Web Server API

Since version 1.3, ESPHome includes a built-in web server that can be used to view states and send commands. In addition to the web-frontend available under the root index of the web server, there’s also two other features the web server currently offers: A real time event source and REST API.

Note that the web server is only and will only ever be intended to view and edit states. Specifically not something like configuring the node, as that would quickly blow up the required flash and memory size.

First up, to use the web server enable it using App.init_web_server() directly from code or using the Web Server Section in ESPHome. Then, navigate to the front end interface with the IP of the node or alternatively using mDNS with <name>.local/. So for example to navigate to the web server of a node called livingroom, you would enter livingroom.local/ in your browser.

While it’s currently recommended to use ESPHome directly through Home Assistant, if you want to integrate ESPHome with an external or self-built application you can use two available APIs: the real-time event source API and REST API.

Event Source API

If you want to receive real-time updates for sensor state updates, it’s recommended to use the Event Source Web API. With the URL /events, you can create an Event Source that receives real-time updates of states and the debug log using server-sent events. Event sources are easy to implement in many languages and already have many libraries available. For example eventsource for node.js and eventsource for python.

Currently, there are three types of events sent: ping, state and log. The first one is repeatedly sent out to keep the connection alive. log events are sent every time a log message is triggered and is used to show the debug log on the index page. state is where the real magic happens. All events with this type have a JSON payload that describes the state of a component. Each of these JSON payloads have two mandatory fields: id and state. ID is the unique identifier of the component and is prefixed with the domain of the component, for example sensor. state contains a simple text-based representation of the state of the underlying component, for example ON/OFF or 21.4 °C. Several components also have additional fields in this payload, for example lights have a brightness attribute.

../_images/event-source.png

Example payload of the event source API.

Additionally, each time a client connects to the event source the server sends out all current states so that the client can catch up with reality.

The payloads of these state events are also the same as the payloads of the REST API GET calls. I would recommend just opening the network debug panel of your web browser to see what’s sent.

REST API

There’s also a simple REST API available which can be used to get and set the current state. All calls to this API follow the URL schema /<domain>/<id>[/<method>?<param>=<value>]. The domain is the type of the component, for example sensor or light. id refers to the id of the component - this ID is created by taking the name of the component, stripping out all non-alphanumeric characters, making everything lowercase and replacing all spaces by underscores. To confirm the <id> to use, you can set the log level to VERY_VERBOSE and check the object_id: in the logs.

By creating a simple GET request for a URL of the form /<domain>/<id> you will get a JSON payload describing the current state of the component. This payload is equivalent to the ones sent by the event source API.

To actually control the state of a component you need to send a POST request with a method like turn_on. For example, to turn on a light, you would send a POST request to /light/livingroom_lights/turn_on. Some components also optionally accept URL parameters to control some other aspects of a component, for example the brightness of a light.

Sensor

Sensors only support GET requests by sending a request to /sensor/<id>. For example sending a GET request to /sensor/outside_temperature could yield this payload:

{
  "id": "sensor-outside_temperature",
  "state": "19.8 °C",
  "value": 19.76666
}
  • id: The id of the sensor. Prefixed by sensor-.

  • state: The text-based state of the sensor as a string.

  • value: The floating point (filtered) value of the sensor.

Binary Sensor

Binary sensors have a similar payload and also only support GET requests. For example requesting the current state of a binary sensor using the URL binary_sensor/living_room_status could result in following payload:

{
  "id": "binary_sensor-living_room_status",
  "state": "ON",
  "value": true
}
  • id: The id of the binary sensor. Prefixed by binary_sensor-.

  • state: The text-based state of the binary sensor as a string.

  • value: The binary (true/false) state of the binary sensor.

Switch

Switches have the exact same properties as a binary sensor in the state reporting aspect, but they additionally support setting states with the turn_on, turn_off and toggle methods.

Each of these is quite self explanatory. Creating a POST request to /switch/dehumidifier/turn_on would for example result in the component called “Dehumidifier” to be turned on. The server will respond with a 200 OK HTTP return code if the call succeeded.

