How Our Games Are Tested by GLI: A Developer Breakdown

Every time I sit at a slot as a player (which I do, because understanding the player experience is part of my job) I know exactly what had to happen before that game was allowed to go live. I know it because I have been on the studio side of that process with our own games at TopSpin.

GLI tested them and it was not a rubber stamp.

This piece covers what GLI actually does, why it exists, and what it means for you as a player when you see a GLI-certified game. I am writing it from the inside, because most explanations of third-party testing are written by people who have never been through it.

What GLI is and why it exists?

Gaming Laboratories International is one of the oldest and most respected independent testing laboratories in the gambling industry. They were founded in 1989, initially to test slot machines for the Nevada Gaming Control Board, and have since expanded to cover online casino games, sports betting platforms, lottery systems, and iGaming software across more than 475 jurisdictions worldwide.

The key word is independent. GLI does not work for game studios. They do not work for casinos. They work for regulators, the licensing authorities that determine whether a game is legally permitted to be offered to players. When the UK Gambling Commission, the Malta Gaming Authority, or any other serious regulator requires that games be certified before they go live, GLI is one of the bodies they trust to carry out that certification.

For us at TopSpin, our games are licensed under Sigma Gaming Limited, which holds a Remote Gambling Software licence from the UK Gambling Commission (Licence 40865). That licence requires that our games meet UKGC technical standards. GLI is one of the labs that verifies compliance with those standards. When we submit a game for certification, we are not choosing to do so voluntarily. It is a condition of being allowed to operate.

What happens before submission?

Before a game reaches GLI, it has already been through internal testing at the studio level. At TopSpin, that means the math model (the probability tables, the RTP calculation, the volatility curve) has been reviewed internally. The game has been played through automated simulation runs that generate millions of virtual spins to verify that the actual RTP the game produces matches the designed RTP within an acceptable statistical tolerance.

This internal process is extensive, but it is also inherently compromised. We designed the game. We have an interest in it passing. Internal testing catches genuine errors but it cannot serve as independent verification, which is exactly the function GLI fills.

When we submit to GLI, we hand over the complete technical documentation package. This includes the math model specification, the full source code of the game, the RNG implementation details, and the game rules as they will be displayed to players. We do not get to decide what GLI looks at. They determine the scope of their review.

What GLI actually tests?

The certification process covers several distinct areas. I will go through each one.

The RNG

The random number generator is the engine of any casino game. Everything that appears random to a player (which symbols land, which multiplier fires, whether the scatter triggers) is the output of the RNG. If the RNG is biased, manipulated, or predictable, the game cannot be considered fair.

GLI tests the RNG against international standards, primarily the requirements set by the relevant regulator for the jurisdiction the game is being certified for. For UKGC compliance, the applicable standards are rigorous. GLI runs a battery of statistical tests on the RNG output (chi-square tests, serial correlation tests, runs tests, and others) to verify that the output is genuinely random and free from patterns that would allow prediction or manipulation.

They also verify that the RNG cannot be influenced externally. A properly implemented RNG generates its output independently of any network state, player behaviour, or casino-side input. GLI checks the implementation to confirm this independence.

For our games at TopSpin, the RNG passed. But it is not a trivial test. The documentation requirements alone for RNG certification run to dozens of pages.

The math model

GLI verifies that the game’s actual mathematical behaviour matches what the studio claims. They take the math model specification (the document that defines symbol frequencies, pay table values, bonus trigger probabilities, and RTP) and they verify it through independent simulation.

Their simulation team runs the game’s math independently of the studio’s own simulation, generating outcome distributions across millions of spins. If our claimed RTP is 96.5% and their simulation produces 96.5% within the certified tolerance band, the math model passes. If their simulation produces 94% because we miscalculated symbol weights, it fails.

This is the test that catches the difference between what a studio intends and what the game actually delivers. Errors in math model implementation are more common than the industry likes to admit. They are almost never malicious, they are engineering mistakes. GLI exists precisely to catch them before they reach players.

The pay table and game rules

Every game must display accurate rules to players. The pay table (which combinations pay what) must exactly match the underlying math. The game rules must correctly describe every feature, every trigger condition, every edge case.

GLI verifies this by playing the game against its rules documentation. They trigger bonus rounds, test edge cases, verify that the scatter pay logic matches the documented logic, and confirm that the multiplier accumulation works as described. Any discrepancy between documented behaviour and actual behaviour is a failure.

