Prompt Diff
Free online prompt diff tool, no installation required. Compare two prompt versions with highlighted changes
About Prompt Diff
Prompt Diff compares two pieces of text line by line using a Longest Common Subsequence (LCS) algorithm and renders a unified diff view with additions highlighted green, removals highlighted red, and unchanged lines left plain. Each version is entered into its own Version A and Version B textarea, and the comparison produces counts of added, removed, and unchanged lines that you can copy as a prefixed diff.
How to Use
1. Paste the original text into the Version A card. 2. Paste the revised text into the Version B card. 3. Click the Compare button to compute the diff. Editing either textarea automatically hides the previous result so a fresh comparison is required. 4. After the result appears, read the added (+) / removed (-) / unchanged (=) counters in the header and click Copy to copy the diff text prefixed with +, -, or a space for each line.
Diff Symbols and Counters
Each result line begins with a prefix symbol: + marks a line present only in Version B (added), - marks a line present only in Version A (removed), and a blank prefix marks a line common to both versions. The header shows three counters: a green +N for added lines, a red -N for removed lines, and a muted =N for unchanged matching lines. When both inputs are identical, the view shows only unchanged lines and the add/remove counters are zero.
▶How does the comparison work?
▶Why did the diff disappear after I edited the text?
▶What format is used when I copy the diff?
▶Is my data sent to a server?
If this tool has been helpful to you, consider buying me a coffee.
Buy me a coffee