Spelling, 49, has been friends with Richards, 51, for years but the former Beverly Hills 90210 star said she couldn't resist taking a look at the x-rated content Richards was offering subscribers.
As curiosity got the better of her, Spelling created a user profile under a fake name and admitted she "couldn't stop" spending money on the paid-for shots of her friend.
Talking to SiriusXM's Jeff Lewis Live, she said: "I've been friends with her for years. I was just kind of fascinated by the whole OnlyFans and — I'm not going to lie — I was like, 'Let me check it out. What does it entail?'
"So I looked at it and of course it shows something like unless you subscribe you can't get it. So of course I subscribed under a fake name."
Spelling admitted that once she started viewing the account, she couldn't turn away from it.
"It's riveting because they're like 'Hey we might show you this in the shower,'" she said. "And I just wanted to see, it's my friend and I'm like, 'Hey, how far is she going?'."
The star found it so fascinating that she ended up spending $400 (£322) in just two days.
She said: "They say, allegedly, if you tip them they get back to you faster. So I was like, 'Hey, love what I'm seeing, would love to see some more.' I ended up, in the course of two days, spending $400. I couldn't stop."
The content obviously left a lasting impression on Spelling, who said of her friend: "God she looks good."
Spelling also spoke about her 14-year-old daughter Stella's recent hospitalisation during the interview, saying that she had suffered an acute type of migraine with symptoms similar to a stroke, but that she was recovering at home.