Reports - Charts and Graphs for Jira Dashboard Free app is the free and limited version of Reports - Charts and Graphs for Jira Dashboard app. Except rate-limiting it has the same set of features. You can reach documentation of the pro app here.
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Free version has a rate limiting of 1 report rendering per 5 seconds. If rate limiting is hit, that is if you try to view 2 reports within the same 5 seconds, one of the latter report will not render.