How to use it
- Paste the original version on the left and the new version on the right.
- Read the highlighted result: green for added, red for removed.
- Check the summary for line counts and the change in tokens.
Why compare prompts
Prompts get edited constantly, by different people, in chat windows and shared documents. Small changes matter: dropping "only" from "reply only in Malay", or moving an instruction from the top to the bottom, can change how a model behaves. A precise comparison shows exactly what changed, so you can connect a change in behaviour to the edit that caused it.
How the comparison works
The tool lines up the two versions using a longest-common-subsequence match, the same approach as developer tools such as git diff. Unlike a simple line-by-line check, it recognises when a line has been inserted or deleted and does not mark everything after it as changed. Where a line has been edited rather than replaced, the specific words that changed are highlighted inside it.
Worked example
Version one of a customer-support system prompt says: "Answer questions about our properties. Be friendly." Version two says: "Answer questions about our listed properties only. Be friendly and concise. If you do not know, say so and offer to connect a human agent." The comparison highlights "listed", "only", "and concise" and the whole new sentence, and shows that the prompt grew by about 20 tokens. Across 100,000 requests a month, that is two million extra input tokens, a cost you can check with the API cost calculator.
Testing prompt changes properly
- Collect a handful of real inputs, including a few awkward ones.
- Run the old and new prompt on each input with the same model and settings.
- Paste each pair of answers into this tool to see what actually changed in the output.
- Keep the new version only if it improves the cases you care about without breaking others.
Other uses
The comparison works for any text: two versions of a contract clause, an original email and the AI-polished version, or two answers from different models. It runs in your browser, so confidential documents stay on your device.
Questions
Is this better than comparing line by line?
Yes. A plain line-by-line check marks every following line as different after one insertion. This tool aligns matching lines first, then highlights the words that changed within edited lines.
Is there a size limit?
It handles anything up to a few thousand lines comfortably. Very large files may take a moment.
Does it judge which prompt is better?
No. It shows what changed. Whether the change is an improvement depends on testing both versions against real inputs.
Is my text uploaded?
No. The comparison runs entirely in your browser.