What causes error downloading https://downloads.arduino.cc/libraries/library_index.json?

I have two portable "installations" of the Arduino-IDE on my laptop

Arduino 1.8.13 and 1.8.16
the 1.8.16 shows an error-message
error downloading https://downloads.arduino.cc/library_index.json

thank you J-M-L the correct URL is
https://downloads.arduino.cc/libraries/library_index.json

while the 1.8.13-version can download it.
I'm not aware of having changed something in my 1.8.16-version.
what can cause this error ? What do I have to check to fix it?

best regards Stefan

the file linked ( https://downloads.arduino.cc/library_index.json) contains this

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title>File Not Found</title>
    </head>
    <body>
        <pre>
     _                     _                 _                       _       _                         
    | |                   | |               | |                     | |     (_)                        
  __| | _____      ___ __ | | ___   __ _  __| |___      __ _ _ __ __| |_   _ _ _ __   ___      ___ ___ 
 / _` |/ _ \ \ /\ / | '_ \| |/ _ \ / _` |/ _` / __|    / _` | '__/ _` | | | | | '_ \ / _ \    / __/ __|
| (_| | (_) \ V  V /| | | | | (_) | (_| | (_| \__ \_  | (_| | | | (_| | |_| | | | | | (_) |  | (_| (__ 
 \__,_|\___/ \_/\_/ |_| |_|_|\___/ \__,_|\__,_|___(_)  \__,_|_|  \__,_|\__,_|_|_| |_|\___/  (_\___\___|
                                                                                                       
                                                                                                       
        </pre>
    </body>
</html>  

it does not look like JSON at all... (or there is some smart redirect when not accessed from the IDE)

fascinating! (as Mr. Spock would say)

But why the heck does it work with my Arduino 1.8.13-portable and a freshly installed Arduino 1.8.16-portable version?

I mean in the 1.8.13-portable and the new 1.8.16-portable I click on manage libraries and downloading works?!

best regards Stefan

there might be some wizardry done on the HTTP side and some smart redirect when not accessed from the IDE.

if you have a way to inspect traffic, then look at what the IDE is really doing

BTW, was already discussed in the past (but no clear solution)

ah, you possibly got the URL wrong it should be

https://downloads.arduino.cc/libraries/library_index.json

not

https://downloads.arduino.cc/library_index.json

@J-M-L thank you for pointing out that.
My fault of wrong re-typing the path in my initial posting here is a screenshot
which I should have posted immetiately.

As you can see the URL is correct. Anyway with my old 1.8.16-portable version I get this error

best regards Stefan

I'm trying to narrow down the problem through copying the subfolders from the old 1.8.16-portable to the new 1.8.16-portable
After copying all subfolders of "portable" the new installed 1.8.16-portable can still donwload this library_index.json.
grafik
though the boards are not all there.

I guess I have to run the board-manager again?
Or do I have to copy some other folders which are above the "portable"-folder??

best regards Stefan

I'm not a windows user... Might be permissions issues or the like.

Hi
What links are there in your IDE at:

Files --->> Preferences --->> Additional Boards Manager URLs:

in both IDEs ( 1.8.13 and 1.8.16)?

RV - mineirin

They are the same
13: https://dl.espressif.com/dl/package_esp32_index.json, http://arduino.esp8266.com/stable/package_esp8266com_index.json, https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json

16: https://dl.espressif.com/dl/package_esp32_index.json, http://arduino.esp8266.com/stable/package_esp8266com_index.json, https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json

Well after copying all the package_seeeduino_boards_index.json package-index.json-files

ESPs and Seeduino XIAO works again. Only Teensy does not appear.

What is not yet working is the color of the opened tabs
Where can I adjust the color of the tabs at the top of the IDE-window?

grafik

This is a completely different problem than the initial problem I started the thread with.
So here is a link to this tab-text-color-problem-thread

best regards Stefan