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Principles are the engineering culture every agent inherits. They are config, not control flow: injected into EM, worker, reviewer, and tester contexts, and recorded with the run — but no behavior branches on an individual principle string. Show the active set: 
voss principles show
voss principles show --json
The output lists each merged principle with its source (default or project).

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Defaults

Voss ships with six defaults: 
diff: "Make the smallest diff that solves the task."
evidence: "No factual claim without evidence."
tests: "Tests prove behavior, not coverage theater."
scope: "Do not edit outside assigned scope."
review: "Review intent and correctness before style."
reversibility: "Prefer reversible changes unless the user approves risk."

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Project overrides

Drop a .voss/principles.yml in the repo to extend or adjust the defaults: 
# .voss/principles.yml
diff: "Keep diffs under ~50 lines unless asked"   # replaces the default text
performance: "Measure before optimizing"          # adds a new principle

disable:
  - reversibility                                  # removes a default
Merge rules:
  • A key not in the defaults is added, after the defaults, in project order.
  • A key matching a default replaces its text in place (stable ordering).
  • A default is removed only when explicitly disabled — a null value or a name in disable.
  • Explicit disable wins over redefinition.
A malformed .voss/principles.yml raises a config error rather than silently falling back, so a broken file is never ignored.
Principles can be declared inline in a team{} block as well. Changing principles changes subsequent runs, but historical runs keep the principles that were active when they ran.