Book of 99: a classic book slot with a famously high RTP
Book of 99 is Relax Gaming taking the much-loved book slot format and pairing it with one of the most generous default return figures on the market. The name is a nod to its headline RTP, which is why it draws players who want the familiar expanding-symbol free spins round at a friendlier long-run rate. In our testing it is a refreshingly straightforward game by Relax standards, a clean classic rather than a feature monster, and that simplicity is exactly its appeal.
The theme and presentation
The setting is an ancient world of myth and discovery, in keeping with the long tradition of book slots, drawn in a warm, classical style. The presentation is clean and uncluttered, with no attempt to overwhelm you with mechanics or effects. It is a deliberately traditional look that suits a game aimed at players who want the timeless book format done well rather than reinvented.
The mechanics
Book of 99 follows the classic book template. A special book symbol acts as both wild and scatter, and landing enough of them triggers the free spins round. The base game is simple, with standard line wins building toward the bonus rather than layering on extra systems. This is a slot that wins on clarity, not complexity. As with any slot, there is no skill once you commit a spin, so your stake size and your decision to stop are the only controls that genuinely matter, even on a game with a higher return than most.
RTP and volatility
Book of 99 is best known for its default RTP of around 99%, one of the highest published figures for a mainstream slot, paired with a high volatility rating. That high return does not guarantee wins, it simply means the game keeps less over the very long run, and operators can still stock lower RTP versions, so always confirm the figure in the info screen. Our RTP guide explains exactly what that number does and does not promise. The variance remains high, so quiet stretches are still normal. If swings like this are new, our volatility guide is worth a read.
The bonus features
The free spins round is the heart of Book of 99, true to the book format. Triggered by landing enough book symbols, the bonus awards a set of free spins with a special expanding symbol that can cover a whole reel and pay across positions. A strong expanding symbol can deliver the game's best wins, while a quiet round ends modestly. There is no respin gimmick or feature buy in every version, keeping the game close to the classic template. Our bonus guide explains how free spins maths works and why the round will not arrive on any schedule.
How to play Book of 99
To play Book of 99 sensibly, choose a stake small enough that a cold run cannot end your session, and set a loss limit before the first spin. The high RTP is a genuine plus over the long run, but it does not change the fact that the game is high variance, so a firm budget still matters in any single session. Use the demo if your casino offers one so you can feel the rhythm of the expanding symbol before risking money. The free spins are the goal, but they will not come on demand. Licensed casinos for the game sit in our reviews.
Is Book of 99 worth playing?
Strengths: a standout default RTP, a clean classic format and an accessible, uncluttered design. Weaknesses: high variance despite the high return, and a simple feature set that feature hunters may find plain. For players who love the book format and want it at one of the best long-run rates available, Book of 99 is an easy recommendation. Play it for the experience, never as income, and only at a licensed casino. For more from the studio, read our Relax Gaming review, and if play stops being fun, visit responsible gambling. 18+.
Book of 99 FAQ
Why is Book of 99 called Book of 99?
The name refers to its headline RTP of around 99%, one of the highest published figures for a mainstream slot. A high RTP means the game keeps less over the long run, but it does not guarantee wins in any session.
Is Book of 99 high volatility?
Yes. Despite the high RTP, Book of 99 is rated high volatility, so quiet runs are normal and the biggest wins land infrequently. Use small stakes, set a firm budget and only stake money you can afford to lose. 18+.
Where can I play Book of 99?
Book of 99 is available at many licensed casinos that carry Relax Gaming. Choose a regulated operator from our reviews, confirm the RTP in the paytable, and try the demo before staking real money.