You do not necessarily need formal qualifications to become a developer, but you will need a good knowledge of 'front end' concepts (how the site looks and functions for the user), and 'back end' systems (how it works).
You will need to be familiar with common operating systems and servers, databases and web programming, networking and security, and graphics, animation and web design software.
Employers will want to see evidence of your experience along with any qualifications you may have.
You should keep a portfolio of work, demonstrating your creative and technical ability. This can be in the form of a CD, DVD or 'live' website.
If you lack commercial experience, developing and designing a site for a local community group or voluntary agency could be used in your portfolio.
Many new entrants now have a foundation degree, BTEC HNC/HND award or degree, which will usually be in an IT-related subject such as web development or web design; multimedia design; digital media development; web content management; business information systems; computer programming.