How are slot machines checked and tested?

Have you ever asked yourself how online slots are tested before they are released? That is done by spelcial testing agencies that do so on behalf of the license providers.

We will go a little deeper into the process of these tests. You’ll see that they are extensively checked for reliability and that the correct RTP is achieved.

Verification of online slots

Before they are launched and made available to the public, all online slots must be tested by independent laboratories. This is to ensure that compliance standards and legal requirements are met.

This means that each slot machine must be certified separately for each regulator (i.e. MGA, UKGC, Gibraltar, Latvia and Spillemyndigheden in Denmark). So in the Netherlands this will also happen in a moment. There are several testing agencies available that can do these tests. The best known are eCOGRA, iTech Labs, TST, GLI and NMi.

Different requirements per country

You are best off if the casino you play at has a license issued by the KSA. As of October 1, 2021, this will be the case. This organization is strict and does not hesitate to revoke licenses or not even provide them.

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What will be watched in Holland

Some parts of the test may be skipped, depending on the “physics” of a particular game. For example, if physical devices are not stimulated in the game, or if no perception is created that the outcome of the game is affected by speed or skill, there is no need to test for such factors.

These are some of the technical and operational standards that have been tested for compliance by the Compliance Office:

  • Slot machines must be implemented fairly and strictly and operate in accordance with published rules and the applicable RTP.
  • If there are game instructions that specify a maximum win, then it must be possible to win this amount from a single game.
  • Casino games should operate at a speed that allows the player to determine the outcome of each cycle of the game. Players may be allowed to speed up the speed of a game if they can still determine the outcome of each cycle.
  • The customer should not be forced to play a game simply by selecting it.
  • A mechanism should be implemented to prevent repeated gambling instructions (e.g., when a customer repeatedly presses play while waiting for a game result to be executed).
  • The functions of all buttons on the website and games should be clearly indicated.
  • The outputs obtained from the use of the RNG must be proven: (a) to be statistically independent. (b) to be evenly distributed over their ranges. (c) pass several recognized statistical tests designed to demonstrate (a) and (b) above and the absence of patterns. (d) be unpredictable without knowledge of the algorithm, its implementation and the current starting value.

A lot of technical language but the bottom line is simply that every slot machine also does what is described in the game description of a slot machine. The provider should never fool or lie to the player.


It is quite a long and difficult process before a slot machine is approved. The road from design to a place in the lobby of an online casino is a long one. There are many requirements that an online slot machine must meet. All slot machines must be tested to ensure that everything is correct. Is the Random Number Generator (RNG) checked and completely random? Is the RTP (Return To Player) specified by the provider correct?

Thankfully, the days of weird unreliable casinos are a bit over. Most casinos are all properly vetted and have reliable licenses. You can play there with confidence. Your money is safe there, you get paid out nicely if you win something and everything is in order. In 2021, the online gambling market in the Netherlands will be legalized and there will be proper authorities that will control the casinos. You can then be completely sure that the casinos with a Dutch license meet all the requirements.