How online casino slot software works

We are splitting this article into two parts. In this first part we are going to listen to the casino and then get all technical. In part two we are going to try and get you to visualise how the casino software really works. Having a real practical visualisation should help you to understand things in a way which might help your own strategy.

How online slot casino software works (part 1)

Random Number Generator (RNG)

You may already have heard something about slot machines using random number generators. A quick google search should give you countless results explaining some of the details. But let’s hear one explanation from the horse’s mouth. Here is how one major worldwide casino chain emailed us explaining:

“A very sophisticated Random Number Generator (RNG) determines a randomized outcome of all games.

Whatever the customer bets on has absolutely no influence whatsoever on the result the random number generator arrives at. The systems are completely independent and are extensively tested and fully certified. As all draws are played by many consecutive customers it would be impossible for our system to control the game to our advantage.

The odds for both real money and fun modes (once played online) games are created with this random number generator. In all card-based games, like Blackjack and Baccarat, the decks of cards are shuffled prior to each hand being dealt.
We have customers who lose and at the same time customers who win; this is the nature of gambling.

You can win at the casino games through a combination of skill and luck, however you also need to know when to quit while you’re ahead. All of these variables factor into whether you win or lose at any casino; both online and land based.” ***

random number generator

Par Sheets, probability & player decisions

There is a very detailed and interesting report which will explain a lot of things far better than we can:

This is a very long report (and written about land based slots but the principles remain the same for online slots), we recommend that you at least skim read some of it.

Common complaints

Many players report that a casino websites RNG is fixed in the casinos favour. The casino will always deny this and with so much riding on them playing by the rules we cannot argue with that. They are regulated and tested so that they comply by the rules. There are of course some rogue casinos out there so make sure the casino you choose is certified by a governing body (or check our list of recommended casinos).

Another major complaint against casinos is that the software recognises when you have won a large amount and will try to claw that money back. We have experienced this on many occasions ourselves. On the flip side we have also had a few of massive wins in succession followed by a consistent run of small wins. It is the former examples that we remember however and human brains are easily tricked into seeing patterns and coincidences.

Despite all the data telling us that casinos really are completely random and fair, as a general rule following every big win, we cash our balances out, head to another casino and don’t return to that casino for a while. It is good practice to consolidate your wins anyway and make a fresh start and casino software is so complicated that nobody will really ever know exactly how it works.

There are so many patterns that our brains recognise but we cannot really tell the difference between coincidence and fact. Could the casino software set the entire casino (i.e. every player on every slot) to a losing run? We do not know for sure but having had runs of upwards of 20,000 spins without hitting a decent win, we have learned that sometimes you just have to walk away for a period of time.

After landing a big win, a feature bonus or a free spins win

After landing a big win it is very tempting to exit the slot or take a break. Alternatively after a big win you can be tempted to have a few more spins which can lead into a long sequence of losing spins. We have a simple rule, following any big win, we give the slot 3 spins (at the same bet value) then take a break. The chance of landing a feature can be many hundreds to one so you would expect to virtually never win two consecutive features. However the large amount of times we have landed 2 in 2 spins certainly defies the odds. Of course most times you do not land two big wins in succession and usually you do end up on a losing run so our rule of “3 more spins” is a good rule to live by.

“Skill Stop”

A final little note is about the skill stop when you are one scatter or bonus symbol away from a feature or free spins… there is no skill about it. The result has already been pre-determined before any of the reels have started spinning (as soon as you hit the start button). On some slots you can even see what the outcome will be when the reel in question starts off on it’s “skill stop” spin. Watch the last reel carefully and on a lot of slots it will stop on the same reels as those shown when it set off.


*** We should point out that a losing run on one slot might not be a losing run on another slot. And vice versa with wins. Slot variance and RTP come into play.

