Compare two pieces of text side by side. Works for code or prose.
Spotting the difference between two versions of a document by eye is slow and unreliable — a changed digit in a config value or a reworded sentence in a contract slips past easily. This free diff checker compares two pieces of text side by side and highlights every change: removed content tinted red on the left, additions green on the right, with line numbers on both sides and a summary of how many lines were added, removed, and unchanged.
Three granularities cover different jobs. Line-by-line is the classic code diff, right for source files, configs, and SQL. Word-by-word suits prose, where a whole line lighting up because one word changed is just noise. Character-by-character pinpoints single-character edits in keys, URLs, or serialized data. Two toggles — ignore whitespace and ignore case — let you mute differences you do not care about, like reindented code or inconsistent capitalization.
The comparison runs entirely in your browser, so it is safe to diff things you could not paste into a random website otherwise: contracts, internal configs, API responses containing customer data. Use it to review a copy edit, verify a deployment config change, or check what a vendor quietly altered between two versions of their terms.
Put the older text in the Original box and the newer text in the Modified box. The diff computes instantly as you type or paste.
Select Line by line for code and configs, Word by word for prose, or Character by character to catch single-character edits.
Tick Ignore whitespace to skip indentation and spacing differences, or Ignore case to treat capitalization changes as equal.
Removed text is highlighted on the left and added text on the right, with line numbers for both versions and a summary of lines added, removed, and unchanged.
Yes. Both texts are compared locally in your browser and nothing is uploaded or stored, so it is safe to compare confidential documents, contracts, or configuration files.
A line diff marks whole lines as changed, which suits code. A word diff highlights only the words that differ, which reads better for prose. A character diff is the finest grain and pinpoints individual character changes inside otherwise identical text.
Yes. Line-by-line mode with the Ignore whitespace option works well for code, and the side-by-side line numbers make it easy to locate each change in your editor.
That is how line mode works: any difference marks the full line. Switch the Diff mode to Word by word or Character by character to highlight only the exact part that changed.
There is no hard limit, but because the diff is computed live in your browser, very large inputs of hundreds of thousands of lines may become slow. Typical documents, configs, and source files compare instantly.
ReSlug logs link edits and lets you see what changed and when on Pro plans.