A gate is a check that stops a model change when the score drops or a regression appears. It is the difference between an eval that is read and an eval that protects.
About 1 min of reading
Write a gate that blocks one change
Write the bar
Before you run it, say out loud what it will print. Then open the answer.
Run the gate against a failing set
Before you run it, say out loud what it will print. Then open the answer.
Write the override reason
Before you run it, say out loud what it will print. Then open the answer.
Gating the config in a notebook gates the wrong thing. The gate runs against what is deployed, the same way the tests do.
A gate that cannot be overridden is a gate that cannot ship anything urgent. The override is a written reason, not a flag.
The gate refuses a score drop beyond the tolerance, and any regression on a case marked critical.
Model output varies between runs. A tolerance of zero turns normal variation into a failed deploy every time.
Critical means a user would notice. That judgement belongs to a person, and it is written in the case file.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.