DRY Review

DRY is about knowledge, not text. A finding is the same decision encoded in two or more places that have to change together — so that changing one and forgetting the other is a bug waiting to happen. Two blocks of similar-looking code that encode different decisions are not duplication, and merging them would couple things that should vary independently.

What to look for

• Rules and validation — the same allow-list, regex, limit or permission check in a form, an API endpoint and a CLI command.
• Constants and magic values — a status name, a timeout, a URL, a field name or a path spelled out in several files instead of defined once.
• Parsers and formats — two hand-written parsers or serializers for the same file, header, JSON shape or command output.
• Protocol details — the same auth header, retry policy, pagination loop or error mapping re-implemented per client.
• Copied functions — a helper copied into a second module with small edits, where both copies are still meant to behave the same.
• Docs and code — a procedure described in two documents, or a value documented in a README and hard-coded elsewhere, when both must stay in sync.

In a diff, check first whether the change adds a copy of something that already exists in the codebase: search for the key identifiers, strings and regexes it introduces.

Not a finding

• Similar code that encodes different decisions, or would diverge on the next change.
• Two or three lines of glue, test setup or boilerplate the framework expects.
• Tests that restate expected values on purpose.
• Duplication across separately released projects (a public library and a private monorepo) that are deliberately kept standalone.
• Generated, vendored and lock files.

Severity

• high — the copies have already drifted: they disagree today, and you can show the input that behaves differently in each.
• medium — default: the copies are identical now but must change together, and nothing ties them.
• low — small repeated literals or helpers where a mismatch would be cosmetic.

Reporting a finding

Each finding carries:

• rule — DRY;
• locations — file:line of every copy, not just the one in the diff;
• knowledge — one sentence naming the single decision the copies share;
• cost — what goes wrong when one copy changes and the other does not (or already has);
• fix direction — where the one source of truth should live, preferring an existing module, config or constant over a new abstraction.

Verify each finding by reading all copies side by side before keeping it. Fewer, true findings beat a long list.