user-1: My Arduino IDE is not getting started. It just crashes before opening up. I don't know what the problem is. It was working well enough before without any issues. 
This is what I see after running the arduino_debug.exe in the command line

Note: I added a library (DHT) to work with my humidity and temperature sensor and since after then, this issue comes up. I tried to reinstall it like more than 7 times, but the issue still persists.
Please help me with it. Thanks.

user62888: I had the same problem this morning when trying to launch the IDE (1.8.3).
I'm running Linux Mint 18.
Running the IDE from the command line showed the following errors:

The output hints at a problem with 'packages' so I renamed ~/.arduino15/package_index.json to package_index.json.old. The IDE was then able to be launched. 'package_index.json' can then be rebuilt by starting your boards manager through 'Tools->Board'.

user56498: Had same issue when migrating from Arduino IDE 1.8.2 to 1.8.9
In my case, deleting just the library_index.json was not enough but a good hint.
I did also delete the subdirectories of "packages" directory (boards which I downloaded- the ESP32 board and the ESP8266 board), and all files (not folders) in C:\Users\%username%\AppData\Local\Arduino15\ except the preferences.txt
This solved the issue for me.

user26916: The cause of the problem is that you have a corrupted library index file. The solution is to delete the file, which will force the Arduino IDE to download a (hopefully) uncorrupted fresh version from the Internet:

Open the C:\Users\JK\AppData\Local\Arduino15 folder
Delete the file library_index.json
Try starting the Arduino IDE again


For anyone encountering this problem who is using an operating system other than Windows, the location of library_index.json is different:
On Linux:
/home/{username}/.arduino15 (a.k.a. ~/.arduino15)
On macOS:
/Users/{username}/Library/Arduino15
If using the Arduino IDE in portable mode:
{Arduino IDE installation folder}/portable

The issue of a corrupted library index file preventing the Arduino IDE from starting has been reported to the Arduino developers and they are already working on a fix:
https://github.com/arduino/Arduino/issues/7937

-1: <p>My Arduino IDE is not getting started. It just crashes before opening up. I don't know what the problem is. It was working well enough before without any issues. </p>

<p>This is what I see after running the arduino_debug.exe in the command line</p>

<p><a href="https://i.stack.imgur.com/ELFWg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ELFWg.png" alt="enter image description here"></a></p>

<p>Note: I added a library (DHT) to work with my humidity and temperature sensor and since after then, this issue comes up. I tried to reinstall it like more than 7 times, but the issue still persists.</p>

<p>Please help me with it. Thanks.</p>
 62888: <p>I had the same problem this morning when trying to launch the IDE (1.8.3).
I'm running Linux Mint 18.</p>

<p>Running the IDE from the command line showed the following errors:</p>

<p><a href="https://i.stack.imgur.com/1oGPg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1oGPg.png" alt="Arduino IDE 1.8.3 launch errors"></a></p>

<p>The output hints at a problem with 'packages' so I renamed ~/.arduino15/package_index.json to package_index.json.old. The IDE was then able to be launched. 'package_index.json' can then be rebuilt by starting your boards manager through 'Tools->Board'.</p>
 56498: <p>Had same issue when migrating from Arduino IDE 1.8.2 to 1.8.9</p>
<p>In my case, deleting just the library_index.json was not enough but a good hint.</p>
<p>I did also delete the subdirectories of &quot;packages&quot; directory (boards which I downloaded- the ESP32 board and the ESP8266 board), and all files (not folders) in C:\Users\%username%\AppData\Local\Arduino15\ except the preferences.txt</p>
<p>This solved the issue for me.</p>
 26916: <p>The cause of the problem is that you have a corrupted library index file. The solution is to delete the file, which will force the Arduino IDE to download a (hopefully) uncorrupted fresh version from the Internet:</p>

<ol>
<li>Open the C:\Users\JK\AppData\Local\Arduino15 folder</li>
<li>Delete the file library_index.json</li>
<li>Try starting the Arduino IDE again</li>
</ol>

<hr>

<p>For anyone encountering this problem who is using an operating system other than Windows, the location of library_index.json is different:</p>

<p>On Linux:</p>

<p><code>/home/{username}/.arduino15</code> (a.k.a. <code>~/.arduino15</code>)</p>

<p>On macOS:</p>

<p><code>/Users/{username}/Library/Arduino15</code></p>

<p>If using the Arduino IDE in <a href="https://www.arduino.cc/en/Guide/PortableIDE" rel="noreferrer">portable mode</a>:</p>

<p><code>{Arduino IDE installation folder}/portable</code></p>

<hr>

<p>The issue of a corrupted library index file preventing the Arduino IDE from starting has been reported to the Arduino developers and they are already working on a fix:</p>

<p><a href="https://github.com/arduino/Arduino/issues/7937" rel="noreferrer">https://github.com/arduino/Arduino/issues/7937</a></p>
