In a while, together Plasma 5.3 will be released (independently) a new package: plasma-sdk, containing some very useful tools for development around plasma, some old KDE4 era ones will return, some are new.

• plasmate: lightweight IDE for plasmoids (experimental port to KF5, work in progress)
• plasmoidviewer: useful to test a single plasmoid, in different formfactors (like desktop, panel, and so on)
• plasmaengineexplorer: test and debug tool for dataengines.
• cuttlefish: tool for exploring icon themes
• plasmathemeexplorer: tool used to explore Plasma themes, let’s talk about this one.

Plasma theme explorer is a new tool that is targeted at designers of Plasma themes.
It can open any installed theme and preview it as a grid of thumbnails of the actual elements rendered.
The thumbnails all have a green or a red dot in it. The ones with a green dot mean that the theme directly provides that element, red means the theme doesn’t have it, so it will fallback to the default theme (currently Breeze). So it makes it very easy and fast to assess the completeness of a theme and to decide what elements to do in order to make the theme more complete.

A sidebar on the right will show a bigger preview of the theme element, together a short description of what the element is for, and an edit button (enabled only for themes installed locally in the user home).

Clicking the edit button, will open the SVG of the theme in inkscape, and will run a little sanitizing script on the file after inkscape is closed.
If the theme doesn’t provide the particular element (and we have a red dot in the thumbnail) the corresponding file from Breeze will be copied in your theme folder, and that one will then be opened in inkscape, making the job of completing a theme easier and faster.