Text Diff Checker — Compare Two Texts

How it works

Place the old version on the left and the new version on the right, then compare. The result uses a longest-common-subsequence line comparison. Added lines show +, removed lines show − and unchanged lines show = in the table. Old and new line numbers help locate each change. Downloaded text uses a prefix on each line; it is a readable comparison, not a unified patch file.

Limits and behavior

Windows and old Mac line endings are normalized to line feeds for comparison. Spaces, tabs and a final newline are otherwise significant. Empty text is supported. Repeated lines may have several equally valid alignments. The tool selects one consistent alignment; it does not compare syntax trees or detect moved blocks. Limits are 1,500 lines per side and 1,000,000 line pairs.

Example

Changing const answer = 41; to const answer = 42; produces one removal and one addition. A trailing blank line appears separately. Each input is limited to 200,000 characters.

Assumptions and limitations

Start with Load example to see the expected input shape. Replace the example with your own text and choose the relevant operation. Editing an input invalidates the previous output so an old result cannot be copied as if it were current. Copy and download buttons become available after a successful run. Clear removes the visible inputs and output from the page. Limits keep small development tasks responsive; use a local editor or dedicated command-line utility for very large files. A successful transformation does not validate your application logic or make untrusted data safe to execute.

Sources

Lecture notes · Longest common subsequence

Frequently asked questions