A tool to do validation of your HTML generated from your Django app. Python 3 compatible.
License: MPL 2
If you don't download a local
vnu.jar file (see below), it will use
validator.nu and send your HTML there.
If you use
htmlvalidator to validate tests it's unlikely your HTML contains
anything sensitive or personally identifiable but if you use the middleware
option there's a potential risk.
First things first, very simple:
pip install django-html-validator
Note, it won't do anything until you chose how you want to use it and you also need to explicitly enable it with a setting.
Basically, you have a choice of how you want to use this:
- As a middleware
- In your unit tests (technically they're integration tests in Django)
If you chose to set it up as a middleware and enable it accordingly it will run for every rendered template in the tests too. Not just when you run the server.
Independent of how you use
htmlvalidator you need to switch it on.
It's not on by default. The setting to do that is:
HTMLVALIDATOR_ENABLED = True
What this does, is that it prints all validation errors to
But it doesn't stop the execution from running. Even if there are errors.
To make it so that the execution stops as soon as there is any validation error switch this on in your settings:
HTMLVALIDATOR_FAILFAST = True
Now, if there's any validation error going through the client you'll
htmlvalidator.exceptions.ValidationError exception raised.
Equally, if you're running it as a middleware and have this setting on it will raise the exception in the request.
When validation errors and warnings are encountered,
dump the HTML to a file and the errors in a file with the same name except
with the extension
.txt instead. It will dump this into, by default, the
systems tmp directory and in sub-directory called
/tmp/htmlvalidator/. If you want to override that change:
HTMLVALIDATOR_DUMPDIR = '~/validationerrors/' # default it /tmp
Whatever you set, the directory doesn't need to exist but its parent does.
By default when
htmlvalidator encounters validation errors it stores
the relevant HTML file in the
HTMLVALIDATOR_DUMPDIR together with a file
with the extension
.txt in the same directory. Alternatively you can just let
it dump the validation errors and warnings straight onto stdout with:
HTMLVALIDATOR_OUTPUT = 'stdout' # default is 'file'
Setting the vnu.jar path
By default, all validation is done by sending your HTML with HTTP POST to html5.validator.nu.
Not only does this put a lot of stress on their server. Especially if you have
a lot of tests. It's also slow because it depends on network latency. A much
better way is to download the
vnu.jar file from their
latest release on
You set it up simply like this:
HTMLVALIDATOR_VNU_JAR = '~/downloads/vnu.jar'
This also requires java to be installed because that's how
.jar files are
executed on the command line.
Be aware that calling this
vnu.jar file is quite slow. Over 2 seconds is
not unusual. A faster alternative is to use the
vnu.jar to run a local web
instance of the validator, and pointing validation to use that by NOT setting
HTMLVALIDATOR_VNU_JAR and doing this instead:
HTMLVALIDATOR_VNU_URL = 'http://localhost:8888/'
The local web instance of the validator can be started typically by:
java -cp vnu.jar nu.validator.servlet.Main 8888
Validating during running the server
A way to do HTML validation is to do it during running the
server. E.g. with
To do that you need to enable the middleware. In your settings module,
MIDDLEWARE_CLASSES for example like this:
if HTMLVALIDATOR_ENABLED: MIDDLEWARE_CLASSES += ("htmlvalidator.middleware.HTMLValidator",)
You can also add it directly and unconditionally to
and it won't do anything (except be loaded) unless enabled, see
the note above about
HTMLVALIDATOR_ENABLED for more info.
Also, if you enable
HTMLVALIDATOR_FAILFAST, when running the
htmlvalidator middleware it will raise an exception as soon as it
sees some invalid HTML.
Validating HTML in tests
Suppose you have a class that does tests. By default it already has a
self.client which you use to make requests. All you need to do is to
replace it with the
class. For example:
from django.test import TestCase from htmlvalidator.client import ValidatingClient class MyAppTests(TestCase): def setUp(self): super(MyAppTests, self).setUp() self.client = ValidatingClient() def test_homepage(self): response = self.client.get('/') self.assertEqual(response.status_code, 200)