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Yo! Check your HTML!

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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 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:


What this does, is that it prints all validation errors to stdout. 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:


Now, if there's any validation error going through the client you'll get a 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, htmlvalidator will 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 htmlvalidator. E.g. /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

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 GitHub page.

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 ./ runserver.

To do that you need to enable the middleware. In your settings module, append htmlvalidator.middleware.HTMLValidator to MIDDLEWARE_CLASSES for example like this:

    MIDDLEWARE_CLASSES += ("htmlvalidator.middleware.HTMLValidator",)

You can also add it directly and unconditionally to MIDDLEWARE_CLASSES 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 htmlvalidator.client.ValidatingClient 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)

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django-html-validator-0.5.1.tar.gz (6.7 kB view hashes)

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