Compares two blocks of text line by line and highlights what was inserted, removed or changed. It is most useful where a version-control diff is not available — two API responses, a config file before and after a deploy, what you pasted versus what a CMS actually saved.
Format both sides first if they are code or JSON. Otherwise a difference in indentation or line wrapping shows up as a change on every line and buries the one edit you were looking for.
Frequently asked questions
Which comparison mode should I use?
Lines for code and structured text — it produces a familiar unified diff with line numbers. Words for prose, where a line-level diff marks a whole paragraph as changed when one word moved. Characters for short strings where you need to spot a single typo or a stray invisible character.
Why does everything show as changed?
Usually line endings or trailing whitespace. A file saved on Windows uses CRLF and one from Unix uses LF, which makes every line differ invisibly. "Ignore trailing whitespace" is on by default to catch the common case; enable "ignore whitespace differences" for the rest.
Is there a size limit?
No hard cap, but diffing is more expensive than it looks — the underlying algorithm is roughly O(n×d) in the size of the input and the number of differences. Documents of a few thousand lines are comfortable; for anything much larger, a local diff tool will be faster.