Example: The RNG could generate a run of 100 spins with the result between 0.8 and 0.95. These could generate a bad losing streak on a high variance slot. However on a low variance slot the RNG values between 0.8 and 0.95 could all return equal stake up to reasonable wins giving a great winning run. Altenatively RNG results above 0.95 would give reasonable to good wins on a low variance slot but on the high variance slot these can be massive wins.

Worth bearing in mind.


How online slot casino software works (part 2)

We talked a bit about the random number generator (RNG) amongst other things in part 1. Now we are going to try and paint a visual picture of how online slots work which should be far easier to get to grips with.

Please bear in mind that we are talking only about reputable casinos and software platforms. Also bear in mind that the exact details (for example the exact number of possible outcomes for the RNG) can vary slightly from software platform to software platform and how these numbers are generated can vary but the principles we are going to explain hold true for all. We are generalising so that you can get a visual picture of what is going on. We hope this will help you in making your own strategies.

The online slot casino uses a system of two combining pieces of software

Software 1: The Random Number Generator (RNG)

The RNG returns a value between 0.0000000000 and 1.0000000000 for every spin. There are billions of different values the software can randomly generate. And it generates them completely randomly but over a long enough time period the results will show the probability of getting for example 0.1234567890 is the same as the probability of getting 0.9876543210.

The RNG generates hundreds of these numbers every second.

Everyone online at the same casino at the same time is using the same RNG.

Software 2: The individual online slot software

Once you hit the start button on a slot, the slot receives a number from the RNG. The slot then translates this number into either a win or a loss.

What the software also takes into account is the slot “variance”. This is whether the slot is going to pay out more often but lower wins or whether it will pay out far less often but much larger wins. In layman’s terms will there be an average of 100 spins between a ‘big’ win or will there be an average 1000 spins between a ‘very big’ win?

The slot return to player (RTP) is programmed based on one of each of the billions of results being drawn. A highly complicated mathematical formula makes sure the programmed RTP is spot on.

Let’s design our own very basic slot. 1 reel, 1 line, 2 symbols. “Heads” (wins x2 of the stake) and “Tails” (lose stake). We are ignoring variance for this slot as obviously it is as low variance as is possible. The RTP is set to 90%. If the RNG generates a number between 0.0000000000 and 0.4500000000 the slot will translate that into a “heads”. f the RNG generates a number between 0.450000000001 and 1.0000000000 the slot will translate that into a “Tails”.

Never forget though that as with anything random in life, randomness can produce patterns or clumps that don’t cannot be predicted. Flip a coin yourself 100 times and see how strange some sequences will be.

Visualising your online slot casino

Think of playing slots like being a shark. When playing a high variance slot you are swimming in an ocean hunting for food. You can swim for a long time only coming across small fish which do not satisfy your hunger (small wins, less than stake up to 2-5x your stake). You can sometimes swim for miles only seeing a few small fish (consistent losing spins with the odd small win). You can think of the big wins as a dolphin, sea-lion or fishing boats. These are fewer and far between but worth the wait when you get one. Sometimes there are groups of dolphins or sea lions swimming together, sometimes they are alone. Some stretches of ocean are warmer than others and contain larger groups of fish whilst other stretches are cold and low in life-forms.

But always bear in mind that you are not alone in your hunting. Every other slot player online at your casino at the same time is also a shark. So you could be swimming around for some time feeding off the odd little fish thinking there must be a tasty sea-lion around here somewhere, only for another shark to eat it before you get there and without you knowing.

Alternatively sometimes you can be lucky, eat a tasty dolphin and seconds later you come across fishing boat full of juicy humans that have been scared in your direction by another shark.

For low variance slots think of yourself as a shark swimming in a large lake or small sea, where there are more smaller fish clumped together but instead of dolphins and sea-lions there are larger fish (more small wins but the big wins are far smaller).

Keep this visualisation in mind when playing slots as at the very least it should prevent you from chasing your losses too hard or stop you getting greedy and blowing your wins too quickly.

slots fishing