Web pages are based upon various rules used to create them, and browsers use those rules to display the Web pages consistently. However, no matter what program you use to create your pages, there is a lot of possibility for error. Validating your web pages allows you to catch and correct any problems that may exists and help insure your web pages work as they should.
The links on this page are to HTML validators (these check HTML code for standards compliance and errors), CSS validators (these check Cascading Style Sheets for errors and standards compliance), browser compatibility checkers (these check your pages to see if they are compatible with different browsers), broken/dead link checkers, and accessibility checkers (these check your pages to determine if they are accessible to people with disabilities).
HTML and XHTML Validators
HTML
Tidy (HTML Validator)
Checks your HTML and XHTML web pages for syntax errors. The validator comes
with a syntax highlighting editor that you can use to build your web pages
as well as correct errors. When run on your documents, the validator highlights
lines with potential errors in your code and gives a brief message describing
the possible problems associated with that line.
CSE
HTML Validator Lite
HTML Tidy is not just a HTML validator for your web documents. It is able
to correct bad HTML code and give you pointers to areas where you need to
change in order to make your web page accessible to people with disabilities.
Source code and binaries are available for a wide variety of operating systems,
including Windows 95/98/NT/2000, Mac OS, Atari, Amiga, BeOS, AIX, Linux, UnixWare,
HP-UX, MSDOS, Solaris, OS/2, FreeBSD, RISC OS, MiNT (Atari) OS, etc. There's
also a Java port and an online
version of HTML Tidy.
W3C
HTML Validation Service
Checks your HTML and XHTML web pages either by giving it your web page's URL
or uploading your document directly to the validator. Many people consider
it the authoritative source for checking for standards compliance since the
W3 Consortium is responsible for the various HTML/CSS standards. Source code
for the validator is also available.
Web
Page Purifier
Allows you to check your HTML pages for compliance with various HTML standards
(eg HTML 4.0 Transitional, HTML 4.0 Strict, WebTV 1.1, HTML 3.2, etc). There's
a form where you can enter the URL of the page to check, or you can also download
the Perl CGI source code.
Cascading Style Sheets (CSS) Validators
CSSCheck:
Cascading Style Sheets Lint
A validator for Cascading Style Sheets (CSS) that also checks for some browser
compatibility issues with your style sheet.
W3C
CSS Validation Service
Checks your Cascading Style Sheets either by giving it your web page's URL
or uploading your document directly to the validator. Many people consider
it the authoritative source for checking for standards compliance since the
W3 Consortium is responsible for the various HTML/CSS standards.
Browser Compatibility Checkers
Web
Page Backward Compatibility Viewer
If you need to check your web pages to see if they are compatible with browsers
that lack certain features, this page checker might be useful. You must specify
which features you do not want on a page, like tables, images, etc.
Web Page Accessibility Checkers
A-Prompt
A Windows program that checks your pages for accessibility issues and fixes
the pages for you. It has a Wizard-like interface which guides you through
the potential problems that your web page may have and prompts you for information
for repairing the page.
Bobby
HTML Accessibility Checker
C hecks your HTML pages for areas that might pose difficulties for people
with disabilities. You enter the URL of your web page then gives you a report
after it visits that URL. You can also download Bobby to use on your machine.
It can check your site against the US Section 508 Guidelines, or against the
Web Content Accessibility Guidelines 1.0.
Broken Links Validators
W3C
Link Checker
This online validator from the W3 Consortium is able to recursively check
your document for dead links. You simply enter a URL in the form provided,
and it will visit your site and check the links.
Xenu
Link Sleuth: Find Broken Links
Xenu is a utility for Windows that checks your web site for broken links.
It can work both with a "live" website as well as on a copy of your web site
residing on your own hard disk. It's a favourite of many webmasters for checking
broken links on their site.