Paste two prompts
A is the baseline — the prompt you use today, the one you know works. B is the candidate — the edited version you are thinking of switching to.
See what moved
The diff shows every word added or removed, and the summary says what kind of change each one is: a new rule, a dropped example, a tone shift, a length limit.
Test it, don't guess
Add a few inputs that have caused trouble before, write the rules the answer must follow, and run both prompts against a real model. Promptwatch tells you if B broke anything A got right.
New here? Hit Load example then Run A vs B — demo mode needs no API key and shows the whole loop in about five seconds.
Still not sure what "baseline" and "candidate" mean? Show me an example
Think of it as before and after. Say you run a small assistant that summarises meeting notes, and this is the prompt you've used for months:
Summarise the following meeting notes for the team. Be clear and concise.
Notes: {{input}}Summarise the following meeting notes for the team.
- Keep it under 150 words.
- End with a bulleted list of action items, each with an owner.
- Do not include anything that wasn't in the notes.
Notes: {{input}}Someone complained the summaries were long and missed the action items, so B is the rewrite. Same job, different instructions.
Test inputs would be two or three real sets of meeting notes. Assertions would be rules like max words 150 and contains "action items". Promptwatch runs the same notes through A and B and checks the rules against both answers.
What you're looking for is a surprise. Maybe B now produces action items (two assertions newly passing) — but one set of notes that A handled fine now comes back with an invented owner for a task. That's a regression, and that's what this page exists to catch: before you switch the prompt over, not a week later when someone asks why Dave owns a task Dave never agreed to.
01Prompts
The prompt as it is now — your known-good starting point.
The proposed change — the version you want to check before shipping.
02What changed
Change summary
- Waiting for two prompts.
03Test inputs
The messages, questions or documents your prompt has to handle. Each one is sent to both A and B. Three or four awkward real-world cases beat twenty easy ones.If the prompt contains {{input}} the text is substituted there and sent as a single user message. Otherwise the prompt becomes the system message and the input is the user turn. Leave all inputs blank to run the prompt alone.