Diff Checker: Compare Two Texts

How the comparison works

The texts are compared line by line with the Myers difference algorithm, the same algorithm behind git diff and GNU diff. It finds the shortest list of insertions and deletions that turns one text into the other, which is the same as finding the longest run of lines the two have in common. Lines that were edited show up as a removal followed by an addition; the tool pairs them up and runs a second, finer comparison inside each pair, word by word or character by character, to highlight just the part that changed.

Unchanged stretches are folded away with three lines of context around each change, as in a code review. Click a folded stretch to open it, or turn folding off to see both texts in full. Very large or almost completely different inputs are still compared quickly: past a work limit the tool reports the remaining region as one block of changes instead of searching for the smallest possible diff, and it says so above the result.

Ignoring whitespace, case and blank lines

Ignore whitespace

Lines that differ only in spaces, tabs or indentation count as equal, like git diff -w. Useful after reformatting code or re-wrapping text.

Ignore case

Upper and lower case letters compare as equal, so a heading changed from Title Case to sentence case is not flagged.

Ignore blank lines

Changes that only add or remove empty lines are greyed out and left out of the counts and the patch.

Words or characters

Choose how finely changed lines are highlighted: whole words suit prose, single characters suit code, IDs and numbers.

Side by side or unified view

The side by side view puts the original and the changed text in two columns with their own line numbers, aligned so that a changed line sits next to its new version. It is the easiest view for reading prose and for long lines. The unified view shows one column, with removed lines marked - and added lines marked +, exactly as a patch file or a pull request shows them; it works better on a narrow screen.

The counts above the result give added, removed and changed lines. A changed line is one that was edited in place; a removed line has no counterpart in the new text.

Line numbers on both sides refer to the texts exactly as you pasted them, so you can find each change in your own editor. The arrows above the result step through the changes in order and centre each one; the counter shows which change you are on.

Patch files and other formats

The download is a unified diff: --- and +++ headers naming the two files, then @@ hunks with three lines of context, the format read by git apply, patch -p1 and every code review tool. It marks a missing newline at the end of a file the standard way, so applying the patch to the original reproduces the changed text exactly.

For JSON, a line diff is often the wrong tool: reordered keys or a re-indented file look like changes everywhere. The JSON diff tool compares the structure instead and ignores key order and formatting. To count the words in either version, use the word counter.