Free Online Code Diff Checker
Paste two versions of a code snippet to see exactly what changed, rendered as two aligned columns — the way most IDEs and Git diff tools display a code review. It helps engineers review source changes, generated files, and configuration patches without installing a repository diff tool.
Why a side-by-side diff view
A side-by-side layout puts the original and changed line directly next to each other on the same row, which makes it much faster to spot exactly what was edited within a line — a renamed variable, a changed condition, a tweaked string — compared to scanning a single unified list of additions and removals stacked on top of each other. This mirrors how most code editors and Git hosting platforms present a diff, so the output should feel immediately familiar if you've reviewed a pull request before.
How to use this tool
Paste the original version of your code into the left box and the modified version into the right box, then click Compare. Removed lines are highlighted on the left in red, added lines are highlighted on the right in green, and unchanged lines appear plainly on both sides so you have context around each change.
Common use cases
- Reviewing a small code change before committing it, without opening a full Git client
- Comparing a function before and after a refactor to confirm only the intended lines changed
- Checking what changed between two versions of a config file or script pasted from different sources
- Spotting subtle differences between two nearly-identical code snippets from Stack Overflow or an AI assistant
The comparison runs entirely in your browser using a local line-diff algorithm — neither snippet is ever uploaded to a server.
How to use Code Diff Checker for related tasks
Paste the two versions, compare code snippets side by side, and use the changed lines to guide a focused review.
Related tools: Text Compare, JSON Compare.
Frequently asked questions
How is this different from the Text Compare tool?
Text Compare shows a single unified column with +/- markers. This Diff Checker shows the same underlying line diff as two side-by-side columns — the original on the left and the changed version on the right, aligned row by row — which many people find easier to scan for code review, since it mirrors how most IDE and Git diff viewers present changes.
Does this understand code syntax specifically?
No — it's a plain line-by-line text diff, so it works for any programming language or plain text equally well. It doesn't parse or format the code, just compares lines as-is.
What do the colors mean?
Lines highlighted in red on the left were removed, lines highlighted in green on the right were added, and unhighlighted lines appear unchanged on both sides for context.
Is there a size limit?
The diff algorithm is capped at 5,000 lines per side to keep the comparison fast and avoid freezing the browser tab on very large pastes.
Should I use a code diff checker or JSON Compare?
Use the code diff checker for arbitrary source text and JSON Compare when structural object changes matter more than line placement.