The second edition of Mastering ArduinoJson is only one year old, but it already needed a refresh. Indeed, several important changes in the library had to be integrated into the book.

Mastering ArduinoJson 6 Third Edition

What’s new in this edition?

I updated Mastering ArduinoJson with all the changes in the library since the previous edition. Here are the most significant changes:

  • In the second chapter (C++), I explained the difference between von Neumann and Harvard architectures, and the implication on Flash strings. In the past, Arduino boards were mainly Harvard, but with the rise of ESP32 and ARM boards, the von Neuman architecture becomes prevalent.
  • In the third chapter (deserialization), I added the error code EmptyInput and removed NotSupported. I replace all as<char*>() with as<const char*>() because the syntax is now deprecated. Also, since deserializeJson() now decodes Unicode escape sequences by default, I remove every paragraph that warned about this issue.
  • In the fourth chapter (serialization), I updated the GitHub example to use the new interface of HTTPClient. I removed the SSL certificate check because it forced readers to update the footprint before running the program. Of course, I added a paragraph explaining what risk comes with skipping the certificate validation.
  • In the fifth chapter (advanced techniques), I added a new section about custom converters.
  • In the eighth chapter (case studies), I rewrote the configuration file example using custom converters, which greatly improved the code. This is the most important change in the book; I really recommend that you check it out. I decided to keep SPIFFS because LittleFS is still not available in the ESP32 core.
  • Over the whole book, I updated the screen captures, especially the ones of the ArduinoJson Assistant, which changed significantly since the last edition.

There are also countless small improvements everywhere in the book.
This may not seem like a lot of work, but it took me two full weeks to do this.

How to get the new edition?

If you already own the ebook, you get the new edition for free.

If you purchased on, you should have received an email inviting you to download the new edition. If not, search your Inbox for a mail titled “Thank you for your purchase!”; the download link you received should still work.

If you purchased the book on Amazon Kindle, you’d get the new version if you opted for the automatic updates. Otherwise, you must go to Manage Your Content and Devices, and you should see an “update available” button.

If you don’t have the book yet, what are you waiting for? We need your support too! Click on the button below; it only takes a minute.

The paperback version will be available in the fall.

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