Diffdeck compares two text files side by side. Matching lines stay lined up, and the words that actually changed are highlighted inside each line.
Everything here exists to answer one question quickly: what is different between these two files?
Both panes scroll together and matching lines sit directly across from each other, so you never lose your place mid-comparison.
When a line was edited rather than added or removed, Diffdeck marks the exact words that changed inside it.
Collapse the untouched stretches of a long file and keep a few lines of context around every edit.
Turn off whitespace-only differences and changes in capitalisation so only real edits remain on screen.
Save a comparison as an HTML report, a standard unified diff patch, or a CSV with one row per changed line.
Comparisons run on your own computer. Nothing is uploaded and no sign-in is ever requested.
Three steps, no setup and no project to configure.
Pick the older version first — notes, Markdown, config, JSON, CSV, logs or source code.
Diffdeck lines the two up automatically and shows the comparison straight away.
Jump between changes, hide the unchanged parts, and save a report if you need to share it.
No. Diffdeck reads both files on your own computer and compares them there. No copy of your file contents is sent over the network, and the app does not require an internet connection to compare files.
No. There is no account, no sign-in and no profile. Diffdeck does not collect a name, an email address or any other personal detail.
Your preferences, and a list of your recent comparisons so you can reopen one quickly. That list records the file names and locations you compared together with the number of changes — never the contents of the files themselves. You can clear it at any time from the recent comparisons window.
Any plain text file: .txt and .md, configuration files, .json, .csv and .xml, log files, and source code in any language. Character encoding and line endings are detected automatically. Binary files are not text, so Diffdeck declines them rather than showing meaningless output.
Files up to 20 MB each can be compared. That is far beyond the size of ordinary documents, configuration files and source files.
Yes. Export an HTML report and it will open in any web browser with the side-by-side layout and highlighting intact. You can also export a standard unified diff patch or a CSV of the changed lines.
English, Simplified Chinese, Traditional Chinese, Japanese, Korean, French, German, Spanish and Italian. Diffdeck follows your system language the first time you open it, and you can change it at any time.
Diffdeck is a one-off purchase on the Microsoft Store. There is no subscription, no advertising and no in-app purchase.