Our review of Book of 99 cuts through the marketing and looks at what matters: how it plays and how it pays. Developed by Relax Gaming, Book of 99 arrives with high volatility and 95.08% RTP. If everything lines up, Book of 99 can pay up to 500,000x your bet. You get 10 paylines across 5 reels, all leaning into a book of aesthetic. Here's how it stacks up.
Written by Michael Torres · Last updated: February 2026
This title, Book of 99, is the work of Relax Gaming. Presentation-wise it's themed around book of, and it leans toward high variance at a return-to-player rate of 95.08%. Under the hood you'll find a 5-reel grid running 10 paylines.
The mechanics are what make Book of 99 interesting. Look out for scatter symbols that unlock free spins and extra bonus rounds. The high volatility means patience is rewarded — expect quiet spells broken by bigger hits. All told, it's a solid entry in the Relax Gaming catalogue.
At 95.08%, the RTP is slightly below the industry average of ~96%. While this is typical for many popular slots, players should be aware of the slightly lower theoretical return.
High volatility means longer gaps between wins, but when wins do land, they can be significantly larger. A bigger bankroll and patience are recommended for this type of slot.
About 1 in 3 spins results in a win. This is a moderate hit frequency that balances win frequency with payout size.
Book of 99 features scatter symbols that can trigger free spins rounds. Landing the required number of scatter symbols anywhere on the reels activates the free spins feature, giving you extra chances to win without additional bets. During free spins, special modifiers may apply to boost your winning potential.
3.0 / 5 — Good
Book of 99 by Relax Gaming is a solid offering that delivers good entertainment value. The 95.08% RTP combined with high volatility creates a well-balanced gaming experience.