC Input calibre plugin for an example of a plugin that calls a closed source third party utility for conversion.

02-04-2015, 09:23 PM	#6
kovidgoyal creator of calibre Posts: 45,345 Karma: 27182818 Join Date: Oct 2006 Location: Mumbai, India Device: Various	As for actually selling the plugin, that is perfectly fine, as far as calibre's license is concerned. The only caveat is that the calibre plugin system does not have any support for saleable plugins, so the plugin would have to be sold ont he developers on site as a zip file to be installed manually in calibre, byt using hte "Add plugin from zip file" button.

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