Text Diff Checker

Paste two versions of a file or a block of text and see precisely which lines were added, removed or left alone. The result is a standard unified diff — the same format git diff produces — so it can be read by a person or fed straight to patch.

Useful for working out what changed between two .htaccess files, two php.ini files, or the config that worked and the one that does not.

How it works

Comparing two texts sounds trivial until the lines move. A naive line-by-line comparison of two files that differ only by one inserted line at the top reports every subsequent line as changed, which is useless. What you actually want is the longest common subsequence: the largest set of lines appearing in both versions in the same order. Whatever is not in it was either removed from the first or added to the second, and that produces the minimal, human-sensible edit list.

The output here is unified diff format. Each block of changes is a hunk headed by @@ -start,count +start,count @@, giving the line ranges in the old and new files. Inside a hunk, a leading - marks a removed line, + an added one, and a space an unchanged line kept for context. Three lines of context surround each change, which is what makes a patch applicable even after the file has shifted slightly.

Two options change what counts as a difference. Ignore whitespace collapses runs of spaces and tabs and disregards leading and trailing space, which is how you see past a reindent. Ignore case compares case-insensitively. Both affect only the comparison — the lines shown are the originals.

One difference this tool does report, and most people forget to look for, is line endings. A file saved on Windows ends its lines with CRLF, one saved on Linux with LF alone. The two look identical in an editor and are entirely different bytes — which is why a shell script uploaded from Windows fails with a "bad interpreter" error. If the two sides differ only in that respect, it is called out explicitly below.

Frequently asked questions