Serialize to JSON: to_json

The to_json filter converts a Python object (like a dictionary, list, string, or number) into a JSON-formatted string. This is the opposite of from_json, which parses a JSON string back into an object.

This is essential when you need to send structured data to external services. Many integrations like MQTT, REST, and webhooks expect JSON-formatted payloads. For example, you might build a dictionary with sensor data and convert it to JSON for an MQTT publish, or format a payload for a REST API call. The optional parameters let you control the output format: pretty_print adds indentation for readability, sort_keys orders the keys alphabetically, and ensure_ascii escapes non-ASCII characters.

Usage

Here’s how to use this template function. Copy any example and adjust it to your setup.

{{ {"temperature": 21.5, "humidity": 45} | to_json }}

{"temperature":21.5,"humidity":45}

Function signature

The signature is a technical summary of this template function. It shows the name of the function, the values (called parameters) it accepts, and what type of data each parameter expects (for example, a piece of text or a number).

Function parameters that have a = with a value after them are optional. If you leave them out, the default value shown is used automatically. Function parameters without a default are required.

value | to_json(
    ensure_ascii: bool = False,
    pretty_print: bool = False,
    sort_keys: bool = False,
) -> str

Function parameters

The following parameters can be provided to this filter.

Pretty-printed output

Use pretty_print to format the JSON with indentation, making it easier to read in logs or on dashboards.

{{
  {"name": "Living Room", "temperature": 21.5}
  | to_json(pretty_print=true)
}}

{
  "name": "Living Room",
  "temperature": 21.5
}

Good to know

• The output has no spaces between keys and values by default, which is ideal for MQTT or API payloads but less readable. Turn on pretty_print for debugging.
• Values that are not JSON-serializable (like datetime objects) raise an error. Convert them to strings or numbers first.
• Dictionary keys are preserved in their original order unless you set sort_keys=true.

Try it yourself

Ready to test this? Open Developer tools > Template, paste the example into the Template editor, and watch the result update on the right. Edit the values to see how the function adapts to your own entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this function comes up in automations and templates. Copy any example and adapt it to your setup.

Publish sensor data via MQTT

Build a JSON payload from sensor values and publish it to an MQTT topic.

action:
  - action: mqtt.publish
    data:
      topic: "home/sensors/living_room"
      payload: >
        {{
          {
            "temperature": states("sensor.living_room_temperature") | float,
            "humidity": states("sensor.living_room_humidity") | float,
            "timestamp": now() | as_timestamp | int
          } | to_json
        }}

Send data to a REST API

Format a dictionary as JSON for a RESTful notification or webhook.

action:
  - action: rest_command.send_data
    data:
      payload: >
        {{
          {
            "event": "door_opened",
            "entity": "binary_sensor.front_door",
            "state": states("binary_sensor.front_door")
          } | to_json
        }}

Sort keys for consistent output

Use sort_keys when you need deterministic output, for example when comparing JSON strings.

{{ {"z": 1, "a": 2, "m": 3} | to_json(sort_keys=true) }}

{"a":2,"m":3,"z":1}

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with your template and expected result, or share on our subreddit /r/homeassistant.

Related template functions

These functions work well alongside this one:

• Parse JSON string: from_json - Parses a JSON string into a Python object.

• Merge dictionaries: combine - Merges multiple dictionaries into one.