Serialize to JSON: tojson

The tojson filter converts a Python object (like a dictionary, list, string, or number) into a JSON-formatted string. This is a Home Assistant override of the standard tojson filter. It accepts an optional indent parameter to pretty-print the output with indentation.

This filter is useful when you need to produce JSON output for external services or for debugging. If you need more control over the serialization (such as sorting keys or controlling ASCII escaping), consider using the to_json filter instead, which offers additional options.

Usage

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

{{ {"temperature": 21.5, "unit": "C"} | tojson }}

{"temperature": 21.5, "unit": "C"}

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 | tojson(
    indent: int | None = None,
) -> str

Function parameters

The following parameters can be provided to this filter.

Pretty-printed output

Use the indent parameter to format the JSON with indentation for readability.

{{ {"name": "Living Room", "temperature": 21.5} | tojson(indent=2) }}

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

Good to know

• The default output includes a space after each comma and colon, unlike to_json, which produces a compact string.
• If you need sorted keys or control over ASCII escaping, use to_json instead.

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.

Send a JSON payload via MQTT

Build a dictionary from sensorSensors return information about a thing, for instance the level of water in a tank. [Learn more] values and serialize it for an MQTT publish action.

action:
  - action: mqtt.publish
    data:
      topic: "home/sensors"
      payload: >
        {{
          {
            "temperature": states("sensor.temperature") | float,
            "humidity": states("sensor.humidity") | float
          } | tojson
        }}

Serialize a list

Convert a list of values to a JSON array string.

{{ ["on", "off", "on"] | tojson }}

["on", "off", "on"]

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:

• Serialize to JSON: to_json - Serializes a value to a JSON string.

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