Most tools that show up for "Claude prompt checker" are actually generators in disguise. They rewrite your prompt instead of evaluating it. Here's the six-lever check a real checker uses, with a free in-browser version.
Searching "Claude prompt checker" right now is one of the more dishonest experiences in the AI tools space. You type the word checker meaning "tell me whether the prompt I already wrote is any good." Google hands you back ten generators instead. Tools that ignore your prompt entirely and rewrite it from your topic, with no scoring and no diagnosis. They are not solving the problem you asked them to solve. They are selling you a different product.
This post is the real version. It is the checklist a working marketer (or anyone using Claude seriously) actually runs in their head before sending a prompt. There is a free in-browser tool at the end that automates the scoring, but the framework matters more than the tool, so read the framework first.
"Prompt checker" gets indexed by tools that contain the word checker but do not actually check anything. The product is easier to build (a wrapper around the Claude API that rewrites your prompt) than a real evaluator (which has to define what good means, score against it, and surface diagnoses you can act on).
If the tool you tried did not return a numerical score, did not tell you which dimension was missing, and did not give you a path to fix it, it was a generator, not a checker. You can stop using it. It is not failing you because you used it wrong.
A useful Claude prompt has six structural levers. A bad prompt is missing one or more of them. A "checker" that does not score these six is doing something else entirely. Here they are. You can run the check by hand in two minutes, on any prompt you have written.
Does the prompt tell Claude the exact shape of the output? Columns, word count, sections, format, structure. "Write me a brief" leaves shape undefined, so Claude defaults to the average shape, which is the generic shape.
Does the prompt tell Claude when NOT to answer? Without one, Claude defaults to maximally helpful, which on a question the data cannot support looks like a confident answer to a question that does not have one.
Does the prompt require you to paste actual input in? A prompt that works with no inputs produces generic output by definition. The classic failure: "act as a senior marketer and tell me about Q3 priorities."
{{BRAND_VOICE}} or instructions like "paste the following: brand guidelines, last quarter's report, ICP doc."Is the prompt written like a brief to a colleague, or like a search query? Claude mirrors what you give it. Command-shaped input produces command-shaped output. Terse in, terse out.
Does the prompt ask Claude to mark what is inferred vs. what is grounded in your input? If every claim comes back at the same confidence, you over-trust the output or you have to re-verify every claim by hand.
Does the prompt give Claude permission to tell you the task itself is a bad idea? Prompts written by people who actually use them include a way to push back. Prompts written to look impressive never do.
Here is a prompt I see almost every week. It comes from a junior marketer who has been told to use Claude. It looks reasonable. It scores 1 out of 6.
Lever-by-lever:
Score: 1 out of 6. The output is going to be confident, generic, and useless. The fix is not a different model or a better tool. It is rewriting the prompt to address the five missing levers.
That version specifies the output shape, includes a refuse-condition, requires real source material, reads as a brief, asks for uncertainty flagging, and has a skip condition. Same model, same task. The difference is the prompt.
You do not need a tool to run this check. You can do it on paper. But doing it on paper requires you to remember six things every time, and most people are running the check after they have already mostly written the prompt, when their attention has moved on.
So I built the free prompt audit tool. Paste your prompt, click run, get a score out of 6 with each lever flagged as present or missing. It runs entirely in your browser. Nothing is sent anywhere. There is no email gate. View source if you do not believe me, the detection heuristics are right there in the page.
It is honest about its limits: each lever uses a transparent keyword heuristic to pre-set a hint, and you make the final call. The tool does not pretend to be smarter than you. It is a checklist with memory.
A score of 6 out of 6 does not guarantee a good output. It guarantees that the structural failure modes are not the reason if the output is bad. The remaining ways to fail are: bad inputs (a voice guide that does not represent the voice), wrong task (using Claude for something a calculator would do better), or bad judgment on what to ship (the slop tax: confidently shipping mediocre output because the prompt scored well).
The check is necessary, not sufficient. It tells you whether the prompt itself is sound. The rest is on you, which is the right place for it to be.
Paste any prompt. Get a 0 to 6 score against the six levers above. See exactly which levers are missing. Copy the result text or screenshot the card to share. No email gate. No server. The detection heuristics are visible in the page source.
Open the audit tool