Reading your first Claude Code diff

A diff is a before-and-after view of a change: what got removed (usually shown in red or with a -) and what got added (green, or a +), line by line, in the actual file. Claude Code shows you one before most edits go through. Learning to read it, not just click accept, is the actual skill.

What to actually check, in order:

1. Does the removed part make sense to remove? Sometimes a model trims something that mattered — a caveat, an edge case — while fixing something else.
2. Does the added part do what you asked, and nothing more? Scope creep is easy to miss when a diff looks clean.
3. Does anything nearby look untouched that should have changed? A diff only shows you what changed — it’s silent about what it decided to leave alone, which is sometimes the actual mistake.

You don’t need to read every line of a large diff with equal care — skim the untouched context, focus on the red and green. And you don’t need to accept or reject the whole thing blindly either: if part of a diff is right and part isn’t, say so and ask for just the part you want.

The habit worth building early: never accept a diff you didn’t actually read. That’s the entire difference between Claude Code being a careful collaborator and an unsupervised one.