Thanks for getting in touch about the feature you're looking for!

Although Front doesn't currently offer a visible property such if a message is a template via the API, I hear you and want our Product team to hear this, too. That's why we've recently set up our Product Ideas Portal where you can submit requests for features you need, and what other Front users are looking for. If you see another feature you'd love, just upvote it there and our team will see the tally.

Our Product team reviews these ideas every week. You'll receive an email update if a feature you submit or upvote is developed and shipped.

While not an exact solution, you may consider creating and adding a tag to identify conversations where templates have been used. Tags are visible via the API when fetching a conversation and may help narrow the search. Again, I understand this may not be exactly what you are searching for, but perhaps it could help while a feature request is made. 

We really appreciate your feedback — thank you for taking the time to send it!

- Justin