SVG Validator

From Svg wiki

SVG viewers don't detect all errors in content claiming to be SVG, let alone report them. SVG editors don't always produce content conforming to the specification. Anything that is not valid SVG will result in unpleasant surprises at some point. Validators like http://validator.w3.org and http://jiggles.w3.org/svgvalidator can help you detect errors.

Viewers have limitations so just making sure your SVG content is valid is not all you can do. Reporting those limitations is important to have them fixed, so please do. Some viewers, like for example the Adobe Plug-In, will never get fixed. Others might not be fixed seconds after you report them, which is probably too late for the project you're working on at that moment. Dodging those limitations is usually pretty well possible though. Very valuable resources for this like authoring guidelines, bug databases, etc, are available. It would however be easier if a validator could give you warnings about viewer limitations. Some experiments (that you are welcome to help on) in this field are now hosted on openclipart.org and now mentioned among other useful tools on http://openclipart.org/wiki/SVG_Testing