Messaging has an important role to play in reducing gambling harm. Safer gambling messaging comprises, for example, advertisements that appear on television, or notifications that appear on-screen when logged into an online gambling platform. Recent evidence indicates that a generic warning label approach may not be effective , and consequently a more individualised, operator-led approach might have more impact. However, much of the evidence is from laboratory studies or experiments conducted away from the environments in which people would normally gamble and there are some questions about how well the evidence might generalise to a more natural setting. This impact evaluation aims to complement existing research by examining safer gambling messaging as implemented by gambling operators on their customers in live play.