Best jQuery Form Validation Plugins & Tutorials with Demo

jQuery validation engine is a Javascript plugin aimed at the validation of form fields in the browser (IE 6-8, Chrome, Firefox, Safari, Opera 10). The plugin provides visually appealing prompts that grab user attention on the subject matter.

Validations range from email, phone, and URL, to more complex calls such as ajax processing or custom javascript functions. Bundled with many locales, the error prompts can be translated into the language of your choice.
Rules of thumb
* field.id are **unique** across the page
* for simplicity and consistency field.id and field.name should match (except with minCheckbox and maxCheckbox validators)
* spaces or special chars should be avoided in field.id or field.name
* use lower cases for input.type ie. *text, password, textarea, checkbox, radio*
* use the Ajax validator last ie. validate[custom[onlyLetter],length[0,100],**ajax[ajaxNameCall]**]
* use only one Ajax validator per field!
* JSON services should live on the same server (or you will get into browser security issues)
* in a perfect RESTful world, http **GET** is used to *READ* data, http **POST** is used to *WRITE* data: which translates into -> Ajax validations should use GET, the actual form post should use a POST request.

jQuery.validity is a jQuery plugin for powerful, accurate client-side form validation. It is well-organized, versatile and can easily tackle any validation problem.You can use to setup client-side form validation. Instead of writing validation manually or balancing some unwieldy server-side framework, validity allows you to design client-side validation in a manner that feels natural and straightforward.

jQuery.validity takes advantage of jQuery’s selector engine to perform validation on logical groupings of inputs, making it declarative and clean. This means that the inputs on a page can be added, removed, or changed and validation will still work without reconfiguration.

jQuery.validity is designed to give you total control over how validation messages appear, so you can easily adapt the way validation errors are displayed to the look and feel of your site.