For games with complex features (tumble mechanics, carry-through multipliers, retrigger logic) this part of the review is time-consuming. Our crash game submission took longer at this stage than the RNG stage, because the documented edge cases for a crash game are more complex than for a standard online slot.

Return to player verification

The certified RTP is the number that appears in the game information panel, for example, 96.5% for Gates of Olympus. GLI verifies this number is accurate and that the game will produce it over a statistically sufficient sample of play.

The tolerance band matters here. A game certified at 96.5% RTP is not expected to produce exactly 96.5% on every session or even every thousand sessions. RTP is a long-run statistical property. GLI verifies that the game’s math will converge to the stated RTP over millions of spins, and that it cannot be deliberately structured to pay well during the certification simulation but differently during live operation.

This last point is worth dwelling on. GLI’s certification is not just a one-time snapshot. The certification is tied to a specific version of the game code. If a studio modifies the game after certification (changing symbol weights, adjusting pay table values, altering the RNG implementation) the game requires recertification. A certified game that is subsequently altered without recertification is in breach of the operator’s licence conditions.

At TopSpin, version control for certified builds is treated as a compliance function, not just a development function. The certified build is locked. Changes go through a change management process that determines whether they trigger a recertification requirement.

What does a certification failure look like?

We have not had a certification failure on any live TopSpin title. But I have been through rounds of remediation, where GLI identifies an issue during the review process and we have to address it before the certification can be granted.

The most common issues at the pre-certification stage are documentation gaps, not math errors. GLI requires a specific format and level of detail for the technical documentation package. A submission that is technically sound but inadequately documented comes back with a request for additional information. This extends the timeline but it is not a failure, it is the process working correctly.

Actual math failures (where the simulated RTP diverges from the claimed RTP, or where the RNG tests produce non-random output) are rarer but they do happen across the industry. When they happen, the game does not go live and the studio must fix this issue and submit.

What does GLI certification mean when you are choosing where to play?

When you see that a game carries GLI certification, it means a specific set of things have been independently verified:

The RNG producing the game’s outcomes is statistically random and cannot be predicted or externally influenced. The game’s actual mathematical behaviour matches its documented behaviour. The RTP stated in the game information is accurate to within the certified tolerance. The pay table and game rules you can read are an accurate description of how the game operates.

What it does not mean: that you will win. RTP is a long-run statistical property. A 96.5% RTP game will take 3.5% of all money wagered over millions of spins. In any individual session, you can win significantly more than you deposit or lose everything. GLI certification governs fairness, not outcomes.

The distinction matters. A certified game is not a game that pays well. It is a game that pays at the rate it claims to pay, with outcomes determined by a genuinely random process. Whether that rate is good enough to play at is a separate question that involves RTP comparison, volatility assessment, and session bankroll management. I cover these topics elsewhere on this site.

How to verify certification yourself?

Every GLI-certified game should have a certification mark accessible from within the game interface. This is usually in the game information panel or the footer of the game window. Clicking or tapping this should display the certification details, including the certifying body, the jurisdiction the certification covers, and the certificate number.

If a game does not display this information, or if the certification link does not resolve to a verifiable certificate, treat that as a red flag. Legitimate certified games do not hide their certification.

For the games on this site, all titles we recommend are either GLI-certified or certified by an equivalent accredited laboratory. eCOGRA, BMM Testlabs, and iTech Labs are the other major bodies you will encounter. Any of these from a reputable lab under a credible regulator’s oversight carries the same meaning: an independent third party has tested this game and found it meets the technical standards required for fair play.

Conclusion

GLI is an independent testing laboratory that certifies casino games before they are allowed to go live. They test the RNG for genuine randomness, verify the math model matches the studio’s claims, confirm the pay table and rules are accurate, and certify the stated RTP. At TopSpin, our games go through this process because our UKGC-framework licence requires it. A GLI-certified game is not guaranteed to pay you well in any given session but it is guaranteed to pay at the rate it claims, with outcomes no one can predict or manipulate.

That is the minimum standard any game you play should meet. Check for the certification before you play.

Ankur Gupta is the Founder and CEO of TopSpin Games, a regulated B2B iGaming studio licensed under Sigma Gaming Limited (UKGC Licence 40865). He has spent decades building games at the intersection of technology and entertainment and represents TopSpin at major iGaming conferences including ICE Barcelona and SBC Summit.