Is there a plugin for Firefox to validate HTML 5?
I've always used HTML Validator, but if my webpage has a <!DOCTYPE HTML> doctype, the version I use [edit: prior to the December 2010 0.904, which introduced support] complains about it not having a doctype at all.
I specifically would like one similar to HTML Validator, where the verification happens on your computer, instantaneously and automatically, without needing to send any data to a third-party server and then wait for a reply.
This is the best one I found so far:
https://github.com/rogerjohansson/html5validator (see Downloads for an xpi)
You should not use the validator.nu online service with it, since it causes a DoS attack on the online service, and you will probably be banned from using the service as a countermeasure (see https://github.com/rogerjohansson/html5validator/issues/6). The cool thing is, it does not send the URL to the validator, but the HTML data directly; this means that local sites or password-protected sites can also be checked.
Validation can be turned on automatically, by a domain-whitelist or by clicking the validator item.
You can and should up your own validator.nu-instance (at least on Linux and Mac OS X) - see this. You would then have a locally-running validator and can even check sites without an Internet connection by filling in http://localhost:8888/ (the default address of the local validator instance) into the Validator URL of the addon.
To give credits: I have the information above from Validating HTML5 with validator.nu and the HTML5Validator Extension for Firefox.
On the Web Developer add-on, https://addons.mozilla.org/en-US/firefox/addon/60, if you use "Tools" > "Display Page Validation" it will show a bar at the top validating the page source code. This is done via the W3C validator, but without you having to navigate there.
It is a shame the HTML Validator has no plans as of yet to incorporate HTML5 until at least version 0.9.
Although that was not possible when you asked, the very extension you mention supports that (since December 2010's version 0.904 [which they also sometimes call 0.9.0.4]). HTML Validator by Marc Gueury appears to be the best option, allowing to choose between client-side and server-side (relying on a W3C service) validation.
This says it will do it: https://addons.mozilla.org/en-US/firefox/addon/2318 and I found this also: http://html5.validator.nu/
You can validate HTML5 at the following site:
Make sure on the options that you select the HTML5 document type.
