Validating your code can be a real shocker at times. Although we all try to write standard code, sometimes it just seem an impossible task. One of the growing needs in html today, is for that of a quality html validator (syntax checker). While searching around for my own purposes, I was surprised how few options HTML authors have for validators today.

Summary:

You have your basic two choices, a high quality pricey commercial product, or the official standard freebie.

The Commercial Choice:
The quality commercial package is the CSE HTML Validator.

At $129 USD it is a bit steeper price tag than most of us are use to paying for software these days - but, it is the best thing going in HTML validators. Nothing compares to its features and function. From simple syntax checking to more advanced cascade error preventing tag trees, it does it all.

There is a demo version (50 validations), and a freebie lite version. Even the lite version is better than most of the competition. If you are serious about html development, you need this tool.

http://www.htmlvalidator.com

The Freebie Choice:
The W3C Validation service is straight from the body endowed with creating web standards. It is also free and web based. Simply put in the url you wish to validate and let it run. Opera users have a leg up here with a simple right click and validate to validate any page in the browser.

You may also upload a file from your computer.

The biggest draw back to the W3C validator is it is unforgiving. It is not only strict, it suffers terribly from cascade errors with mismatched tags. Often you'll have to look through hundreds of errors to find the real one that will fix the whole shabang.

The biggest strength though, is that when your page does validate, you are assured that it should be viewable in all modern browsers. It will also correctly deal with the newer languages like XML.

There is also a CSS Validator at the W3C. In a nice touch, you can cut & paste, upload, or validate by url:
http://jigsaw.w3.org/css-validator/

The main page for the W3C validator is located at:
http://validator.w3.org/

Other Validators:

Bobby checks your page for accessibility features: http://www.cast.org/bobby/

Weblint is now becoming dated. It has not been updated in ages. Still has some life left in it: http://www.weblint.org/

Web Design Groups Online Validator. Much in the save vein as the W3C's validator, it allows checking from online by URL and supports a wider group of character encodings:
http://www.htmlhelp.com/tools/validator/

There is also, A Real Validator from Liam Quinn that uses an IE front end. It is good, but lacks the power features of CSE. Shareware.

Another entry is Dave Raggetts HTML Tidy. HTML Tidy actually changes -- or tries -- the source code to the page.
http://www.w3.org/People/Raggett/tidy/

The home team:
http://www.searchengineworld.com/validator/

Finally, the
Yahoo category for validators.

and the
Open Directory Project page on validators.

Anyone know of any worthwhile html checkers I have missed? Possibly for other platforms?
I have always used http://www.netmechanic.com

They were just taken over and their free service has been cut back a little. It will only validate 25 links per page. Other than that it's pretty good. It will allow you to downside .gif & .jpeg graphics.
Anybrowser.com offers two free validators, one for HTML 3.2 and one for strict HTML 4.0.

I've been using the onboard validator with Homesite. Since I usually write my code in Homesite, it's right at hand. It's extremely configurable, which I appreciate very much -- sometimes I'm not trying for totally strict code but just editing a buggy page for someone just to get it to work.

Homesite does tend to suffer from cascading errors, especially with some simple things like unclosed quotes, but to be fair, I'm using an older version. Recent releases may be improved.

I'm curious about this freeware, arachnophilia. I have a friend who swears by it. It's a lot more than a validator -- they call it a website workshop and it has a huge features list including spell check, browser integration for 6 browsers, FTP client, on and on. Amazing for freeware. Is anyone using it?
One feature of HTMLtidy is that it can help make the conversion to XHTML. I'm not sure I can deal with running from the command line, but there seem to be some third party GUI's out there if the going gets too rough.
I have tried arachnophili now for a whole hour. It looks interesting. I always liked those beautify code options. Althought I am still investigating, it is pretty impressive for free ware.

I think the best thing about the produce is the wizards that do tables and frames. That could be a real help and I think I will be using that option in the future for no brainer development to save all that redundant typing. The validator/analyzer is rather rudimentary, but could be useful.

>Anybrowser

They use WebLint and the actual W3C validator.
btw: the WDG validator and A Real Validator are written by the same author (Liam Quinn).

I also forgot about Delorie.coms Web Page Purifier:
http://www.delorie.com/web/purify.html
I also have a validator for XML/XHTML on my site at http://www.xoc.net/tools/xmlvalid . It won't spider, though, and doesn't do HTML.
With the coming rumored switch of AOL to Netscape, validation is more important than ever.

Are you ready?
I thought everyone was using the W3C validator!

Sorry Brett-

Would you mind elaborating just a tad on what the transition will mean exactly?
Tedster > arachnophilia... Is anyone using it?

Arachnophilia has been my html editor for close to a year. It's a great tool. I code by hand so I haven't utilized many of the features, but I do use the spellcheck, find/replace, search and the syntax checker. I also like the way it displays the mark-up; real easy to discriminate page divisions, tables etc. Free is also a very good price!
arachnophilia... Is anyone using it?

I've used arachnophilia for about a year. You get a lot for a reasonable price. Just downloaded the new Java version but have not tried it yet.

BTW, anyone try out that new SuperHay Validator - they say cows can really crank out some great code with it.
Homesite v.5 Tidy (set to XHTML) - it almost makes it impossible to write invalid code....

I have dug into Tidy's config files and set it up to pretty-up the pages and balance the whitespace. The result is very neat (& pretty!) code that is a breeze to go back and edit any time I get the hankerin' ...

Homesite's Validator and Opera's - I'm good to go!

XHTML CSS VALIDATED CODE=Peace of Mind! :)
There's also the Java version of Tidy -- JTidy. I have a bugbear about laying out html (it makes life easier later) even if it is computer generated.

JTidy (and possibly Tidy) have one or to slight flaws/features in that they're quite picky...
Homesite's on board validator used to be CSE. Is that still the case in Homesite 5?

Also, CSE is powerful, but it isn't a true SGML parser - so it can miss errors and report errors that aren't really there. The new release probably improves on this.
I am happy with BBEdit's (Mac) HTML verification utility as well as it's text colorings.

However I find it lacking in it's HTML beautify (I find it goes a bit overboard with putting every single tag on a separate line) and no CSS verification.
I am using HTMLKit and it has a validator, converts to XHTML and suggests CSS. It is Freeware and I have liked it better than any other editor to date. I don't know how the vaildator compares to others but the interface and options are great (especially for freeware)
I use the W3C validation tool exclusively. I figure if you can validate at the W3C, you can validate anywhere! And since they are the authority...

I also use NN4.7. ;)
>freeware, arachnophilia

Ahem, colegas. Arachnophilia is actually 'careware', and after lurking here a couple of months I'd say you all qualify.
Seriously though, I've used Arach for about 3 or 4 years now, in fact that and a squeaky new netscape com 3 helped me begin understanding html. Now I'm looking for a way to finish understanding it.
Really a very useful tool with many possibilities which are not exploited by me, sadly. The arachnoid website I found quite interesting, at times humourous, and with info about the prog.
Just about all our sites are dyanamic or embedded lanugages like php. That leaves some pretty special considerations when it comes to validation.

I use Opera with is's handy shift-ctrl-v key to validate (url changed to a local version of the sew validator).

I temporarily switch the view source program to point at CSE. So a control-f3 sends the source to cse and a f6 validates it. (umm, cse is awesome. I wish they had an affiliate program)

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