LGTM means “looks good to me”. It is the comment a reviewer leaves to approve a code change, such as a pull request. Four letters, and the code can go to production.
Our shirt shows LGTM in huge letters above a diff of +4,212 −3,987, and the honest truth: reviewed by vibes.
Where LGTM comes from
LGTM is old developer shorthand, and some tools made it official. In Gerrit, the code review tool used by Android and many other projects, the Code-Review label has the values “Looks good to me, approved” (+2) and “Looks good to me, but someone else must approve” (+1).
Google’s engineering practices guide uses “LGTM” as the word for approval. It even allows reviewers to “give LGTM/Approval even though they are also leaving unresolved comments”, when they trust the author to fix them.
Big diffs get less review
The joke works because everybody knows the pattern: a 10-line change gets ten comments, a 4,000-line change gets LGTM. The data agrees.
| Source | Finding |
|---|---|
| SmartBear, code review best practices | Review no more than 200 to 400 lines at a time; “beyond 400 LOC, the ability to find defects diminishes.” |
| Sadowski et al., Modern Code Review: A Case Study at Google | The median change modifies 24 lines. Comments peak at about 12.5 per change near 1,250 lines; larger changes get fewer comments on average. |
Our shirt diff has more than 8,000 changed lines. That is far past the point where reviewers stop commenting.
AI made pull requests bigger
Coding agents write a lot of code very fast, and the review is still done by a person. Armin Ronacher, the creator of Flask, described it in January 2026: “Every day brings more PRs that took someone a minute to generate and take an hour to review.”
A 2026 study by Baltes, Cheong and Treude, “An Endless Stream of AI Slop” analysed 1,154 developer posts and found “review friction” as one of the main themes: AI output burdens reviewers and erodes trust.
How to review an AI-sized pull request
- Ask for smaller changes. One pull request, one purpose.
- Read the tests first. If they do not test the new behaviour, the rest does not matter yet.
- Ask the author to explain the change in their own words. If they cannot, they did not review it either.
- Never write LGTM on a diff you did not open.
If you approve AI code without reading it, you are in the “You’re absolutely right!” loop, but as the human.
Get the shirt
LGTM T-Shirt · 24 €
+4,212 −3,987, reviewed by vibes.
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Who gets paged when the LGTM was wrong.
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FAQ
What does LGTM mean?
“Looks good to me.” A reviewer writes it to approve a code change.
Is LGTM the same as approval?
In most teams, yes. In Gerrit, “Looks good to me, approved” is the +2 vote that allows the change to be submitted.
How many lines should a code review have?
SmartBear recommends 200 to 400 lines at a time, over 60 to 90 minutes. Above that, reviewers find fewer defects.