A feature flag goes into the codebase to make a rollout safer. The new behavior lives behind the flag. The team turns the flag on for one customer, then ten, then everyone. The rollout succeeds.
The flag is still in the code.
It is still in the code six months later. Still in the code a year later. The team that added it has rotated. The flag has been "on" for everyone for so long that nobody remembers the old behavior. The branch behind the false value is unreachable in any environment, and yet the code remains, and every reader has to mentally evaluate both branches every time they encounter the flag.
Feature flag debt is the slowest-moving anti-pattern in most codebases. It does no damage on any given day, and it accumulates anyway. Agents make the accumulation worse.
What flag debt costs
