Fastboot from Android without a PC

NekoFlash lets one Android phone or tablet act as the USB host for a second Android device in Fastboot mode. This removes the desktop computer from the transport path, but it does not remove the normal Fastboot safety requirements.

Requirements

• Android 8.0 / API 26 or newer on the NekoFlash host device.
• USB Host / OTG support.
• A data-capable USB OTG or USB-C cable.
• The target device already booted into Fastboot / bootloader mode.
• Device-specific firmware or images that match the exact model and partition layout.

1. Connect and verify the target

Connect the target to the NekoFlash host and wait for the USB session to attach. With USB-C to USB-C, Android can sometimes negotiate the wrong power or data role. The NekoFlash phone should act as the host and the intended target should appear as the connected USB device.

Do not start a flash, erase, format or slot-changing operation when the detected device is not clearly the intended target.

2. Start with non-destructive diagnostics

Before changing storage, use Fastboot diagnostics such as device variables and partition/slot discovery. NekoFlash can query getvar data and build a partition inventory from the connected bootloader.

This is especially important on A/B devices, where a partition may have _a and _b slots or may be managed through a logical/dynamic partition layout.

3. Treat writes as device-specific operations

NekoFlash supports Fastboot operations such as flash, boot, erase, format, set_active and supported OEM/flashing commands. Support at the protocol level does not mean every command is appropriate for every device.

For large Fastboot DATA transfers, NekoFlash deliberately avoids automatic retry when the peer may have consumed an unknown prefix of a payload. This prevents a seemingly convenient retry from hiding an ambiguous mid-stream write state.

When to stop

Stop before writing if the model, slot, partition name, image origin or target mode is uncertain. Reconnect or re-enter Fastboot if the USB role is wrong or the session is unstable.