Awesome
gulp-w3cjs 
Usage
First, install gulp-w3cjs as a development dependency:
npm install --save-dev gulp-w3cjs
Then, add it to your gulpfile.js:
var w3cjs = require('gulp-w3cjs');
gulp.task('w3cjs', function () {
return gulp.src('src/*.html')
.pipe(w3cjs())
.pipe(w3cjs.reporter());
});
Custom Reporting
The results are also added onto each file object under w3cjs, containing success (Boolean) and messages (Array).
Example usage
var w3cjs = require('gulp-w3cjs');
var through2 = require('through2');
gulp.task('example', function () {
return gulp.src('src/*.html')
.pipe(w3cjs())
.pipe(through2.obj(function(file, enc, cb){
cb(null, file);
if (!file.w3cjs.success){
throw new Error('HTML validation error(s) found');
}
}));
});
Example output
HTML Error: index.html Line 5, Column 19: Element title must not be empty.
<title></title>
.../gulpfile.js:11
throw new Error('HTML validation error(s) found');
^
Error: HTML validation error(s) found
API
w3cjs(options)
options.url
URL to the w3c validator. Use if you want to use a local validator. This is the
same thing as w3cjs.setW3cCheckUrl().
options.proxy
Http address of the proxy server if you are running behind a firewall, e.g. http://proxy:8080
options.doctype and options.charset were dropped in 1.0.0. Use 0.3.0 if you need them.
options.showInfo
Default: false
Show info type messages in the output.
options.verifyMessage
Allows you to intercept info, warnings or errors, using options.verifyMessage methed, returning false will skip the log output. Example usage:
return gulp.src('index.html')
.pipe(w3cjs({
verifyMessage: function(type, message) {
// prevent logging error message
if(message.indexOf('Element “style” not allowed as child of element') === 0) return false;
// allow message to pass through
return true;
}
}))
.pipe(w3cjs.reporter())
w3cjs.setW3cCheckUrl(url)
Same as options.url. SEt's the URL to the w3c validator.