Serialize to JSON: tojson

The tojson filter converts a value (like a dictionary, list, string, or number) into a JSON-formatted string. This is the standard tojson filter from Jinja. 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 output, use the to_json filter instead. It offers additional options, such as keeping special characters as they are.

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 = are usually required. A few optional parameters have no default value, so the signature shows them without a = as well. To check whether a parameter is required, look at the parameter list below the signature. Each parameter is marked as Required or Optional.

The most common optional parameter without a default value is default. The default parameter sets the value a function returns when the function can’t produce a result, for example, when float gets text that isn’t a number. If you leave out default, there is no fallback value, so most functions raise an error and the template fails. The parameter list of each function says what happens. If you set default, the function returns your value instead.

round(
    value: Any,
    precision: int = 0,
    method: str = "common",
    default: Any,
) -> float | int | Any

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.
• The keys of a dictionary are always sorted alphabetically.
• Some characters are escaped: <, >, &, and ' become \u003c, \u003e, \u0026, and \u0027. This makes the output safe to place in HTML text, in a <script> element, or in an HTML attribute with single quotes. Double quotes aren’t escaped, so don’t place the output in an attribute with double quotes.
• Characters outside the ASCII range are escaped too. For example, °C becomes \u00b0C. To keep these characters as they are, use to_json.
• Date and time values and state objects can’t be converted. They cause an error.

Try it yourself

Ready to test this? Open Settings > 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.