How do I know if my developer is doing a good job?
The most reliable proxy is whether similar work is getting slower over time, and whether a change can be reverted quickly when it turns out to be wrong. Both are measurable without reading code, and both track the health of the system more accurately than code appearance.
From Staying in control of software you can't read, published 9 August 2026. That article is where the reasoning behind this answer is set out, including what it does not cover.