# Template Interpolation Key Usage

**URL:** https://meta.discourse.org/t/template-interpolation-key-usage/135609
**Category:** Support
**Created:** [December 10, 2019, 11:44pm UTC](https://meta.discourse.org/t/template-interpolation-key-usage/135609 "2019-12-10T23:44:11Z")
**Posts on this page:** 3
**Page:** 1

<div class="post-metadata">

### Author: ![kimardenmiller](https://sea3.discourse-cdn.com/meta/user_avatar/meta.discourse.org/kimardenmiller/32/119631_2.png) [@kimardenmiller](https://meta.discourse.org/u/kimardenmiller)
#### Post date: [December 10, 2019, 11:44pm UTC](https://meta.discourse.org/t/template-interpolation-key-usage/135609/1 "2019-12-10T23:44:11Z")

</div>

[Related to this post](https://meta.discourse.org/t/invalid-interpolation-key/87944), we previously customized templates such as `user_notifications.reply_by_email`, e.g. to say …

- Visit Topic or reply to this email to respond.
- Reply with a private message

The second item has the link:

```
%{base_url}/new-message?username=%{username}&title=Your%20post%20%{topic_title_url_encoded}&body=Regarding%20your%20post%20in%20%{base_url}%{url}

```

This has been in use for some time and works perfectly. Today we need to change the text in `user_notifications.reply_by_email`, but on saving get the error:

```
The following interpolation key(s) are invalid: "username, topic_title_url_encoded"

```

Why the limitation now, and how can we get around it?

---

<div class="post-metadata">

### Author: ![system](https://sea3.discourse-cdn.com/meta/user_avatar/meta.discourse.org/system/32/443519_2.png) [@system](https://meta.discourse.org/u/system)
#### Post date: [September 21, 2023, 4:02am UTC](https://meta.discourse.org/t/template-interpolation-key-usage/135609/2 "2023-09-21T04:02:51Z")

</div>



---

<div class="post-metadata">

### Author: ![simon](https://sea3.discourse-cdn.com/meta/user_avatar/meta.discourse.org/simon/32/339122_2.png) [@simon](https://meta.discourse.org/u/simon)
#### Post date: [September 21, 2023, 4:11am UTC](https://meta.discourse.org/t/template-interpolation-key-usage/135609/3 "2023-09-21T04:11:09Z")

</div>

> [@kimardenmiller](#):
>
> Why the limitation now, and how can we get around it?

Thankfully, this is now documented here: [Interpolation Keys for Customizing Text and System Email Templates](https://meta.discourse.org/t/interpolation-keys-for-customizing-text-and-email-templates/264604).