GitHub stars are a 'Like' and 'Follow' button for GitHub repositories. When users star a repository, they get updates in their home feed about project releases.
GitHub star growth is surprisingly linear when graphed, even for projects with underlying exponential growth. Why?
First, why even care? Many open-source projects track stars because they don't have other great metrics about their top of funnel. Developers will be first to tell you that "stars don't matter." And to some degree, they don't. For open core businesses, stars might have a low correlation to actual revenue. But it does seem that stars correlate with project popularity and usage.
Some hypotheses that have yet to be tested:
- Star growth is correlated with the log of usage. For example, React has grown exponentially in the last five years, yet its stars are fairly linear.
- Projects rapidly reach their total addressable developers (TAD) on GitHub and then grow at the underlying rate of developers in a sector or skillset or total developers on GitHub (closer to linear). This would explain linearity across a variety of unrelated projects. Some data supports the TAD hypothesis: JS/frontend projects, on average, seem to get more stars (more JS/frontend developers). Kubernetes stars as a subset of Go stars (if you're interested in Kubernetes, written in Go, you're most likely interested in Go itself).
- The correlation between stars and usage is not causal, but due to some underlying confounding variables.
- There are no network effects on GitHub. The social mechanisms (following/followers) and stars themselves do not help repository discovery. Does GitHub need to build out different discovery features to help match developers with code?
Some other surprising facts
- While star growth does seem to increase with large amounts of traffic (e.g., an important release that's linked elsewhere), the effect of this is fairly inconsequential once a repository reaches scale. For example, React's repository doesn't see abnormal star growth during React conferences.
- GitHub stars do carry some weight – open core companies often market them on their landing page as social proof. So I wouldn't be surprised if some of these companies purchase stars or inflate their star count.