How did you know you were ready for a promotion?

Ideally this is not an exercise you do in isolation. You should have a living doc (written down) with your manager about the various expectations at each level, broken down by the axes at Lyft.

Two very rough heuristics for testing seniority:

• Have you earned the trust of the team? One way to gauge this is by seeing who people turn to when they are trying to get unblocked or are looking for feedback.
• Can very senior engineers roughly tell you who you are and what you work on? For example, if a staff or principal engineer can talk about the project you’re leading, and talk about a good decision you’ve made, that’s a really good sign.