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About this tool
Compare text versions side-by-side with word-level highlighting, version history, churn analytics and markdown export.
The Text Diff Viewer aligns two versions of a document side by side and highlights the individual words that changed inside each edited line, rather than repainting the whole line. It runs a line-level longest common subsequence to pair the versions up, then a second word-level pass on any line that was replaced, and reports similarity and churn as Dice coefficients over words. It is for writers, editors and reviewers who need to see what moved between two drafts.
Open Text Diff Viewer on AltFTool — it loads instantly in your browser.
Paste your code or data sample into the workspace.
Pick the format, conversion, or analysis you need.
Copy the polished result straight back into your project.
Edited lines show the changed words, so a one-word fix does not look like a rewrite.
Snapshot any draft, then load it back into either side to compare against a later one.
Words added plus removed over total words, so you can say how much of a document really moved.
Similarity is twice the shared word count divided by the total word count of both versions — identical drafts score 100%. Churn is the words added plus the words removed over the same total. They sum to 100%: a comparison at 81.5% similarity has 18.5% churn.
When two paired lines share less than 30% of their words, the tool stops trying to align them and marks the whole line as replaced. Below that threshold, word-level highlighting picks out coincidental matches like 'the' and 'and', which is harder to read than a clean replacement.
No. Saved versions live in the browser tab's memory only, so a reload clears them. That keeps the tool free of any storage of your text — nothing is written to disk, and nothing is sent to a server.
Up to 1,500 lines per version. The alignment builds an LCS table of (m+1)×(n+1) integers, so 1,500 by 1,500 is about 2.25 million cells — the largest that stays instant in a browser tab. For bigger files, compare a section at a time.