Online casinos use a computer program called a random number generator (RNG) to generate random numbers for their games. The RNG is a software algorithm that is designed to produce a sequence of numbers that are statistically random and cannot be predicted.

The RNG works by using a seed value, which is a starting point for the algorithm. The seed value is typically based on some external factor, such as the current time or a random event from the environment, to ensure that it is truly random.

Once the seed value is established, the RNG uses a complex mathematical formula to generate a sequence of numbers that appear random. The formula takes the seed value as input and produces a new number as output. This process is repeated many times, with each new output number becoming the input for the next iteration.

The output numbers generated by the RNG are used to determine the outcomes of the games played at the online casino. For example, in a game of online slots, the RNG may generate a series of numbers that correspond to the symbols on the reels. The symbols that appear on the reels are then determined by the numbers generated by the RNG.

To ensure the fairness of the games, online casinos use third-party testing agencies to audit and certify their RNGs. These agencies test the RNGs to ensure that they are truly random and cannot be manipulated.