Definition
The average time between when a pull request is opened and when a specific reviewer submits their first review for that pull request.
Why it matters
If you’re practicing some form of CI/CD, you’ll want to make sure that work is consistently moving through the software development process. If work consistently gets stuck in the review process, it could be a sign that work is being pushed in large, difficult-to-review increments. Or that your reviewers aren’t well positioned to quickly get to pull requests pending review.
How to use it
When this number is high, it may indicate that reviews are not a high-priority item for reviewers, either because of process or bandwidth issues. Use this as an opportunity to re-evaluate how reviews get assigned and to whom.
FAQ
What's the difference between Review Speed and Time to First Review?
The similarity between these 2 metrics can be confusing! The difference is found by looking at these questions:
How long does it take a specific person to give their first review on a PR?
How long does it take to get to the very first review on a PR?
Review Speed is a metric that's associated with the reviewer. It represents the time between when a pull request is opened and when a specific reviewer first submits feedback.
If I open a PR and you review it 5 hours later, and Dave reviews it 7 hours later,
you would receive a Review Speed of 5 hours, and
Dave would receive a Review Speed of 7 hours for completing that review.
Time to First Review is a metric associated with a pull request, much like Time to Open and Time to Merge. It represents the time between when a pull request is opened and when the PR received its first review.
If I open a PR and you review it 5 hours later, and Dave reviews it 7 hours later, you would see that the Time to First Review for the PR is 5 hours.
The following metaphor can be helpful:
Review Speed is how long it takes my specific delivery person, on average, to deliver a package. Time to First Review is how long it takes packages to be delivered to my house.
Review Speed is an attribute of a reviewer, as it applies to a given contributor or team to describe their review performance. Time to First Review is an attribute of Pull Requests, as it describes how long PRs sit before receiving a review.
To connect to the analogy, the delivery person is the contributor/team, and the package is the PR (Review Speed is the delivery person’s speed, and Time to First Review is the package’s delivery time).