Really cool stuff. Here's some initial feedback:
"Avoid internal link redirects" -> All the errors I'm getting on my site are due to the login-wall on some of the pages because it's detecting /account/login/?next=... links as internal redirects.
"Use unique titles" / "Set page descriptions" / "Avoid URL parameters" / "Avoid thin content pages" / etc -> Same problem as above with login walls ("Sign in to ..."). I get why, but it's adding a ton of noise. I added /account/login to URLs to ignore but it didn't achieve anything, I'm guessing I must have misunderstood the syntax or it has to be an exact match or some such?
"Avoid inline JavaScript" -> I'm making quite a bit of use of the pattern, which allows me to declare json objects in the body I can later parse in my scripts. This pattern doesn't have all the issues carried with inline js. Can you ignore script tags where the type= is unknown or application/json\?
hsts preload: This is picking up individual pages on the checked site as errors, even though hsts preload really is a domain-wide thing.
"Hide server version data" -> This is picking up "server: cloudflare" as an error. Means no site behind cloudflare will ever pass this which seems overkill.
"Use lowercase URLs" -> So, on my site you can access objects with IDs like youtube's (/id/vZEz7JoNnfgVo...). It's picking up all those as errors. Feels wrong?
UI: Not a fan of the "x inlinks / y outlinks / headers / recrawl / html / copy" links below the URLs on the results page. Low contrast, unclear what I'm clicking and where it's gonna take me. The "copy" button: What am I copying? (Clearly the URL as I tried it, but that'd be more useful as a clipboard button next to the URL for example)
Finally, I ran it on my company's blog and it ended up crawling a ton of the company's various exosites on different domains which wasn't super useful, especially since none of it showed up in the final results.
Hey, this is a really great tool. Fast, slick UI and very clear what it does. I'll keep an eye on it and would love to see what else it can do in the future.
Pricing: It's hard to see myself pay for this; not because it's not worth it (I think it is easily worth a dozen USD / site checked), but because it's so easy to look at what it does and think "Yeah, but, I can probably do all that myself, and if I don't, it's not so important that I need to pay for a tool to tell me what to fix". I think this is the curse of developing products targeted at developers: Devs will tend to think "I can do this myself // I don't need this". In fact, if you hook me up with a free account, I'll use it a bunch ;)
Shoot me an email (see profile) if you want to talk through some more feedback (especially UX feedback). You just provided me with a pretty cool service for free so I feel I have to give back :)