How Are Slot Machines Made?

Online slot games are immensely popular. In fact, slots are probably the most profitable games for online casinos. This is because they are simple to play, and that attracts gamblers. However, many of them also offer some huge prizes. Ever wondered the answer to the question ‘how are slot machines made?’. Let us answer that for you.

How Are Slot Machines Programmed?

The online slots sites found here on offer games made by many different developers. You have big ones such as NetEnt, Playtech and Microgaming, plus many smaller boutique game developers such as Red Tiger, Thunderkick & High 5 Games to name a few.

Once the design of the slot has been completed, the programmers can get to work on it. The thing is, programming a slot is among the hardest type of programming that you can do.

The job of the programmer is to ensure that the slot machine is as random as possible. This means that they will have to program something called a ‘random number generator’. We will talk a little bit more about how that works in the next section when we talk about how slot machines actually work. Of course, it isn’t as simple as the programmers giving random results. They also need to consider:

  • How often the slot machine pays out
  • What the prizes are

The job of the programmer is to ensure that the slot machine pays out regularly, but also ensures that the online casino makes a profit. This means that they need to program in something known as a ‘house edge‘ i.e. the numbers need to be random, but the online casino needs to have a little bit of an edge on each spin (generally between 2-5%)

On top of this, the programmers need to think about any bonus features and consider how this will impact the payout rate, and how their programming needs to work.

Honestly, most of the programming for slot machines will be heavily focused on maths. Everything will be worked out a long time before even a line of code is written. The complexity of programming a slot is why you will often find companies just reskinning their old machines. It is easier like that.

Slots will go through huge amounts of testing and code inspections before they are released to the world. This ensures that they are fair.

How Do Slot Machines Work?

The inner workings of a slot machine are quite complicated, but we are going to try and explain it in the simplest way possible. Remember what we said about the random number generator? Well, that is important to the way a slot machine works.

Each time the slot machine is spun, a random number is generated. The number will then be compared against a list of thousands and thousands of potential symbol combinations and feature combinations. The slot will use this list to determine which symbols will appear on the reels and whether something needs to happen e.g. whether the slot needs to make a payment or activate a feature.

The list of symbols is where the magic happens. At least for the casino. The job of the programmers is to ensure that there are more losing combinations than winning combinations, and they need to ensure that the payouts ensure the online casino can make a profit. It is an incredibly complex job, and we have no doubt that a ton of tinkering with this list will take place until it is ‘just right’.

Of course, the slot will also have features. When a slot feature is activated, different lists of combinations are used. Again, these need to be checked constantly to ensure that they are fair.

If you are playing an online slot in the UK, you don’t really need to worry about how slot machines work. All you need to know is that pressing that spin button will either generate you a win, or it won’t. Everything that happens is completely random.

Can Slot Machines Be Rigged?

You will probably hate us saying this but, yes, slot machines can be rigged. However, don’t worry. you aren’t going to come across one of them.

In order for an online casino to have slot machines on their website, they have to pay a licensing fee to the slot developer. For the most part, this is fine. Casinos are more than happy to pay for the software in order to get it on their website. They make a bit of money. The game developer makes a bit of money.

You must remember that no matter the industry, there will always be people skirting the law. There will be willing to scam people. There are some shady online casinos that will essentially ‘pirate’ the slot machine’s software. They then tap into the source code and manipulate the odds. They can manipulate them to the point where players cannot win.

Thankfully, for British gamblers, this will never be a real issue. We have the UK Gambling Commission to protect us. All casinos that operate in the UK need to be licensed and regulated. No licence? No operation. Once sites are licensed, they have to abide by certain rules. One of these is to clearly state the real odds and to not manipulate games in any way. The sites will be regularly inspected to ensure that these stick to these rules.

If you play at a casino licensed in the UK, big or small, you can 100% guarantee that the slots are not rigged. You can’t guarantee the same with unlicensed casinos. In fact, in those cases, they probably are rigged.


Slot machines are complicated. It takes a lot of skill and years of experience to get ‘right’. Not everybody can program a slot machine, this is why the largest slot vendors in the world are multi-million-pound organisations. Just make sure that you are playing slots in the UK with a licensed casino, and all you really need to know is that whatever happens on the reels is completely fair and 100% random.

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