Open file accepts only *.ino *.pde

Please add load ANY file or at least add *.h *.cpp.

Hi @pju. The Arduino IDE is for working with Arduino sketches. Every Arduino sketch must contain a .ino or .pde file that matches the sketch folder name.

However, you are also welcome to add .h, .cpp, .c, and .S files to the sketch and the Arduino IDE will open these files as well.

You can learn more technical details about Arduino sketches from the Arduino Sketch Specification:
https://arduino.github.io/arduino-cli/latest/sketch-specification/

Sure. It’s to be able to inspect/edit code in libraries folder where is there is no .ino files (excepted example folders).

I would use Notepad++ to do that.

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This is supported. Just right click on any reference, then select “Go to definition” or “Peek” and the source code will be opened, in a separate tab if you used “Go to…”, or in a windowed area if you used “Peek”. A really useful learning tool that is a standard feature in modern advanced IDEs, but previously not available to Arduino users.

Even though you can open the files, they are intentionally made read-only. The reason is that it would be too easy for beginners to unintentionally modify library, core, or toolchain files. That would result in an absolute troubleshooting nightmare.