Add-default-to-from-json (#39405)

source/_docs/configuration/templating.markdown

@@ -903,6 +903,29 @@ The temperature is 25°C
 
 {% endraw %}
 
+`from_json(default)` function will attempt to convert the input to `json`. If that fails, returns the `default` value, or if omitted raises an error.
+
+#### Template
+
+{% raw %}
+
+```text
+{% set result = 'not json'|from_json('not json') %}
+The value is {{ result }}
+```
+
+{% endraw %}
+
+#### Output
+
+{% raw %}
+
+```text
+The value is not json
+```
+
+{% endraw %}
+
 ### Is defined
 
 Sometimes a template should only return if a value or object is defined, if not, the supplied default value should be returned. This can be useful to validate a JSON payload.