Definition
This measure records WordPress plugin support for WordPress versions. It is based on the "tested up to" field that each plugin author declares on their own listing. It shows the share of plugins naming a given WordPress version in that field. The figure is drawn from the directory, not from any outside test. The field can name any WordPress version, not only the newest one.
Population and window
Rivale measures this across the top 12,500 plugins and the whole directory. The whole directory means every plugin listed on WordPress.org on the issue's data date. The window is a single date, the last day of the report month. It is stated together with the number of days passed after the WordPress version was released. An issue may also show new declarations by week within the report month.
How it is computed
Plugins naming the version in the "tested up to" field, divided by the plugins in the population. The field is declared by the plugin author and not verified, so the measure records what an author states, not a test result.
How to read it
The "tested up to" field is set by the plugin author and not verified by WordPress.org or by Rivale. A rise in this figure shows more authors declaring support for a version. It is not a confirmed compatibility test run on the plugin's code. Read it beside PHP requirement to see how the two author-declared fields move together. Read it beside update rate to see whether new declarations track alongside release activity in the same month. The days-passed figure shown beside it gives a sense of how much time authors have had to update the field.
What it is not
This is not a test result. It does not confirm that a plugin actually works correctly on the version named in its "tested up to" field. A plugin left undeclared is not counted as unsupported, only as not yet declared by its author. The field can lag behind a plugin's real compatibility in either direction. It is not a measure of plugin quality or safety, only of a declared field on the listing.