Basic requirements for developing applications

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  Debug Mode: Your device must be debuggable. Normally it is sufficient to dial the debug code *#*#33284#*#* (on Qualcomm), or in addition *#*#0574#*#* (Spreadtrum) to enable the USB debugging.
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  ADB and Fastboot: Android Debug Bridge, aka ADB, is a command line with which you can explore, perform actions and make changes to an Android or a KaiOS device. Fastboot is a diagnostic protocol primarily used to modify the flash filesystem via USB connection from the host computer.
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  WebIDE, or other DevTools WEBIDE is the most common and complete of development tools. For KaiOS 2.5 and lower, choose an old version of Firefox (59 or earlier) or Pale Moon (28.6.1 or earlier), or use the official Kaios emulator (KaiOSRT).