Creating a custom envelope

Envelopes are Toit's way of packaging the native firmware and Toit containers together. After going through an extraction process, this is what is flashed to devices.

Envelopes are designed to be modified, so that Toit containers can be added or removed from them. This approach makes it possible to download precompiled envelopes, where the native firmware has been built for you, and then add your own Toit containers to them.

Toit already provides multiple envelopes at the envelopes repository. However, if you need a different configuration of the native firmware, then you might need to create your own custom envelope.

This tutorial will show you how to create a custom envelope.


Contrary to almost all other tutorials, this tutorial requires to compile C/C++ code. This means that you need to have a full build environment installed. See the Toitlang's build instructions for more information.


To make it easier to create a custom envelope, we have created a template that you can use. The template is available at the custom envelope template repository.

The template repository is optimized for macOS and Linux. If you are using Windows, you might need to adjust some of the scripts.

The following instructions summarize GitHub's cloning instructions to duplicate the repository.

Start by creating a fresh repository on GitHub. Then run the following commands, replacing your-owner/your-repo with the name of your repository:

git clone --bare
cd template-custom-envelope.git
git push --mirror
cd ..
rm -rf template-custom-envelope.git
cd your-repo

Configuring the template

As the README of the template repository explains, you need to configure the template to match your needs. For this tutorial we assume that you are using an ESP32 (the default), and that you will modify license, and the CI action at a later point. We will also keep the echo-service in the components directory, for now. You should remove it if you don't need it. See the c-service tutorial for more information.

Update the toit SDK to your preferred version, and then initialize the submodules. The SDK version you want depends on your needs. If you want to use an installed Jaguar, you should use the same SDK version as Jaguar uses. You can find its SDK version by running jag version. Once you know the version run the following commands:

pushd toit
git checkout YOUR_VERSION
git submodule update --init --recursive

Toit snapshots are only compatible with the SDK version they were compiled with. Always make sure that the SDK version in the template matches the SDK version you are using.

Run the init step, which will copy some files from the Toit repository:

make init

Changing the sdkconfig

The most common reason to create a custom envelope is to change the sdkconfig file. This file is used by the ESP-IDF build system to configure the native firmware.

To change the sdkconfig file, you can run:

make menuconfig

This will open a menu where you can change the configuration. For example, you can disable Bluetooth support (to save memory and space), or change the default name of the device. Use '/' to search for a specific configuration. The bluetooth configuration would be BT_ENABLED, and the device name LWIP_LOCAL_HOSTNAME (for network) and CONFIG_BT_NIMBLE_SVC_GAP_DEVICE_NAME for Bluetooth.

When you are done, save the configuration and exit the menu. This will trigger an automatic creation of sdkconfig.defaults. We recommend to commit both files (sdkconfig and sdkconfig.defaults) to your repository.

Running make diff you should now see your changes compared to the default configuration of a Toit envelope.


To build the custom envelope, run:


This will first build the Toit SDK for your platform, and then build the native firmware. The result is an firmware.envelope file in the build/esp32 directory.


If you have Jaguar installed, you can flash the envelope to your device by running the following command:

jag flash build/esp32/firmware.envelope


You can add containers to the envelope and then flash it, or use it for OTA updates.

We recommend to copy the envelope to a different name, so that you can keep the original envelope as a empty starting point. The toit executable can be found in build/host/sdk/bin.

cp build/esp32/firmware.envelope my-envelope.envelope
toit compile --snapshot -o hello.snapshot hello.toit
toit tool firmware -e firmware-esp32 container install hello hello.snapshot


Use the firmware tool to flash the envelope to your device. Adjust the port to your device's port. The toit executable can be found in build/host/sdk/bin:

toit tool firmware -e my-envelope.envelope flash --port /dev/ttyUSB0

GitHub action

The template repository comes with a GitHub action that builds the envelope. You can adjust it, so that it uploads the created envelope to a release.

We recommend to include the SDK version in the release name, so that you can easily find the correct envelope for a specific SDK version.


This tutorial showed how to create a custom envelope. The template repository provides a good starting point, and you can adjust it to your needs.