Diff Checker: Compare Two Texts

First it compares lines. Every line of the original is matched with the changed text using Myers' difference algorithm, published in 1986, which finds the smallest set of added and removed lines that turns one text into the other. Lines that appear in both stay unmarked.

Then it compares words. When a removed line and an added line sit in the same place and share a good part of their words, they are shown as one changed line, and only the words that differ are highlighted. So you see that $1,200 became $1,150, instead of a whole new line to read.

The options apply before comparing: ignore capital letters, ignore spaces at the start and end of lines (indentation, trailing spaces), and ignore blank lines. Each side takes up to 100,000 characters. When two texts differ in too many lines to line up one by one, the part that differs is shown as one removed and one added block instead of freezing the page.

Red lines are only in the original, green lines are only in the changed text. A changed line shows both versions, with the words that differ in a darker shade. The numbers are each text's own line numbers, and the three tiles count the lines added, removed and changed.

A paragraph that moved shows as removed in one place and added in another, because the comparison follows the order of the lines. Long runs of unchanged lines fold to three lines of context around each change; press Show all lines to read everything.

Side by side puts the two versions next to each other (on a phone each change stacks the old line above the new one). Inline reads from top to bottom like a printed tracked-changes copy, and Copy as unified diff gives the same result as plain text with - and + at the start of each line.

When a customer sends back a contract or a proposal, compare it with the version you sent before you sign or reply. Look at the numbers first (prices, quantities, discounts, payment terms), then dates and names, then clauses that appeared or disappeared.

The checker compares plain text. For a Word document or a PDF, copy the text out of each file and paste it here. Text copied from a PDF often breaks lines in the middle of a sentence; turn on the ignore options, or clean both texts with the Text Cleaner first so the comparison shows the real edits and not the line breaks.

A diff shows what changed, not whether the change is acceptable. Read each highlighted line in context before you agree to it.

Two transcripts of the same recording, for example before and after an edit, or from two transcription tools, often differ in line breaks, timestamps and speaker labels more than in words. Remove those with the Text Cleaner first, then compare: the diff shows the words that were heard differently.

Meeting notes passed around a team pick up quiet edits. Paste the version from the meeting and the one in the shared document to see what someone changed. For two lists (emails, leads, part numbers), sort both A to Z in the Text Cleaner first; the diff then shows which entries are on one list only.