Compare, Merge & Diff Files Online
Compare files and find differences online. Edit both sides, jump between changes and merge them left or right — all in your browser.
How to use this tool
Steps for using the Compare, Merge & Diff.
- Paste or type the original text in the left pane and the changed version in the right pane — or use Open file on either side to load a file from your computer.
- Differences are highlighted as you type: amber for changed lines, red for lines only on the left, green for lines only on the right, with the exact changed words shaded darker.
- Use Previous change and Next change (or Alt+↑ / Alt+↓) to jump between differences; both panes scroll together.
- Click Merge to right or Merge to left to copy the selected change across. Repeat until the files match.
- Click a title above a pane to rename it, then Download either side to save the merged result.
Example
Spot what changed in a config file
level: info → level: debug
port: 8080 → port: 8443
(no line) → tls: true3 changes: 2 changed lines, 1 added line
Changed words: info → debug, 8080 → 8443Common use cases
- Reviewing what changed between two versions of a configuration file before deploying it.
- Merging a teammate's edits into your copy of a document or script without a version-control system.
- Comparing exported data, logs or API responses from two environments.
- Checking a generated file against the expected output in a test.
- Reconciling two copies of a file that were edited separately.
How side-by-side comparison and merging work
The tool splits both texts into lines and runs a line diff (the Myers algorithm, the same family of algorithms behind git diff). Runs of lines that differ become changes: a block that was replaced on both sides, a block that exists only on the left (deleted), or one that exists only on the right (inserted). Inside replaced lines a second, word-level diff marks the exact words that changed.
Because one side can have more lines than the other, the panes keep their own line numbers. Scrolling is linked through the diff, so when you scroll past an inserted block on the right the left pane waits at the matching line instead of drifting out of step.
Merging copies one change across: Merge to right replaces the right side's version of the selected block with the left side's lines, and Merge to left does the reverse. The diff is recomputed immediately, so the merged block disappears from the list of changes. Both panes stay editable, so you can also fix things by hand.
Ignore whitespace treats runs of spaces and tabs as equal and ignores leading/trailing space; Ignore case compares letters case-insensitively. These only affect what counts as a difference — merging always copies the exact text.
Limitations
- Comparison is line-based; moved blocks show up as a deletion plus an insertion.
- Text files only, up to 20,000 lines per side. Files are read locally and never uploaded.
- Highlighting is skipped above about 150,000 characters per side to keep typing responsive; the change list and merging still work.
Frequently asked questions
Are my files uploaded?
No. Files you open are read by your browser and compared on your device. Nothing is sent to a server or stored, and downloads are generated locally.
How is this different from the Text Diff Checker?
The Text Diff Checker produces a read-only report and a unified patch. Compare, Merge & Diff keeps both sides editable, links their scrolling, and lets you merge individual changes left or right — useful when you want to end up with one reconciled file.
Can I compare JSON files?
Yes, as text. For a structural comparison that ignores key order and formatting, use JSON Diff.
What do the colours mean?
Amber marks lines that exist on both sides but differ, with changed words shaded darker. Red marks lines only on the left (removed), green marks lines only on the right (added). The selected change has a blue outline.