[Browser Extension] WaniKani Kanji Highlighter 2021

:warning: This is a third-party script/app and is not created by the WaniKani team. By using this, you understand that it can stop working at any time or be discontinued indefinitely.

WaniKani Kanji Highlighter

Chrome Web Store Mozilla Addons

I created this browser extension, already published on Chrome Web Store and Mozilla Add-ons, where it highlights kanji on any web page. I have seen some posts in the past with similar apps, but I think they were outdaded (didn’t work with the new API version anymore).
Other than just highlighting the kanji, if you hover over it, you will get a popup with detailed information about that kanji (this text is from Mars 2021).

2023 Update

August 21st, 2023

Changelog v1.0.0

- Migration to Manifest v3


  • Changed background from Page to Service Worker
  • Window.localStorage not accessible on Service Worker so changed it to IndexedDB
  • Popup is no longer entirely created with Javascript (it is now more organized and with each page on a different HTML file)


  • Improved interface in general
  • Added navbar to Changelogs list in the About page
  • Added “load more” button to Search Results to limit the number of results and reduce lag while writing on search bar
  • Added loading feedback popup for the user to understand the loading stages of data from wanikani
  • Loading data from Wanikani is now also being done from the extension Popup (no need to browse a web page)
  • Progression Bar, Progression Stats and Levels in Progress now show a list of all the related subjects when clicked
  • Lists of subject tiles are now justified to fill the entire width


  • Added new Kana Vocabulary from Wanikani

Bug Fixes

  • Fixed issue where the Subjects Progression Stats would not update over time

Web Page

On any webpage (except within wanikani.com), practically all Kanji taught on WaniKani will be highlighted, with the possibility to distinguish between Kanji learned, and not learned yet. The following interactions can happen:

  • You can hover with your mouse over one of those kanji

  • Then, a small popup will show up in the bottom right corner with basic information of the kanji (the main meaning, readings and the kanji itself). You can hover with the mouse over this popup too

  • The popup will expand and will show more detailed information about that kanji. To make it collapse, just click on anywhere on the page that is not the popup

Extension Popup

You can also use the Extension Popup (button on the top right corner of the browser with the WaniKani Kanji Highlighter logo on it). Here, you can find the following:

  • List of Kanji that were highlighted on the page

  • Information on Lessons and Reviews

  • Search all subjects from WaniKani

  • Customize the usage experience on Settings

  • Prevent the Scripts from running on any page

  • And more…

All Kanji from the extension popup, when clicked, will trigger the Details Popup (on the right side of the screen), within the web page you’re on.

I will keep improving the app, but it will definitely have some bugs.
If you feel like it, you can report bugs to my email: wkhighlighter@diogocorreia.com
Finally, you can also rate the app or give it a review at WaniKani Kanji Highlighter - Chrome Web Store or at WaniKani Kanji Highlighter – Get this Extension for 🦊 Firefox (en-US)
For more information, you can check it on Github.


That’s a cool extension! thanks for posting.

Does it only highlight the Kanji? or is there an option to make the Kanji BOLD instead? or even just change the colour of the Kanji without the highlighting.

I feel like I would get so distracted from the highlighting haha :smile:.

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Thank you!
There isn’t. But I will definitely add it! Thank you for the suggestion.

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I just tested your plug-in for about ten minutes.

I went on the japanese wikipedia and asahi newspaper to see how it looked and felt. First it appeared to miss out on a few Kanji here and there. For example in a sentence the plugin highlighted occasions of 新 but not consistently for some reason.

That was on this articles text.

Also it would be really nice, if the plugin would pick up on the actual vocabulary that is used instead of the Kanji only.

Another thing that doesnt bother me much but I still feel like it’s worth mentioning is, that the Kanji in the headlines will be spaced out from one another. On the right hand side though, where they mention other articles, this effect will lead to sentences being spread out into rows of single kanji making it pretty much impossible to read.

I hope this critique helps updating the code. I sincerely look forward to it.

Great work so far, thanks a lot for sharing this with the community.

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Thank you for taking the time with the extension and for spotting those bugs. I am going to take the time and fix them for sure.
About highlighting the vocab instead of only the kanji, I will keep that in mind for future updates!
If you think that the bugs only happen on a specific website, you can blacklist it so that the extension won’t run on it.

I probably won’t use this, but why only kanji you’ve learned so far? Maybe a different effect for kanji which will be learned later on in WK would be nice as well? And then no info for kanji not on WK, so you know you have to learn those on your own.


is i possible to create this extension for firefox?

If it shows kanji until my current level it is very useful!

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Thank your for your feedback! That does make sense to let the user know whether he will learn a kanji on wanikani or not. I’ll keep that in mind for future updates.


I’ll look into making extensions for firefox and see if I can do it!


Cool extension!
Here’s a feature which could be useful, too: when visiting a website, kanjis which I have never seen on wanikani could be “translated” to hiragana automatically. What do you think?

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Thank you!
That would be great, but unfortunately many kanji have several readings!


Oh right, didn’t think about that.

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@digas99 I love this, thank you so much for your hard work and effort - it’s really enriching the reading experience for me! :smiley:

I usually use RikaiKun (hover-over kanji info popup) but having your sidebar ‘always on’, it’s really reinforcing non-burned items! Keep up the great work :clap:

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I’m glad to see that the app is being of help and thank you for the feedback!

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Amazing idea! And it works like a charm :slight_smile:


I’m very happy to see that you enjoyed it! I will keep improving it!

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It’s an amazing extension, thank you!

The possibility of adding custom kanji/vocabulary would be a nice addition.

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Thank you! I’m very glad you like it!

That sounds interesting, I’ll look into it for future updates!

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I’m trying to enter my (V2) key, and the only thing I get is an alert with “Local data cleared! This didn’t affect your WaniKani account!”, after which it stays on the “Input the key here…” screen. The alert pops up in front of “Subscription not active”, which is never shown as the popup is immediately reloaded.

Is a subscription strictly necessary for the extension to function?

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Yes, unfortunately I haven’t yet setup things so that people without subscription can use the extension, I’m sorry about that! I will look into it and hopefully I’ll implement it soon. About the local data cleared message, don’t worry, it is just the data related to the extension itself.