Definition
Top-3 install share is the share of a tag's combined active installs held by the largest three plugins carrying that tag. It shows how concentrated active installs are within a single WordPress plugin tag, rather than spread evenly across every plugin using it. The figure is calculated separately for each tag that qualifies.
Population and window
Rivale measures top-3 install share across the top 12,500 plugins, broken out by tag. The window is a single date, the last day of the report month. The share reflects standing on that date, not change across the month. The same tag-by-tag approach is used across every issue.
How it is computed
Active installs of the three largest plugins carrying the tag, divided by the active installs of all plugins carrying it. Installs are bucketed by WordPress.org, so the share is read to the nearest percent.
How to read it
WordPress.org buckets install counts rather than reporting an exact figure for each plugin. This share is read to the nearest percent, not as a precise number. Read it beside plugins by install size to see how the whole directory's installs are spread more broadly. Read it beside download change by category for the same tag to connect install concentration with download movement. A high share for a tag says installs sit with a few plugins. A low share says installs are spread more evenly across the plugins carrying that tag.
What it is not
Top-3 install share does not name the plugins that hold the share in a given tag. It is not a measure of downloads or of revenue earned by any plugin. It does not cover tags carried only by plugins outside the top 12,500 plugins. It does not state an exact install count for any single plugin within the share it describes. It is not the same figure as download change by category, which records download movement rather than install concentration. It also does not state the combined install total for the tag, only the largest plugins' share of it.
Related measures
Plugins by install size, Download change by tag, Plugin dependencies