Diff Checker
Compare two texts side by side and instantly highlight additions, deletions, and unchanged lines. Powered by an LCS diff algorithm — all in your browser, nothing sent to a server.
How to Use the Diff Checker
Paste your original text into the left panel and the modified version into the right panel. Click Compare to instantly see every line-level difference highlighted in color.
Reading the Results
Green lines with a + prefix are additions — text that exists in the modified version but not the original. Red lines with a − prefix are removals — text deleted from the original. Lines with no prefix are unchanged and identical in both versions. The stats bar above the diff shows the total count for each category.
Tips for SEO Workflows
Use the diff checker when comparing old vs. new page content during a content refresh, reviewing AI-generated rewrites against your original, or auditing robots.txt changes before deployment. The Swap button lets you quickly reverse which text is 'original' and which is 'modified' without re-pasting.
Frequently Asked Questions
What is a diff checker used for?
A diff checker compares two versions of a text and highlights exactly what changed — which lines were added, removed, or stayed the same. It is commonly used by developers reviewing code changes, writers comparing document drafts, and SEOs auditing before-and-after content updates to ensure intended changes were applied correctly.
How can a diff checker help with SEO content updates?
When you update a page for SEO purposes — rewriting meta descriptions, adding keyword variations, refreshing body copy — a diff checker lets you verify that only the intended changes were made. You can paste the old version and new version to confirm additions, deletions, and that no unintended text was removed.
How does the diff algorithm work?
This tool uses a Longest Common Subsequence (LCS) algorithm, the same approach used by Unix diff and Git. It finds the longest sequence of lines shared between both texts, then marks any lines in the original but not in the LCS as removed, and any lines in the modified text but not in the LCS as added.
Can I compare page content before and after a CMS publish?
Yes. Copy the live page content, paste it as the original. Then paste the draft or updated content as the modified text. Click Compare to see every line-level change between the two versions — additions in green, removals in red, unchanged lines in grey.
Is there a size limit on the text I can compare?
No. The tool runs the diff algorithm entirely in your browser — there is no server upload and no file size restriction. Very large documents will compute slightly slower on older devices, but there is no hard cap.
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