domain

Start a DOMAIN.md at the project root with a Language section containing entries: a one-sentence definition plus optional _Avoid_, _Kinds_, _Rules_, and _See_ lines. Create it lazily with the first resolved term rather than scaffolding empty headings.

DOMAIN.md holds what is true about the subject regardless of implementation; decision records hold why a particular setup was chosen. If a statement survives rebuilding everything from scratch, it is domain; if it only makes sense given this arrangement, it is a decision record.

A decision earns a record when it is hard to reverse and involved a real trade-off between alternatives. Surprise is only a prioritization signal, not a third condition; deliberate no-s qualify when they recur or would surprise a reasonable reader.

Yes, the same format applies to records projects, knowledge vaults, and research archives. Entries cover things like fiscal years, members, and banks, and decision records capture filings and structural choices with the same two-condition gate.

Split when the file passes roughly 150 lines and its terms fall into clusters that barely reference each other. Create a DOMAIN-MAP.md at the root and per-area DOMAIN.md files next to the material they describe; length alone is not the trigger.

The domain skill maintains and sharpens an existing model during normal work. domain-adopt is a separate, manually invoked skill that bulk-seeds a model from vocabulary already scattered through CLAUDE.md, READMEs, and other files.