How to make sure that ETags are not used to track you on the Internet

Martin Brinkmann
Mar 11, 2014

While cookies are still being used widely to track users on the Internet, recent privacy-related developments have forced marketers and companies to experiment with different means of tracking users on the Internet.

One method that has been in use for at least several years uses so called ETags to track users. ETag, which stands for Entity Tag, is a HTTP response header that is primarily being used for caching.

Think of an ETag as a unique value that a web server assigns to each cached element. This unique value is then compared in consecutive visits by the server to determine whether the cached file needs to be replaced. If the identifier differs, the new element is downloaded from the website and a new unique identifier is assigned to it.

Since unique identifiers are assigned to cache resources, ETags can be used to track users on the Internet. What makes ETags special is that it takes some expertise to spot them.

While most Internet users are aware of cookies either directly through the web browser's cookie management option or third-party services such as Disconnect or Mozilla Lightbeam, it is difficult to spot ETags without proper tools such as the Live Headers add-on for the Firefox web browser.

To test this right now in your browser of choice, visit and check the information under Zombie Cookie. Here you should see ETag information next to others.

Finding out if a site uses ETag

Not every website that is making use of ETag is using it to track you. The primary purpose is caching, but if you want to be on the safe side, you will handle all ETags the same way.

You have several options to check if a site uses ETags. The aforementioned Firefox add-on displays the information when you right-click on a page and select View Page Info > Headers.

You do not need to use a browser extension for that though.



  1. Load the web page that you want to test.
  2. Hit F12 to open the Developer Tools.
  3. Switch to the Network Tab.
  4. Reload the page.
  5. Check the main page element first, usually at the top.
  6. ETag should be listed under Response Headers on the right side.



  1. Hit F12 to open the browser's Developer Tools.
  2. Switch to Network.
  3. Load the website that you want to check.
  4. Make sure the main element is selected.
  5. Locate the ETag information under Request Headers on the right.

Internet Explorer


  1. Hit F12 to open the Developer Tools.
  2. Switch to Network.
  3. Click on Start capturing.
  4. Load the website you want to check.
  5. Change to the response headers tab.
  6. Locate ETag here.

How to delete ETags

Since caching is used to set ETags, clearing the browser cache will remove them. While they will be set the next time you visit the site, they cannot be compared by the site anymore and cannot therefor be used to track you across sessions.

To find out how you can configure your browser to clear the cache, check out our guide that explains how to do so.

You can alternatively use third-party programs such as CCleaner to clean the cache of all browsers regularly.


Tutorials & Tips

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  1. ilev said on August 4, 2012 at 7:53 pm

    Doesn’t Windows 8 know that www. or http:// are passe ?

    1. Martin Brinkmann said on August 4, 2012 at 7:57 pm

      Well it is a bit difficulty to distinguish between domains and files for instance.

    2. Leonidas Burton said on September 4, 2023 at 4:51 am

      I know a service made by google that is similar to Google bookmarks.

  2. VioletMoon said on August 16, 2023 at 5:26 pm

    @Ashwin–Thankful you delighted my comment; who knows how many “gamers” would have disagreed!

  3. Karl said on August 17, 2023 at 10:36 pm


    The comments section under this very article (3 comments) is identical to the comments section found under the following article:

    Not sure what the issue is, but have seen this issue under some other articles recently but did not report it back then.

  4. Anonymous said on August 25, 2023 at 11:44 am

    Omg a badge!!!
    Some tangible reward lmao.

    It sucks that redditors are going to love the fuck out of it too.

  5. Scroogled said on August 25, 2023 at 10:57 pm

    With the cloud, there is no such thing as unlimited storage or privacy. Stop relying on these tech scums. Purchase your own hardware and develop your own solutions.

    1. lollmaoeven said on August 27, 2023 at 6:24 am

      This is a certified reddit cringe moment. Hilarious how the article’s author tries to dress it up like it’s anything more than a png for doing the reddit corporation’s moderation work for free (or for bribes from companies and political groups)

  6. El Duderino said on August 25, 2023 at 11:14 pm

    Almost al unlmited services have a real limit.

    And this comment is written on the dropbox article from August 25, 2023.

  7. John G. said on August 26, 2023 at 1:29 am

    First comment > @ilev said on August 4, 2012 at 7:53 pm

    For the God’s sake, fix the comments soon please! :[

  8. Kalmly said on August 26, 2023 at 4:42 pm

    Yes. Please. Fix the comments.

  9. Kim Schmidt said on September 3, 2023 at 3:42 pm

    With Google Chrome, it’s only been 1,500 for some time now.

    Anyone who wants to force me in such a way into buying something that I can get elsewhere for free will certainly never see a single dime from my side. I don’t even know how stupid their marketing department is to impose these limits on users instead of offering a valuable product to the paying faction. But they don’t. Even if you pay, you get something that is also available for free elsewhere.

    The algorithm has also become less and less savvy in terms of e.g. English/German translations. It used to be that the bot could sort of sense what you were trying to say and put it into different colloquialisms, which was even fun because it was like, “I know what you’re trying to say here, how about…” Now it’s in parts too stupid to translate the simplest sentences correctly, and the suggestions it makes are at times as moronic as those made by Google Translations.

    If this is a deep-learning AI that learns from users’ translations and the phrases they choose most often – which, by the way, is a valuable, moneys worthwhile contribution of every free user to this project: They invest their time and texts, thereby providing the necessary data for the AI to do the thing as nicely as they brag about it in the first place – alas, the more unprofessional users discovered the translator, the worse the language of this deep-learning bot has become, the greater the aggregate of linguistically illiterate users has become, and the worse the language of this deep-learning bot has become, as it now learns the drivel of every Tom, Dick and Harry out there, which is why I now get their Mickey Mouse language as suggestions: the inane language of people who can barely spell the alphabet, it seems.

    And as a thank you for our time and effort in helping them and their AI learn, they’ve lowered the limit from what was once 5,000 to now 1,500…? A big “fuck off” from here for that! Not a brass farthing from me for this attitude and behaviour, not in a hundred years.

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