Frequently Asked Questions

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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.

Learn more  about markup validation.

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:

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.

How do I write a new validation service to be part of Unicorn?

See our information about developing a new service for Unicorn.

How can I contribute code to the Unicorn project?

See information about contributing code to Unicorn.

Can I download and install Unicorn?

Yes! Unicorn is an open source software which means anyone can download, use, modify and redistribute it freely. Full instructions on how to install Unicorn are available