Many online casino games, from online slots to digital card tables, rely on random outcomes to deliver a fair playing experience. But how are these random numbers actually produced when everything happens on a computer?
It is important for players to trust that each spin or deal is unpredictable and not influenced by the casino or by anyone else. Understanding how random number generation works is a key part of this.
This blog post explores the systems and technology behind online game randomness. It covers what a random number generator is, the role of pseudorandom number generators in online casinos, how these algorithms work in practice, whether hardware-based systems are used, how fairness is audited, and what players can realistically check for themselves.
Read on to learn more.
What Is A Random Number Generator?
A random number generator, often called an RNG, is a computer programme or device that produces a series of numbers with no predictable pattern. This system is used by online casinos to decide the outcomes of digital games, such as which symbols appear on a slot reel or which card is dealt next.
The main purpose of an RNG is to ensure that every game round is independent, and that each result is as unpredictable as possible. This keeps the experience fair because neither the casino nor any player can predict or influence the result.
There are different types of RNGs. In online casinos, the most common approach is software-based and is explained in the next section.
Pseudorandom Number Generators Used By Online Casinos
Online casinos typically use a system known as a pseudorandom number generator, or PRNG, to create random-looking results for their games. A PRNG is a computer algorithm that produces long sequences of numbers that appear random, even though they are generated by a defined process.
A PRNG uses an initial starting value known as a seed. This seed, combined with the algorithm, determines the sequence of numbers produced. High-quality PRNGs are designed so that, without knowing the current seed and internal state, it is not practical to predict future numbers.
The process happens extremely quickly, producing new numbers every millisecond. These numbers are then mapped to in-game outcomes, like which symbols appear on a slot or which card is dealt. PRNGs are widely used because they are efficient, consistent, and simple to integrate into software without additional devices.
How Do PRNG Algorithms Produce Game Outcomes?
Pseudorandom number generator algorithms take a seed and run it through a mathematical formula to produce a stream of numbers. This process is handled by the game software and continues constantly in the background.
When a player initiates a round, the game reads the most recent PRNG number and maps it to a specific outcome. For example, a range of values might correspond to particular slot symbols, a dealt card, or a roulette wheel position. The mapping rules are built into the game and reflect its design, including the return to player and frequency of different results.
Each outcome is produced independently of the others. Previous results do not change what comes next, and the software does not adjust future outcomes in response to a player’s wins or losses.
This software-led approach raises a natural question: are physical, hardware-based randomness sources used online at all?
Are Hardware Random Number Generators Used Online?
Most online casinos rely on software-driven PRNGs for their games. Hardware random number generators, or HRNGs, use physical processes such as electronic noise to create numbers that are not derived from a formula. These devices are valuable in areas like cryptography where unpredictability must be sourced from the physical world.
For online casino games, PRNGs are usually preferred because they are reliable, fast, and easy to integrate across thousands of game rounds without specialised equipment. HRNGs are sometimes used in land-based gaming machines, but are far less common in purely digital casino platforms.
Understanding this distinction helps explain how different games use RNGs in practice.
RNGs In Slots, Roulette And Card Games
Random number generators are central to how online slots, roulette, and card games operate. Each type of game applies RNG outputs in its own way to keep outcomes independent and unpredictable.
In online slots, the RNG quickly generates numbers that correspond to the symbols displayed on the reels. When the spin is triggered, the latest number decides the symbol positions for that round, and the reels then animate to reveal what has already been determined.
For online roulette, RNGs produce a number that matches a single position on the virtual wheel. This number determines where the ball appears to land, mirroring the variability of a physical wheel within a software environment.
In digital card games like online blackjack or poker, the RNG is used to shuffle a virtual deck and choose which card appears next. Each hand or round is separate, so sequences do not repeat in a way that would allow pattern-spotting.
These systems are designed so that neither the player nor the casino can predict or alter the results. That design is then checked through formal auditing.
How Do Regulators And Independent Labs Audit RNGs?
Regulators such as the UK Gambling Commission require online casinos to use RNGs that meet strict fairness standards. To confirm this, accredited independent testing labs audit the systems before launch and at intervals afterwards.
Testing involves several layers. Labs run large-scale simulations, often comprising millions of game rounds, to ensure the distribution of outcomes matches the game’s design and does not show bias. They examine the PRNG’s implementation and review how seeds are created and managed, since weak seeding can undermine unpredictability. They also verify that the mapping from PRNG numbers to game outcomes is correct and consistent with the published rules and return-to-player.
Only when a game passes these checks can it be offered under a licence. Audit certificates are typically displayed on the casino site, and regulators can require re-testing if software is updated or concerns are raised.
Can Players Check Or Test Game Randomness?
Most individual players cannot directly test a game’s randomness because the code and PRNG state are not publicly accessible. However, there are practical signs to look for. Reputable sites are licensed by recognised authorities, such as the UK Gambling Commission, and display certification logos from independent testing bodies like eCOGRA or iTech Labs. These marks indicate that the RNG and game implementations have been reviewed as described earlier.
Some casino platforms also publish payout audits or statistics that show overall return-to-player rates. While RTP does not reveal the result of any specific round, it does show whether the game’s long-term behaviour aligns with its stated design.
If something seems off, players can report issues to the casino operator or the licensing authority so that formal investigations can take place. That process is handled by professionals with access to the necessary data and tools.
If you choose to play, keep it affordable and within personal limits. Never spend more than you can comfortably lose, take breaks, and seek support early if gambling starts to affect your well-being or finances. Independent organisations such as GamCare and GambleAware provide free, confidential help.
Understanding how RNGs are built, audited, and presented on reputable sites helps set clear expectations and keeps the experience grounded in how these systems truly work.
**The information provided in this blog is intended for educational purposes and should not be construed as betting advice or a guarantee of success. Always gamble responsibly.