How do you spot spammy/toxic PBN sites? tools or methods?

Moz is a terrible metric to use for anything. I would say majestic + ahrefs + your eyes and brain.

You can go with moz.com for spam score. But I would advise developing your own formula. Try uzing moz spam score combined with Moz DA. Also Check if they registered any traffic with similarweb. A domain with DA above 30 that doesnt show any traffic in similarweb its an indication that the websites DA is articifial (hence PBN related). Also, I would check manually each domain to see of they have any grammar mistakes (rookie move by Pbn-ers).

I tend to just check which domains Google has chosen to index by putting 'site:' followed by the domain into Google. If nothing shows up or what shows up looks spammy it gives me a good enough idea.

Its for a side project - directory of guest posting sites. Decided to aggregate a working list from the link vendors I have worked with. To make life a bit easier, hopefully. Also kind of frustrated with people posing pbns as outreach guest posts. Manually repeating the filter process is a bit of pain, so wanted to know if people here are using any tool or checklists.

Why are you spending that kind of effort? What's your purpose or end game?