RNG certification for slots

What RNG certification for slots means

Every modern slot decides its result with a random number generator: software, or occasionally hardware, that produces a stream of numbers with no usable pattern. When you press spin, the game takes the next number or numbers, converts them into reel positions and pays whatever the paytable says for the symbols that land. RNG certification is a laboratory’s formal confirmation that both halves of that job are sound: the numbers are random, and the conversion is fair.

In Great Britain the requirement comes from RTS 7 of the Remote gambling and software technical standards (opens in a new tab), last updated in its RTS 7 section on 7 May 2024. The Commission’s testing strategy says the randomness of the RNG and its outputs must be analysed by an approved third-party test house before release, and that all new games and RNGs can only go live once the report has been provided to the Commission. Certification is one part of the wider process covered on our page about how slot machines are tested.

The UK rules an RNG must meet: RTS 7 in plain English

RTS 7 has five requirements. Each one closes a different loophole a dishonest or careless game could exploit.

The 7C rule matters for anyone who has felt a near miss was a sign. The Commission’s guidance says a game may not falsely display near misses by substituting one losing outcome for another, and every outcome shown in the rules or artwork must actually be possible. A losing spin that shows two jackpot symbols and a third just off the line must be a genuine result of the reel maths, not a picture chosen to keep you playing.

What a lab checks in a slot RNG

The guidance to RTS 7A lists the qualities an RNG needs. A lab’s job is to show each one holds, using documentation, code review and statistics.

The testing strategy adds detail on method: the lab reviews the RNG documentation, researches known weaknesses of that type of generator, reviews source code to confirm the implementation matches the documentation, and runs statistical testing of the raw output and of the scaled or shuffled data. Labs on the Commission’s list of approved test houses (opens in a new tab) typically use statistical batteries that look for patterns such as values that turn up too often, runs that are too long or too short, and correlation between one number and the next. Passing them does not prove randomness in a philosophical sense; it shows that no detectable pattern exists in very large samples.

Scaling and mapping: where certified slots can still go wrong

An RNG usually produces numbers across a huge range, such as 0 to 4,294,967,295 for a 32-bit generator. A reel strip might have 30 stops. The game has to scale the big number down to a position from 1 to 30, then map that position to a symbol. The Commission defines mapping as the process of selecting an outcome using the result from an RNG, and RTS 7A says any scaling must keep the generator’s qualities.

A worked example of scaling bias

Suppose a lazy programmer divides the 32-bit output by 30 and keeps the remainder. There are 4,294,967,296 possible values. Dividing by 30 gives 143,165,576 full groups with 16 values left over, so 16 of the 30 stops receive one extra value each. Those stops become more likely by roughly one part in 143 million. That is tiny, but it is a real departure from the stated probabilities, and on a large game with many reels and features such errors can add up. Labs test the scaled output, not just the raw generator, precisely to catch this kind of mistake, and they confirm the scaling method keeps every position as likely as the design intends.

The mapping step is where reel strips and weighted reels come in. A design may deliberately give a blank 6 stops and a jackpot symbol 1 stop; that weighting is legitimate as long as it is what the maths documentation says and the paytable is honest about prizes. RTS 7B guidance puts it simply: mapping should follow the prevailing probabilities and pay tables.

What an RNG certificate for slots contains

The Commission’s testing strategy lists what an RNG report should include. Knowing the fields makes it easier to judge a certificate if a casino or supplier publishes one.

• The test house’s details and the test supervisor who signed off the work.
• The licensee’s name, the date of testing and a certificate reference.
• A short description of the RNG and how it is used, including its version number.
• Whether it is a hardware or software RNG, and its digital signature.
• The platform supplier and platform version it was tested on.
• The scope and approach, and a description of every test applied.
• Any limits on use, such as the acceptable degrees of freedom and any dependence on operating-system functions that could affect it if changed.
• The results.

The digital signature ties the certificate to one exact build. If the RNG code or the scaling and mapping changes, the update is classed as major and has to go back to an approved lab. Each game report separately records the game name, its RTP, software number and signature, and the reports are uploaded to the operator’s games register through the Commission’s eServices system.

RNG certification on online slots vs UK gaming machines

The principle is the same in a casino lobby and in a pub, but the rulebooks differ.

A compensated fruit machine still uses random numbers, but it also tracks how much it has paid against what it has taken and nudges future results towards a target. That is why the Commission approves labs separately for compensated games (its gaming machine testing strategy (opens in a new tab) sets who may test which category), and why a pub machine’s behaviour can differ from a fully random online game. Check the machine’s label: our guide to reading a fruit machine label shows where the notice usually sits.

How a slot gets its RNG certified, step by step

1. The supplier documents the RNG: algorithm, seeding, where it runs and how games call it.
2. An approved test house reviews the documentation and researches known weaknesses of that RNG type.
3. The lab reads the source code to confirm the implementation matches the documentation.
4. It collects very large samples of raw output and runs a battery of statistical tests.
5. It repeats the tests on scaled output, such as reel positions for each game that uses the RNG.
6. It issues the report with version, signature and any limits on use, and the licensee uploads it to its games register.
7. After launch, any change to the RNG, scaling or mapping triggers a new test; an approved lab’s annual audit samples updates to check none slipped through.

What RNG certification does not tell you

Certification answers ‘is it fair?’, not ‘will it pay me?’. A certified game with a 96% RTP still keeps 4% of everything staked in the long run. Over 500 spins at 20p, that is £100 staked and an average cost of £4, yet the result of any one session can range from losing most of the £100 to a sizeable win, depending on volatility.

Speed of play is not part of RNG certification. The 2.5-second minimum per spin, the autoplay ban and the turbo ban are tested by the licensee before release. See the game cycle page.

How to check a slot’s RNG certification yourself

Players rarely see an actual lab report, and a badge on a website proves little on its own. What you can confirm is the licence that makes certification compulsory, and the information the game must show you.

1. Find the casino’s Gambling Commission account number in its footer and check it on the Commission’s public register.
2. Open the slot’s help screen and read the RTP and rules; RTS 3 requires them before you stake. Our game help screen entry explains what to look for.
3. If a casino publishes a certificate, check it names a lab on the approved list, gives a date and reference, and covers the platform you are using.
4. Treat sites without a UK licence as outside this system entirely, whatever logos they display.

Fairness complaints go first to the operator; if eight weeks pass without a resolution, the operator must offer referral to an approved ADR provider. eCOGRA is both an approved test house and one of the Commission’s approved ADR providers, which is worth knowing if a certificate and a dispute route carry the same name.

Playing RNG-certified slots online in the UK

The offers below are from Coral, Ladbrokes and PlayOJO, all licensed by the Gambling Commission, so the slots they offer to British players fall under RTS 7 and the testing rules above. Which games each lobby carries changes over time, so search for a title and read its help screen before playing.

Offers are for new customers aged 18+ and terms apply. Coral: deposit and bet £10 on slots for 100 free spins on selected games at 10p each, valid 7 days, with no wagering on spin winnings; the offer runs 1 October 2026 to 1 February 2027 and some payment methods do not qualify. Ladbrokes: deposit and spend £10 on slots for 50 free spins a day for 10 days (up to 500), 10p each, no wagering. PlayOJO: 80 free spins on Big Bass Bonanza at 10p each with a first deposit of at least £10, no wagering, not available in Northern Ireland. Coral and Ladbrokes are run by the same company, so one person may not qualify at both.

18+. Gambling should be entertainment that costs money, not a way to make it. Decide a budget before you play: plan a slot budget. Free, confidential help: National Gambling Helpline 0808 8020 133.