There’s no single ideal metric for measuring engineering performance but measuring merge request, or pull request, (MR/PR) rate is the best metric to start with.
MR Rate measures impact by tracking how many changes an engineer is able to merge into the production code base. Start by setting a baseline of 20 MRs per month per engineer for early-stage companies. Evaluate all engineers against the baseline metric and avoid comparing engineers to each other. Productive engineers will meet the baseline, unproductive engineers will not.