Playing at an online casino should feel secure, especially when it comes to trusting the outcome of every game. That confidence rests on technology called Random Number Generators, or RNGs.
RNGs decide each spin, card, or dice roll in a way that is unpredictable and not open to manipulation. They underpin fair play by ensuring results are generated independently and without outside influence.
This guide explains how RNGs work, how they are tested and certified, what regulators require, and how players can check certification for themselves. It also tackles common myths, looks at security measures, explores how RNGs relate to RTP and volatility, and clarifies how digital RNGs differ from live dealer randomness.
Read on to learn more.
What Is A Random Number Generator (RNG)?
A Random Number Generator, often called an RNG, is a computer programme used by online casinos to produce a stream of numbers that cannot be anticipated.
Those numbers determine in-game events. In online slots, they map to reel positions and symbols. In card games, they define the order of a shuffled deck. The RNG runs constantly in the background, creating thousands of values every second, and the game uses the value produced at the precise moment an action occurs.
Most online casinos use digital systems called pseudo-random number generators (PRNGs). Although PRNGs are based on algorithms, they use complex methods and secure starting points to produce results that are unpredictable for gameplay and suitable for fair outcomes.
Because each result is generated independently and applied instantly, neither the casino nor other players can anticipate or steer what happens next. With that foundation in place, it is easier to see how this translates into specific games.
RNG Mechanics In Online Slots
In online slots, the RNG determines the symbols shown on the reels every time the player presses ‘spin’. At that exact click, the RNG selects numbers that the game software translates into reel stops. The mapping between numbers and reel positions is set by the game’s design, which is created and sealed by the developer before the game goes live.
Each spin stands alone. Previous outcomes do not build momentum or create patterns that influence the next result. Strategies that rely on waiting for a certain sequence do not change the underlying process, because the RNG selects new values each time without reference to what came before.
Before release, the slot’s RNG implementation is verified to ensure the mapping is correct, the results meet statistical expectations, and the game behaves as intended. That independent sign-off is how players know the reels are turning as they should.
As soon as you understand slots, the natural next question is how the wider industry checks that every game’s RNG is up to standard.
How Do Casinos Test And Certify RNGs?
Before an online casino game is offered to players, its RNG must be certified by independent experts. Certification examines the RNG itself, the way it is integrated into the game, and the controls around it. The goal is to confirm that results are unpredictable within the game’s design and that no unintended patterns appear over time.
Independent Testing Bodies
Independent testing bodies review and certify casino software to strict standards. Well-known examples include eCOGRA, iTech Labs, GLI, and BMM Testlabs. They assess the RNG, the distribution of outcomes in the game, and the developer’s security and change-control procedures.
Certification is not a one-off. Reviews are repeated at intervals or when software changes, and auditors may also perform unannounced checks. Only products that meet the required criteria receive and keep their certificates.
Statistical Tests Used By Auditors
Auditors use statistical methods to confirm that the RNG and the game produce results that fit the expected model. Common checks include:
- Frequency tests, which verify that values appear as often as they should over large samples.
- Runs tests, which look at the order of results to see if any unusual clustering occurs.
- Serial correlation tests, which check whether one result is connected to the next when it should not be.
Large datasets are analysed to rule out bias and confirm long-term behaviour matches the game’s specifications. Only systems that pass all relevant checks are certified.
Are RNGs Regulated And Independently Audited?
Yes. Licensing authorities, including the UK Gambling Commission, require operators to use RNGs that are independently tested and to keep current evidence of that testing. Those requirements sit alongside broader rules on transparency, player information, and change management.
Oversight continues after a game goes live. Operators must maintain their technical controls, submit to periodic reviews, and address any issues that arise. If standards are not met, regulators can require remedial action.
If you ever want to dig deeper into a specific game, the next section shows how to verify what sits behind it.
How Can Players Verify Game Randomness?
Players can look for clear signs that a casino’s games use certified RNGs. Most reputable sites display testing seals or certificates in the footer or on a dedicated page. These often name the auditor and the scope of their work, and some link to recent reports.
Licensing details should also be easy to find. A current licence from a recognised authority signals that independent RNG testing and ongoing monitoring are required. Where details feel vague or hidden, that is a reason to pause and investigate further.
If information about a particular title is not obvious, customer support should be able to confirm the game’s certification and testing history.
Common Misconceptions About RNGs
A few persistent myths can muddy the waters. One is the idea of “hot” or “cold” streaks. Because each result is independent, streaks that appear in short runs do not imply a change in the underlying process, and they do not carry over to future outcomes.
Another misconception is that casinos can secretly tilt results within a certified game. In regulated environments, the RNG and its integration are sealed, audited, and monitored. Any change to those components requires a new approval process, which prevents hidden adjustments.
Timing theories are also common, such as playing at night or after a certain sequence. As the RNG produces values continuously and uses the one generated at the exact moment of input, the time of day or the recent history of results has no bearing on what comes next.
With the myths out of the way, it helps to see how the underlying system is secured.
RNG Security: Seed Management And Source Code Protection
Two areas keep RNGs secure: how their starting values are chosen and how their code is protected.
A seed is the starting value the RNG uses to generate its sequence. To prevent prediction, seeds are created using secure methods and kept confidential. Good practice also ensures seeds are refreshed appropriately and handled in a way that avoids reuse or exposure.
Source code protection keeps the RNG’s design and implementation safe. Developers use access controls, code reviews, encryption, and change-management logs to prevent unauthorised changes and to track updates. Auditors examine these controls during certification.
Robust seed handling and code security help ensure the RNG continues to perform as designed, without leaks or tampering.
How RNGs Influence Volatility, RTP And Game Outcomes
RNGs produce the outcomes, but the game’s design sets the shape of those outcomes over time. Two terms explain how this plays out: volatility and RTP.
Volatility describes the pattern of wins. High volatility games are built to deliver fewer, larger payouts, while low volatility games target more frequent, smaller ones. The RNG follows the game’s paytable and reel layout, so what you see reflects how the developer structured the maths.
Return to Player, or RTP, is the game’s long-term payback percentage. If a slot lists an RTP of 96%, it means that over a very large number of spins, about £96 of every £100 wagered is expected to be returned across all players. It does not predict an individual session, because each spin is still decided independently by the RNG.
Understanding these two pieces helps explain why short-term sessions can vary widely even when the long-term figures are clear.
How RNGs Differ From Live Dealer Randomness
RNG-powered games and live dealer tables generate outcomes in different ways. Digital games rely on algorithms that select values at the moment you play, which are then mapped to reels, cards, or other game elements. In live dealer games, physical processes create the result: a real shuffle, a wheel spin, or a dice roll captured on camera.
Both formats are controlled and monitored. Live studios use secure equipment, multiple cameras, and procedures that ensure fair dealing. RNG games go through the technical testing and certification described earlier, with records kept for audits and regulators.
If gambling starts to affect how you feel or manage money, seeking help early matters. GamCare and GambleAware provide free, confidential support and practical tools such as self-exclusion and deposit limits. Playing within personal limits and taking breaks helps keep the experience in perspective.
Whether a game is digital or live, the safeguards around it are designed to keep outcomes fair and transparent, so you can make informed choices.
**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.