Typical use case

Homie for ESP8266 lets you implement custom settings that can be set from the JSON configuration file and the Configuration API. Below is an example of how to use this feature:

HomieSetting<long> percentageSetting("percentage", "A simple percentage");  // id, description

void setup() {
  percentageSetting.setDefaultValue(50).setValidator([] (long candidate) {
    return (candidate >= 0) && (candidate <= 100);


setDefaultValue() before Homie.setup()

As shown in the example above, the default value has to be set before Homie.setup() is called. Otherwise you get an error on startup if there is also no value configured in JSON configuration file.

An HomieSetting instance can be of the following types:

Type Value
bool true or false
long An integer from -2,147,483,648 to 2,147,483,647
double A floating number that can fit into a real64_t
const char* Any string

By default, a setting is mandatory (you have to set it in the configuration file). If you give it a default value with setDefaultValue(), the setting becomes optional. You can validate a setting by giving a validator function to setValidator(). To get the setting from your code, use get(). To get whether the value returned is the optional one or the one provided, use wasProvided().

For this example, if you want to provide the percentage setting, you will have to put in your configuration file:

  "settings": {
    "percentage": 75

Updating custom settings

In order to change custom settings send via MQTT the JSON Object to: homie/<device>/$implementation/config/set. The JSON object might include all settings you need to update at once. As well, partial/incremental update is supported. JSON object should be flat string. From the example above it becomes: {"settings":{"percentage":75}}

!!! tip Updated custom settings are saved to SPIFFS automatically.

Once you updated the custom settings Homie will save it to the Flash and reboot itself. The reboot causes the updated and stored setting be read into RAM and be used in actual code.

!!! tip If function of your Homie device is sensitive to reboots, then consider other method of custom settings.

Sometimes, the device is designed for non-interrupted service. So the reset by setting update is not acceptable and can affect the device function/behavior.


See the following example for a concrete use case:

GitHub logo CustomSettings.ino