Without reading the documentation, the user doesn't even know placeholders/merge fields are a thing.
It'd be best to do those autocomplete, inline tags in the input fields like most modern editor experiences. For example, Yoast SEO does this in their meta title and description fields for placeholders such as the website name or post's title.
If this seems excessive, then add some sort of feature documentation at the very least!
Without reading the documentation, the user doesn't even know placeholders/merge fields are a thing.
It'd be best to do those autocomplete, inline tags in the input fields like most modern editor experiences. For example, Yoast SEO does this in their meta title and description fields for placeholders such as the website name or post's title.
If this seems excessive, then add some sort of feature documentation at the very least!