is W3Cs unified code markup, CSS, RSS feed, and links validator service.
Unicorn is W3C's unified validator, which helps people improve the quality of their Web pages by performing a variety of checks. Unicorn gathers the results of the popular HTML and CSS validators, as well as other useful services.http://validator.w3.org/unicorn/
This site addresses these audiences:
Users, those who want to check their Web pages and understand how to fix them based on Unicorn results.
Developers, those who wish to add new services, work on existing services, or help develop the underlying Unicorn framework.
Server Managers, those who wish to run their own Unicorn service locally.
Make a donation to support the free Unicorn service and see the site for providing feedback or reporting a bug.
Use Unicorn - Make the Web Better!
Learn more about how to use Unicorn to improve the quality of your Web pages.
The Unicorn interface is available in more than 20 languages. Help make Unicorn available in your language by adding a translation or improving an existing one.
To jump into Unicorn, just provide a URI and push the button. Unicorn will call a series of validation services and report the results.
The Unicorn interface gives you additional control over what you want to validate and what tests to perform. More information for users is available in the FAQ. People who want to learn more about developing validation services or Unicorn itself should refer to links on the Unicorn home page.
What do you want to validate?
You can tell Unicorn what to validate in any of the following ways:
By identifying a page on the Web with a URI.
By uploading a file (useful when your page isn't yet on the Web). Choose the "By File Upload" tab for this option.
By pasting markup directly into a form. Choose the "By Direct Input" tab for this option.
What services do you want Unicorn to perform?
By default, Unicorn performs all the checks it can for the type of document you tell it to validate. This is the "General Conformance Check" option under "Select a task"
You may also choose individual tasks in the same pulldown menu, such as (just) "CSS Profile Validation" or (just) "mobileOK checking". Individual checkers may offer "advanced options," for example whether the CSS validator should display errors and warnings, or just errors.
In the task pulldown menu, there is also a "Custom task" pulldown. When you choose this, you may choose which tests you wish to perform from the validation services known to Unicorn. Note that some validation services may not make sense for certain types of content (and those services will let you know)!
What is Unicorn?
Unicorn is W3C's unified validator, which helps people improve the quality of their Web pages by performing a variety of checks. Unicorn gathers the results of the popular HTML and CSS validators, as well as other useful services.
What does "validation" mean?
Validation is a process of testing some piece of content (HTML, CSS, etc.) against a set of rules. The HTML validator determines whether the markup conforms to the grammar of HTML (e.g., as expressed through a document type definition, or DTD). The CSS validator determines whether the CSS rules conform to CSS syntax.
How do I get started making my pages valid?
See Making your website valid: a step by step guide and see other resources on Web quality.
What validation services does Unicorn perform?
Today Unicorn aggregates results from the following tools:
Markup validator (HTML, XHTML, ...). See also the Markup validator FAQ.
CSS validator. See also the CSS validator FAQ.
Feed checker (RSS, Atom). See also the Feed validator FAQ.
Unicorn reports false positives!
Unicorn gathers results from other validators and Web Services. Unicorn reporting errors means the corresponding validator did report errors. If you believe this is wrong, you should contact the maintainer of this validator directly as Unicorn is not faulty here.