How do people qualitatively measure their developer experience?

But also not directly to developer's experience. Try the SPACE framework [1] from the same people, Nicole Forsgren et al. It is more of a survey than measurable objective metrics, and the problem is with the implementation, like any other survey- build good questions, operating the survey analysis and results etc.

There some comercial tools available, for example getdx [2]

[1] https://queue.acm.org/detail.cfm?id=3454124 [2] https://getdx.com/