Paste two versions of any text — find what changed in seconds with a free online text compare tool.
Side-by-side comparison
Original text (Version A)
Changed text (Version B)
Table of Contents
How the Text Compare Tool Works
In every editor you’ve ever used you’ve encountered this problem: You get a new draft, a new paragraph, or a new commit and you don’t know what has changed. A text compare tool can help that puzzle by dividing the two versions into each line and comparing all the lines one by one. It points to the lines that remained unchanged, the lines that vanished and the lines that came new. What you receive is clear before and after picture — which manual proofreading cannot give you.
The algorithm the tool is based on is a classic one, the longest common subsequence (LCS). It does not read both texts, line by line, but rather lines up the blocks of text that match each other and only reports the blocks where they do not. That’s why if you add a paragraph to the middle of your document, or remove a sentence from the top, the results remain unchanged. The unchanged parts are the same and hold the reader’s attention; the changed parts are different.
Also you receive a percentage of similarity. It is determined by the proportion of lines that remain the same between the two versions compared to the number of lines across the two versions. There are two identical texts that will be 100%, two totally different texts that will be 0% and most actual texts will be somewhere in the middle. It’s a good benchmark: 94% means that the edit was relatively light, while 42% means that you ought to be sending it for a rewrite.
Why Compare Texts Online?
Diff checker tools come in handy in many more situations than people think. Submitted manuscript versions are compared for revisions before they are sent out to writers. Editors use Diff to compare two headlines or marketing variations to determine which one has been edited prior to a split test. Developers copy old andnew config files, regression logs or prompts to figure out what changed. Students double-check their paraphrase with the original text to make sure that they paraphrased the text instead of copying it. Recruiters/HR look at responses and/or updated Job Description. Contract redlines, where there is significant meaning in the words changed, are compared even by lawyers and paralegals.
Since everything you paste is executed within your browser, nothing ever leaves your device. No account to create, no server round trip, no upload. It’s perfect for confidential work: review notes for a salary, unpublished research, proprietary code snippets or anything under a non-disclosure agreement.
Use Cases You Might Not Have Considered
- Prompt engineering: You’ve written a prompt for an AI assistant and made a mistake in wording a phrase. Compare the old andnew prompt to determine the exact changes made at the token level and maintain a changelog of what changed.
- Good hygiene of CSV, config: Two CSV exports can have just one different column. A line-by-line diff will tell you where the header line changed, and what rows were removed or added.
- Legal and compliance redlines: Be sure to note any edits made to the contract between versions, to avoid any “silent edits.”
- Translation QA: Side-by-side comparison of two passes of translation to identify phrases that were reworded rather than the previous, approved translation.
- Learning a codebase: Copy and paste a previous version of a script and the new version, these are literally the changelog that someone forgot to write.
Pro Tips to Get the Most Out of It
When comparing drafts where capitalization has changed for style purposes, but not for meaning, turn on Ignore case. When comparing formatted exports or when you are pasting emails where the formatting is cosmetic (meaning that spacing and line-breaking are not significant), use Ignore whitespace. If the two files use different line ending characters (one from a Windows file, one from a Mac file), copy and paste both of them in a plain-text editor before comparing the lines, or each line will show up as different.
If the document is extremely long, do the comparison section-wise. The results remain legible, and a diff of a section is more readable than a wall of green and red. The context around each changed block should be short — most diff readers are based on the principle that if there is enough unchanged text in a chunk, only the lines on the ends of the chunk are important.
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Common Mistakes and FAQ
Why does the tool display various data when I copy from a PDF?
Invisible soft line breaks, double spaces, and non-breaking spaces are often embedded in PDFs. The two lines are identical in appearance but NOT in content. To compare the text, enable Ignore whitespace or clean the text in a plain-text editor.
If the similarity is 100% but with different formatting, what does that mean?
It indicates that all of the lines will match after you select your options. Changing from Version to version will not be flagged if you ignore case. This is typically what you want in the case of style-only edits but if the case change is meaningful, uncheck and re-run.
Is it limited in size of the text?
This tool compares locally, so it depends on your browser and device for performance. It reacts in real-time for thousands of lines of everyday documents, essays and code files. If the input is large, break up the comparison into smaller segments.
Is there a way to find out whether two texts are the same?
Yes, but diff checking will provide a percentage of similarity instead of a plagiarism verdict. Near 100% are identical or near identical, lower scores are for substantially rewritten text. If you are doing a formal plagiarized check, you should use a dedicated plagiarism service and consult your sources.
Does the tool store my texts?
No, everything is done in JavaScript on your device, and a refresh of the page will clear both panels. No database, no analytics pipeline that sees your content, no server side copy.
Last updated: September ️8, 2026
Disclaimer - This text compare tool is provided for general informational and productivity purposes. Results depend on the input provided and may not suit specialized legal, scholarly, or forensic comparison requirements. Always verify critical differences manually or with professional tooling where accuracy is essential.
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