The decoy effect (also known as the attractiveness heuristic) is a phenomenon in behavioural economics in which a third choice (the "decoy") in a comparison with another option helps to influence the choice decision in favour of the preferred option. The decoy is an option that is not a realistic choice, but is designed in such a way that it increases the attractiveness of one of the other options.

In neuroweb design, the decoy effect can be used to increase the conversion rate on a website. By adding a decoy element, the customer can be subtly persuaded to choose a particular option. An example of this could be a website that offers a basic product and a premium product. By adding a decoy element, such as a more expensive product with additional features, the premium product can appear more attractive and influence the customer's decision in favour of the premium product.

The decoy effect can also help to increase customer decisiveness by providing a third option that facilitates a clear decision. On a website, for example, this could be achieved by adding a third price option that makes it easier to choose between the other two options.