Safety checker meaning

There are usually two of them and they behave differently. An input filter reads the prompt and refuses before any compute is spent, which is why a rejection can be instant. An output filter inspects the finished frames and suppresses them, which is why the other kind of rejection arrives after the wait, sometimes as a blank or black result rather than an error.

Filters are classifiers, so they are wrong in both directions. False positives are the common annoyance — anatomical terms in a medical brief, violence in a sports context, a brand name that collides with something else. False negatives exist too, which is why a provider's terms, not the filter, define what you are allowed to publish.

Where a tolerance setting is exposed, it moves a threshold within limits the provider set; it is not an off switch, and the provider's policy still governs regardless of the value.