What a line-by-line diff is for
Comparing two versions by eye works for a few lines and fails completely past that. A diff does the tedious part reliably: it aligns the two texts, then shows only what differs, so you can look at four changed lines instead of four hundred identical ones.
The common uses are all variations on the same question. Which setting changed between the working config and the broken one. What the vendor altered in the terms document. Whether two API responses that should be identical actually are.
When two identical-looking files differ
If a diff reports changes on lines that look the same, the difference is invisible characters. Windows line endings against Unix ones will mark every single line as changed. Trailing whitespace marks individual lines. A tab replaced by spaces looks identical in most editors and is a real difference to every tool that reads the file.
Character encoding is the other culprit - a byte-order mark at the start of a file, or a curly quote pasted from a word processor where a straight quote belongs.
Comparing JSON and structured data
A text diff of two JSON documents is only useful if both are formatted the same way. If one is minified, every line differs and the diff tells you nothing. Format both first, and if key order varies between them, sorting keys before comparing removes the noise that is not really a change.
Frequently asked questions
- Is my text uploaded when I compare it?
- No. The comparison runs entirely in your browser, so you can safely diff a production config or an unreleased document.
- Why does every line show as changed?
- Almost always mismatched line endings - one text uses Windows CRLF and the other Unix LF. A byte-order mark or a wholesale indentation change will do the same.
- Can I compare two JSON files?
- Yes, but format both consistently first. Comparing minified JSON against formatted JSON marks everything as different even when the data is identical.
- Is there a size limit?
- No server limit, since nothing is uploaded. Very large texts are bounded only by your browser memory.