Be concise and call for an action first, e.g.: Please use a modern browser to view this website. We recommend Firefox, Chrome or Safari. These browsers support

Be concise and call for an action first, e.g.: Please use a modern browser to view this website. We recommend Firefox, Chrome or Safari. These browsers support some of the advanced features used to build this website. You need to be friendly and polite, but there is no need for a lot of boilerplate language to sugarcoat it. You could caption it with something like "Internet Explorer 6 is not supported". That being said, why do you need to exclude older clients from your app? Javascript frameworks tend to make supporting a wider range of clients relatively effortless, by providing fallbacks. I would only exclude users based on their browsers for backend applications targeted at a small group of tech-savvy users and if building something that degrades well isn't viable within the scope of your project. The latter also depends on what kind of project it is (if its a small hacking project or a demonstration of some HTML5 functionality I totally get not being bothered with supporting IE7). In my own work I make sure everything works and doesn't look embarrassingly ugly in older browsers, while some minor presentation details (e.g. shadows) are only visible in bleeding edge clients.