How is this different from plain duplication?

Plain duplication keeps the copies identical; divergent copies started identical and then changed in only some places. That is the dangerous kind, because a fix applied once silently never reaches the other copy.

Are there cases where divergent copies are fine?

Yes, when the two blocks deliberately implement different behaviors — but then the difference should be visible: distinct names and a comment saying so. The scan only flags divergences that look accidental.

What happens if I fix only one copy?

The finding persists. The scanner still sees two blocks sharing a prefix that disagree, which is exactly the state that caused the drift in the first place.

AI code debt

Divergent Copy Check — Did Copies of the Same Code Drift Apart?

DevMeth checks the 48 known AI-code failure patterns — not a penetration test or a security guarantee.

What the issue is

Two blocks of code that began as one copy no longer agree: they share a clear prefix and then differ. That is how a fix lands in one place and stays out of the other — the same logic now behaves differently depending on where it runs.

Why AI tools generate it

An agent iterating on a problem often copies the working answer and modifies the copy for the next prompt, never updating the original. Each subsequent change to one copy deepens a divergence the agent never notices.

How DevMeth detects it

The scan hashes normalized line windows, groups blocks sharing a 6-line prefix, and flags pairs whose post-prefix tails differ. Blocks that remain identical to the end are routed to the duplication check instead.

What a finding looks like

Critical

Two blocks that started identical have silently drifted apart — one copy changed, the other did not

WHAT WE FOUND

lib/fetch-wrapper-a.ts — same 6-line opening — the fix landed in only one copy

Sample — illustrative and masked exactly as a real report shows it. Run a free scan to see your own results.

The fix, in three steps

Diff each pair, reconcile or deduplicate it, and state any genuinely intentional difference in a comment. Both members of the pair get fixed together — never just one.

Run a free scan and each finding carries a paste-ready fix prompt you can act on.

Maintainability findings ship in the Rescue Report — bundled with the Launch Pack or available on its own.

Try a free scan

FAQ

DevMeth checks the 48 known AI-code failure patterns — not a penetration test or a security guarantee. A clear result means each known pattern was checked and found clear or not applicable for your app; it is not a guarantee of security.