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How do Online Casino Random Number Generators Work?

Written by

Melissa Kruger
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If you’ve played in the online casino world for any length of time, you’ll have heard the term “random number generators”, known as RNGs, for short. These are arguably one of the most critical components of any casino because they ensure fairness and, as their name suggests, randomness. Every spin of a slot, deal of a card, or roll of the dice or roulette wheel should be governed by RNGs. While it is possible for some to be rigged or altered, there are measures in place to ensure fairness. We’ll look at some of those below.

What Is a Random Number Generator (RNG)?

A casino game random number generator is effectively an algorithm. It has been created by the software provider behind the game to ensure that every turn is truly random. Whether we’re talking about the symbols that appear on reels in slot machines, the shuffling of cards, the numbers that appear when dice are “rolled” or the pocket a roulette ball lands in – all are governed by random number generators.

The purpose of these algorithms is to ensure randomness on each turn. They aren’t designed to even out gameplay. For instance, if a number hasn’t shown up on the roulette wheel for a while, an RNG won’t guarantee that it does. It will ensure that the number has the same chance of popping up as any of the others, though. This is random gameplay at work.

The primary reason casinos use RNGs is two-fold. Firstly, they ensure that every player has a reasonable chance to win, and that the casino cannot “rig games” to cheat players. Secondly, they guarantee that players cannot cheat casinos by counting cards or using hacks and patches to rig games. Thus far, over the last twenty-five years, RNGs have proven immensely effective at ensuring fair and random gameplay for both sides.

How Does an RNG Work?

The specific nature of the algorithms used to ensure randomness will vary from game to game. Each software provider has its own code, and that code will change based on the game you’re playing. For instance, in blackjack, the RNG algorithm will ensure that the deck is shuffled after every hand, leaving no room for players to count cards. In a slot, the algorithms ensure that a random selection of symbols appears on each reel every time you spin them. 

The specific mechanics behind each type of game will vary, but the outcome remains the same – a random set of events that neither players nor casinos can predict.

Are RNGs Really Fair?

There have been all sorts of experiments to discover if RNGs are truly fair. Most have concluded that 99% of the time – yes, they are. To ensure that a casino is fair, the RNGs found in their games are independently audited and tested by third parties. These include bodies such as eCOGRA, iTech Labs and TST (Technical Systems Testing). Casinos will receive an RNG certificate if their games have RNGs that are up to scratch.

The only time that RNGs can’t be trusted is when the casino offering games is fraudulent. Rogue and blacklisted casinos have been known to tamper with the RNGs, and these effectively pirated games are stacked against the player. You can spot these rather easily, though, as the casino won’t be supporting RNG certificates. Therefore, this isn’t an issue most South Africans have to contend with.

Can You Cheat an RNG?

In theory, a mathematical wizard with expert coding skills and the source code to the random number generator could, in theory, cheat the RNGs in games. Anybody who has worked on those codes, for instance, would have a reasonable shot of doing that. However, for your average nickel-and-dime casino player? Not a chance. 

There has never been a reported case of a player being able to cheat casino RNGs, even with hacks and patches deployed. The algorithms are just too complicated and well-hidden. Of course, this doesn’t mean to say that somebody (perhaps former software developer employees) hasn’t done it. However, if anyone did manage to do so, they wouldn’t be likely to report it. Why give away the secret to free money?

How to Make Sure You’ve Gambling Safely

To ensure that you only wager on fair games and at reputable sites, there are certain steps you can take. Follow these measures to ensure that you’re gambling safely at online casinos:

  • Only play at betting sites that are licensed and regulated.
  • Check that your chosen casino is RNG-certified by independent, third-party auditors like those mentioned above.
  • When playing crypto games, look for the Provably Fair certificate, as this amounts to the crypto version of RNG certificates.
  • Examine the RTP rates of games. Slots, for instance, should have an RTP of at least 95%.
  • Play free-to-play slots to see how a game works and how frequently it pays before you wager real money on it.


RNGs are the result of a compromise between casinos and players. While many players would love to be able to manipulate random number generators in their favour, we would hate it if casinos did it, and vice-versa. Random number generators ensure fairness on all sides (excluding house edge, of course) and have proven reliable for almost thirty years. We don’t see this concept going anywhere.

Melissa Kruger author at PlayCasino

Melissa KrugerVerified

Technical Manager & Copywriter


Melissa brings her love for poker and online casinos to the PlayCasino team, where she’s spent three years as part of our family. She's our go-to gal for crafting informative, engaging content that helps players get the most out of their gaming experiences. When Melissa's not busy crafting awesome content, you can usually find her playing her favourite online slots or checking out the latest gaming trends and technologies.

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