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Sources of the compile service

As of 14 November 2026

When you compile an Arduino sketch in the code view, our server builds it with the cores, toolchains and libraries below and sends you the firmware. Parts of them are linked into that firmware. Here is each one with its exact version, its licence and where to get its source code at that version.

Licences in your firmware

Your sketch stays your own. Firmware built with LGPL libraries (the Arduino cores, Servo, Adafruit NeoPixel, TM1637, Keyboard …) can be relinked: your sketch and the pinned versions on this page are all it takes to rebuild it, which is what the LGPL asks for when you pass the firmware on.

A GPL-3.0 library (Keypad, the tinyNeoPixel of ATTinyCore) makes firmware that includes it GPL-3.0 when you distribute it: its complete source, your sketch included, then goes with it.

The runtime libraries of GCC come with the GCC Runtime Library Exception: they do not change the licence of your firmware.

This is a list of facts, not legal advice.

Arduino cores

  • Arduino AVR core 1.8.8 – Arduino Uno, Nano, Mega 2560, Leonardo, Pro Micro: the core and its libraries Wire, SPI, EEPROM, SoftwareSerial, HID. Licence: LGPL-2.1-or-later. source at 1.8.8 · archive
  • ATTinyCore (Spence Konde) 1.5.2 – ATtiny85: the core and its libraries Wire, SPI, EEPROM, Servo; its tinyNeoPixel is GPL-3.0. Licence: LGPL-2.1-or-later. source at 1.5.2 · archive
  • Arduino-Pico (Earle F. Philhower III) 6.3.2 – Raspberry Pi Pico, Pico W: the core with the Raspberry Pi Pico SDK (BSD-3-Clause), lwIP (BSD-3-Clause) and, for the Pico W, the cyw43 driver (licensed by Raspberry Pi for use with its chips). Licence: LGPL-2.1-or-later. source at 6.3.2 · archive

Compilers and C libraries

  • avr-gcc (GCC 7.3.0, Atmel toolchain 3.6.1, Arduino build 7) 7.3.0-atmel3.6.1-arduino7 – linked: libgcc (runtime library: the GCC exception keeps your firmware free of the GPL). Licence: GPL-3.0-or-later WITH GCC-exception-3.1. source at 7.3.0-atmel3.6.1-arduino7 · archive
  • avr-libc (Atmel toolchain 3.6.1) 2.0.0-atmel3.6.1 – linked: the C library and the device headers. Licence: BSD-3-Clause. source at 2.0.0-atmel3.6.1 · archive
  • pico-quick-toolchain (arm-none-eabi GCC with newlib) 5.0.0 – linked: libgcc, libstdc++ (GCC exception) and newlib (BSD-style licences). Licence: GPL-3.0-or-later WITH GCC-exception-3.1. source at 5.0.0 · archive

Libraries for your sketches

Only the libraries your sketch includes end up in its firmware.

If a link stops working

The links point to the upstream projects at the tag of each version and to the archives the build installs. If one of them is gone, write to hello@deckle.io and we send you the source of the version we used.