Troubleshooting Web Lab problems


Web Lab Disallowed Elements 

In order to keep Web Lab protected from security vulnerabilities and prevent it from being used to host malicious projects, certain HTML elements are not allowed: <iframe> and <script> tags, and the <meta> tag was restricted to block the 'http-equiv' attribute. This means that the <meta> tag is still supported, but not in combination with the 'http-equiv' attribute. As you are editing code in Web Lab, if any blocked elements are added to a project they will be automatically removed from the project and a warning will pop up. 

If you would like to use <iframe> tags, <script> tags, or <meta> tags with the 'http-equiv' attribute in your projects, we recommend switching to a different web editing environment, such as

Web Lab Loading Issues

Web Lab will sometimes fail to load, with an infinite spinner or with the following error:


We're sorry, Web Lab failed to load for some reason.  Please see our support article "Troubleshooting Web Lab problems" for more information.

We've compiled a list of possible solutions to this problem:

Unblock Web Lab domain names

Web Lab has some unique IT requirements among tools; in particular, it uses a couple of additional domain names for security reasons.  Sometimes schools restrict access to these domains, which can cause issues.  Please work with your IT department to ensure your devices allow full access (including cookies) for these domains:


See our IT Requirements page for more details.

Clear browsing data

A few teachers (in particular, those seeing this problem on Chromebooks) have reported that clearing the cookies and cache on their students' devices solved the problem.

No private browsing

Web Lab is known not to work in private browsing / incognito modes for most browsers. Please make sure you are not using one of these modes to access Web Lab.

Try a different browser

If your students have access to more than one web browser, please have them try using a different one.  We've had reported problems in Chrome that were fixed by switching to Firefox, and reported problems in Firefox that were fixed by switching to Chrome.

Update your browser

We've noticed these problems are more common in classrooms where the browser is several versions old.  If you have access to do so, please try updating your web browser to its latest version.

Clear some disk space

We have seen a few cases this error occurs because the computer is low on disk space.  If it looks like your computer is running out of space, deleting some files and freeing up some disk space will probably resolve the problem.

Reset the project

If your student is having trouble with some, but not all, Web Lab levels, it's possible the issue is specific to the project or progress they are trying to load.  Performing a reset on that particular level sometimes solves the problem. They can reset their data for that particular level by following these steps:

  1. Click the Version History button.
  2. In the dialog that opens, click the Start Over button.

Reset Bramble filesystem

Web Lab depends on a browser feature called the IndexedDB API. Occasionally this feature gets "stuck" and must be reset.  We've added a button to the error dialog that reads "Reset Web Lab" - it will attempt to perform this reset and then reload the page.

Check user permissions

In some cases this error occurs for student accounts that have very limited permissions on their device - in particular, we suspect not having write access to certain parts of the file system (especially the browser profile) can interfere with browser features required by Web Lab.  To check this, try signing in as a different user on the same device - perhaps a teacher or administrator - and opening Web Lab.

If signing in as a user with more access resolves the issue, you may need to work with your IT department to make sure student accounts are given sufficient file system permissions to use Web Lab.  We'd also like to hear about this situation - let us know and we'll see what we can do to help.

Contact us

If you are still having trouble with Web Lab, please let us know about your situation so we can explore other options.

Please include the following information with your request:

  • The web browser version and operating system of the affected device. is a good way to find this information.
  • Are all of your students seeing the same problem, or only some of them?
  • If a student runs into this problem, are they seeing it on all Web Lab levels or just specific ones?
  • Does this happen only on student computers or also on the teacher's computer?


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