Diff

You might say

Show me exactly what changed this time—what lines were added and what lines were removed.

See exactly what changed between two statesA diff shows added, removed, and modified lines between the working tree, staged changes, commits, or branches. Read it before committing and reviewing so accidental edits, secrets, and unrelated changes are caught early.

Know first

Git Commit

Before changesButton text− Click me

→

After changesButton text＋ Start now

git diff

Diff is a list of changes: red minus signs indicate deleted content, and green plus signs indicate new content. Read it over before submitting to make sure there are no accidentally deleted, debugged content or keys.

Quick checkChoose the best answer

An Agent says it only changed a button color, but `git status` shows 12 changed files and large deletions. What should happen before commit?

Check only the file count and commit as long as the button file appearsAssume many green additions mean correctness and skip reading removed contentReview unstaged and staged diffs line by line for deletion, debug content, and secrets

You can say this to an AI Agent

Before commit, show unstaged and staged diffs separately, explain each file, and flag anything beyond button color. Check large deletions, debug text, generated files, and real secrets, and wait for scope confirmation.

When to use it

Review work before a commit
$ git diff- <button>Click me</button>+ <button class="btn btn-primary">Get started</button>Red means deleted and green means added; shows changes not yet added
Compare two branches or commits
$ git diff HEAD~1 HEAD 2 files changed, 18 insertions(+), 4 deletions(-)Explicitly compare the two most recent commits
Understand a pull request
📄 index.html+18 −4
- Click me+ Get started
Find an accidental or missing change
AI finished the changes→git diff for a line-by-line review→commit records a revision

When NOT to use it

Review only the filenames and skip the actual lines
$ git add . && git commit -m "AI changes"47 files changed, without reviewing each oneWhen something breaks, it is hard to identify the exact change
Assume a small diff has a small product impact
+ console.log("test 123")+ // debugger;Temporary debugging code was committed tooUse diff to remove debugging code before committing
Include formatting changes that hide the real edit
3 files changedA file list alone cannot confirm the exact line changes
Copy secrets into a diff shared outside the team
- <nav>…entire navigation bar…</nav>- <footer>…</footer>+ <nav>New navigation</nav>The deletion includes the footer; confirm that is intended

Anatomy

      📄 index.html
      @@ -12,5 +12,5 @@
      - <button>Click me</button>
      + <button class="btn btn-primary">Start now</button>
    

Which file does this change belong to? One file and one section.

@@ -12,5 +12,5 @@: Change near line 12

Red with - sign: lines that existed in the old version and deleted in the new version

Green with a + sign: extra lines in the new version

Variants

git diff

Check what has been changed in the workspace relative to the staging area

git diff --staged

Review after add and before commit

git diff commits

git diff HEAD~1 HEAD

Review specific changes from the most recent commit

git diff main..feat

git diff main..feat/dark-mode

Before merging, check how far ahead the branch is

Typical use cases

Pre-commit review

zsh — my-first-page

$ git diff diff --git a/index.html b/index.html @@ -12,5 +12,5 @@ - <button>Click me</button> + <button class="btn btn-primary">Start now</button> The red band - is deleted, the green band + is added

Pull request

zsh — my-first-page

$ git diff HEAD~1 HEAD --stat index.html | 10 ++++++---- style.css | 12 ++++++++++++ 2 files changed, 18 insertions(+), 4 deletions(-) $ git diff HEAD~1 HEAD Check the line-by-line details again to confirm the content of this round of AI modifications

Bug investigation

ConversationCommits 3Checks ✓Files changed 2

📄 index.html +18 −4

@@ -12,5 +12,5 @@
- <button>Click me</button>
+ <button class="btn btn-primary">Start now</button>

Release comparison

🤖 AI finishes a round of changes → 🔍 review git diff line by line → ✅ git commit record

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