A method for validating input received from an XML based form using reusable XPath validation expressions. The method can include a step of identifying a reusable XPath validation expression including at least one substitution marker. The substitution marker can be mapped to one or more values specific to an XML instance. At least one field to be validated with the reusable XPath validation expression can be designated utilizing the development tool. The development tool can automatically replace the substitution marker with the appropriate value specific to an XML instance.