For every commit to WordPress coreCore Core is the set of software required to run WordPress. The Core Development Team builds WordPress., as well as for every pull request (PR) on GitHubGitHub GitHub is a website that offers online implementation of git repositories that can easily be shared, copied and modified by other developers. Public repositories are free to host, private repositories require a paid subscription. GitHub introduced the concept of the ‘pull request’ where code changes done in branches by contributors can be reviewed and discussed before being merged be the repository owner. https://github.com/, a suite of performance tests gathers important metrics such as Server-Timing values and Web Vitals. This way, potential performance regressions can be spotted early and reliably.
These tests build the current version/commit of WordPress and open a site with test data in an actual browser, performing multiple requests to gather median numbers. The tests cover multiple different combinations with different themes, MultisiteMultisite Multisite is a WordPress feature which allows users to create a network of sites on a single WordPress installation. Available since WordPress version 3.0, Multisite is a continuation of WPMU or WordPress Multiuser project. WordPress MultiUser project was discontinued and its features were included into WordPress core.https://codex.wordpress.org/Create_A_Network., and object cache setup.
GitHub Actions summaries
For every PR and trunk commit, the performance tests run on GitHub Actions in the WordPress/wordpress-develop repository. Results can be viewed either through Actions -> Performance Tests, or by clicking on the “Checks” tab when reviewing a PR. There, a detailed summary with before, after, and delta is printed for easy analysis.


Note: Due to the nature of how GitHub Actions work, some variance in the results is expected.
Performance dashboard
Commits to trunk are additionally uploaded to a custom-built dashboard at codevitals.run and stored for later use. There, one can observe performance trends over the last few hundreds commit, which makes it easy to quickly spot any big shifts or regressions and narrowing down the potential cause.

Note: spikes can often also be attributed to changes in test methodology, in which case these will be discussed on SlackSlack Slack is a Collaborative Group Chat Platform https://slack.com/. The WordPress community has its own Slack Channel at https://make.wordpress.org/chat/. and in TracTrac Trac is the place where contributors create issues for bugs or feature requests much like GitHub.https://core.trac.wordpress.org/. tickets beforehand and can be anticipated.