Build Basics / Standard term
Diff
A diff is a line-by-line view of exactly which lines a change added, removed, or altered, so you can review what an edit did before you accept it.
A diff is a line-by-line view of exactly which lines a change added, removed, or altered, so you can review what an edit did before you accept it. It marks each changed line, usually showing removed lines with a minus and added lines with a plus, while unchanged lines stay as context around them. Say you ask a coding assistant to fix a password reset email and it reports "done": the diff shows it changed the email text on one line and quietly altered the link expiration on another. Reading the diff is how you catch the second change before it ships.
Builder example
When you ask an AI assistant to edit your project, its summary can sound complete while the change reaches further than you wanted. A request to fix a to-do app's sort order might also rename a field every other screen depends on. The diff is the evidence: it shows every touched line so you approve a tight, scoped change instead of trusting a confident summary. Ask the agent to keep edits small so each diff stays easy to read.
Common confusion: A diff shows what changed between two versions; it does not judge whether the change is correct or safe. A clean-looking diff can still add a line that breaks a feature, so you read the diff to understand the edit and still run the project to confirm it works.