Bus Factor

What is it?

The Bus Factor is a risk metric that answers: "How many team members have to be hit by a bus for the project to stall?"

It estimates the concentration of knowledge in your codebase.

• Bus Factor = 1: Critical Risk. Only one person understands a key part of the system. If they leave, that knowledge is lost.
• Bus Factor = High: Healthy. Knowledge is shared among multiple developers.

How is it calculated?

AST Metrics analyzes the Git history (authorship of lines). 1. It calculates the "ownership" of each file (who wrote the most lines). 2. It aggregates this ownership by Community (not just folders). 3. If a community is 80%+ owned by a single person, the Bus Factor for that community is 1.

How to improve it?

Share Knowledge

If you have a low Bus Factor:

1. Pair Programming: Have the expert pair with others on that component.
2. Code Reviews: Ensure others review changes to critical files.
3. Documentation: Write down the implicit knowledge.