Diff Checker

Paste the original and the changed text, or open two files, and press Compare. Removed lines show in red and added lines in green, side by side with line numbers or inline with plus and minus signs, and where a line was edited the words that changed are highlighted inside it. Long unchanged stretches fold away. Ignore spaces, letter case or blank lines to see only real changes, swap the sides, and copy the result as a unified diff for a review or a bug report. The comparison runs in your browser.

How it works

Diff Checker is a web page that does its work on your own device. The file you choose is opened by your browser, changed there and saved from there; it is never sent to a server, so there is no copy of it anywhere to delete, no queue and no waiting for an upload. Most online tools of this kind send your file to their servers and work on it there, and many keep it for a while. This one does not. There is no account, no watermark and no limit on how often you use it, and the result downloads the moment it is ready.

Straight to one job

Text Compare

How the comparison works

The two texts are compared line by line to find the longest run of lines they share in the same order; everything else is a removal or an addition. The method is the one version control tools use, with lines that appear only once in each text matched first so that a moved paragraph does not confuse the result, and a careful comparison inside the gaps. Where a removed line sits opposite an added one, the words that differ are highlighted inside the line, so a changed number or a corrected spelling stands out without reading both lines.

Reading the result

Side by side shows the original on the left and the changed text on the right, with line numbers, red for removed and green for added, and an empty cell where one side has nothing. Inline shows one column with a minus or plus in the margin, which is easier on a phone and matches how code reviews look. Long stretches of unchanged lines are folded away with a note of how many; click it to see everything. The ignore options drop spaces and tabs, letter case or blank lines from the comparison, so reformatted text shows only real changes.

Unified diff

Copy unified diff gives the standard patch format, with @@ headers and plus and minus lines, that developers paste into reviews and bug reports and that patch tools read. It uses three lines of context around each change, the usual default.

What this tool does not do

• It does not compare files other than text: Word documents, PDFs and spreadsheets need their text extracted first (the PDF to Text tool does that for PDFs).
• It does not merge or apply changes; it shows them.
• It does not detect moved blocks as moves; a paragraph moved elsewhere shows as removed in one place and added in another.

What it does

• Line-by-line comparison with the changed words highlighted inside edited lines
• Side by side or inline view, with line numbers
• Ignore spaces and tabs, letter case, or blank lines
• Unchanged stretches folded, click to expand
• Unified diff to copy for reviews and patches
• Open files up to 10 MB, swap sides, Ctrl+Enter to compare
• No upload, no account, no sign-up

Questions

How do I compare two texts for differences?

Paste the original in the left box and the new version in the right and press Compare. Lines that were removed are red, added lines green, and inside an edited line the changed words are highlighted.

Can I compare two files?

Yes. Press Open a file above each box to load a text file, such as .txt, .csv, .json, .html or source code, up to 10 MB. Word and PDF files are not text; extract their text first.

What does Ignore spaces and tabs do?

Runs of spaces and tabs are treated as one space and leading and trailing ones are dropped before comparing, so re-indented code or reflowed text shows only the real changes. Ignore case treats A and a as the same; Ignore blank lines drops added or removed empty lines.

What is a unified diff?

The standard text format for changes, used by patch tools and code reviews: a header for each changed region, lines starting with a minus for removed, plus for added, and three unchanged lines of context around them. Copy unified diff puts it on your clipboard.

Why are some unchanged lines hidden?

Long runs of identical lines are folded to keep the result readable, with a note of how many. Click the note to show them all.

Does it work for code?

Yes. Code is compared like any text, with indentation shown as typed; tick Ignore spaces and tabs to ignore re-indentation. Nothing is syntax-aware, so a moved function shows as removed and added.

Is my text sent anywhere?

No. The comparison runs in your browser on your own device and nothing is stored.

Is it free?

Yes, completely free, with no sign-up.

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