Light

Lights support quite a few more complicated options, like brightness or color. But first, to get the state of a light, send a GET request to /light/<id>, for example light/living_room_lights.

{
  "id": "light-living_room_lights",
  "state": "ON",
  "brightness": 255,
  "color": {
    "r": 255,
    "g": 255,
    "b": 255
  },
  "effect": "None",
  "white_value": 255
}
  • id: The id of the light. Prefixed by light-.

  • state: The text-based state of the light as a string.

  • brightness: The brightness of the light from 0 to 255. Only if the light supports brightness. If state is OFF, this can still report values like 255 in order to send the full state.

  • color: The color of this light, only if it supports color.

    • r: The red channel of this light. From 0 to 255.

    • g: The green channel of this light. From 0 to 255.

    • b: The blue channel of this light. From 0 to 255.

  • effect: The currently active effect, only if the light supports effects.

  • white_value: The white value of RGBW lights. From 0 to 255. Only if the light supports white value.

  • color_temp: The color temperature of the RGBWW light. Between minimum mireds and maximum mireds of the light. Only if the light support color temperature.

Setting light state can happen through three POST method calls: turn_on, turn_off and toggle. Turn on and off have additional URL encoded parameters that can be used to set other properties. For example creating a POST request at /light/<id>/turn_on?brightness=128&transition=2 will create transition with length 2s to the brightness 128 while retaining the color of the light.

turn_on optional URL parameters:

  • brightness: The brightness of the light, from 0 to 255.

  • r: The red color channel of the light, from 0 to 255.

  • g: The green color channel of the light, from 0 to 255.

  • b: The blue color channel of the light, from 0 to 255.

  • white_value: The white channel of RGBW lights, from 0 to 255.

  • flash: Flash the color provided by the other properties for a duration in seconds.

  • transition: Transition to the specified color values in this duration in seconds.

  • effect: Set an effect for the light.

turn_off optional URL parameters:

  • transition: Transition to off in this duration in seconds.

Fan

Fans are similar to switches as they can be turned on/off and toggled. In addition, if the underlying fan supports it, fans in the web server also support the speed settings “low”, “medium” and “high” and an oscillation setting. To get the current state of a fan, create a GET request to /fan/<id>.

{
  "id": "fan-living_room_fan",
  "state": "ON",
  "value": true,
  "speed_level": 2,
  "oscillation": false
}
  • id: The id of the fan. Prefixed by fan-.

  • state: The text-based state of the fan as a string.

  • value: The binary (true/false) state of the fan.

  • speed_level: The speed level of the fan if it’s supported. Value is between 1 and the maximum supported by the fan.

  • oscillation: Whether the oscillation setting of the fan is on. Only sent if the fan supports it.

To control the state of the fan, send POST requests to /fan/<id>/turn_on, /fan/<id>/turn_off and /fan/<id>/toggle. Turn on additionally supports these optional parameters:

  • speed_level: The new speed level of the fan. Values as above.

  • oscillation: The new oscillation setting of the fan. Values as above.

Cover

Covers are again similar to switches whose two possible states are OPEN and CLOSED. They can however be in an intermediate position, anywhere between 0.0 (fully closed) to 1.0 (fully open). They usually take some time to move from one position to another and can also be stopped midway. An example GET request for /cover/front_window_blinds might return:

{
  "id": "cover-front_window_blinds",
  "state": "OPEN",
  "value": 0.8,
  "current_operation": "IDLE",
  "tilt": 0.5
}
  • id: The ID of the cover, prefixed with cover-.

  • state: OPEN or CLOSED. Any position other than 0.0 is considered open.

  • value: Current cover position as a float number.

  • current_operation: OPENING, CLOSING or IDLE.

  • tilt: (only if supported by this cover component) tilt angle from 0.0 to 1.0.

POST requests on the other hand allow performing actions on the cover, the available methods being open, close, stop and set. The following parameters can be used:

  • position: The target position for a set call. The open method implies a target position of 1.0, close implies a target position of 0.0.

  • tilt: The tilt angle to set, if supported.

Creating a POST request to /cover/front_window_blinds/set?position=0.1&tilt=0.3 will start moving the blinds towards an almost completely closed position and a new tilt angle.