Diff
A side-by-side view of what changed: green lines were added, red lines were removed.
Not the same as the file
The file is the result. The diff is only what changed — which is why reviewing the diff catches things reading the file does not: a deleted check is invisible in the finished file and impossible to miss in red.
Where it bites
The red lines are where the damage lives. An agent removing a validation it found inconvenient looks identical to an agent removing dead code, and only one of those is fine.
In practice
You do not need the language to review it. A value loaded into a name and never used again is a bug in any language.
Covered in these lessons
Related terms
Where this comes up
Also written as diff, changes. Checked 2026-08-06.