# Expression as parameter in UDT

**URL:** <https://forum.inductiveautomation.com/t/expression-as-parameter-in-udt/113892>\
**Category:** General Discussion\
**Created:** [February 11, 2026, 5:44am UTC](https://forum.inductiveautomation.com/t/expression-as-parameter-in-udt/113892 "2026-02-11T05:44:28Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Eric\_White](https://avatars.discourse-cdn.com/v4/letter/e/85e7bf/32.png) [@Eric\_White](https://forum.inductiveautomation.com/u/Eric_White)\
**Post date:** [February 11, 2026, 5:44am UTC](https://forum.inductiveautomation.com/t/expression-as-parameter-in-udt/113892/1 "2026-02-11T05:44:28Z")

</div>

Curious has anyone passed a parameter into a UDT which is an expression. Then have an expression tag execute it. Typically, the expression tag just returns the parameter as a string.  
I see quite a few posts asking about this which either fade away without much response or end with someone suggesting tag().

I found a work around where if you export the UDT config, and update the expression field using a text editor to be like below, it works.

"expression": {"bindType":"parameter","binding","{expressionParam}"}

(where expressionParam is a UDT parameter which contains the expression as a string)

In my example, I was using a few relative tag paths in expressionParam, and it also saves having to multiple parameters and or using the tag() function.

ie replace 'tag(param1) + tag(param2)' with '{[.]tag1} + {[.]tag2}'

I currently see 2 negatives with this work around. Wondering if there are any more pros/cons to consider before I start using it properly:

- When you open the UDT in Ignition, there is no visibility on the changes made in text editor. The expression field of the tag is **blank.** But it does correctly run the expression defined in expressionParam. Its not great for visibility, but I could include something in the Meta Data/Documentation I guess.

- To me this seems a bit of a ‘hack’, so I assume probably not encouraged/supported by IA. Is it something I should avoid using in case IA see it as a security issue and block it in future releases (currently v8.1.48).

---

<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [February 11, 2026, 2:04pm UTC](https://forum.inductiveautomation.com/t/expression-as-parameter-in-udt/113892/2 "2026-02-11T14:04:15Z")

</div>

You can use `system.tag.configure()` to assign an expression using a dictionary with the binding details. Passing through a UDT parameter is unlikely to work.

---

<div class="post-metadata">

**Author:** ![Eric\_White](https://avatars.discourse-cdn.com/v4/letter/e/85e7bf/32.png) [@Eric\_White](https://forum.inductiveautomation.com/u/Eric_White)\
**Post date:** [February 11, 2026, 10:53pm UTC](https://forum.inductiveautomation.com/t/expression-as-parameter-in-udt/113892/3 "2026-02-11T22:53:34Z")

</div>

> [@pturmel](#):
>
> Passing through a UDT parameter is unlikely to work

That’s why I’m unsure if I should continue pursuing this or not. It does seem to work, but maybe it’s not supposed to? That or I didn’t understand your reply.

UDT Instance

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/6/4/64624c875417e6ee3ae9b20da5a65aea6446f429.png)

UDT Definition

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/2/d/2de3069df674a2f24a62bec2a05c5a5b0a4fd6ea.png)

I fully understand I can do this in other ways, and I probably will end up doing one of those ways, mainly because the binding is hidden from the popup tag editor. But also, it would be nice if it was a UDT like this, so it was closer aligned with my other tag structures.

---

<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [February 11, 2026, 11:09pm UTC](https://forum.inductiveautomation.com/t/expression-as-parameter-in-udt/113892/4 "2026-02-11T23:09:58Z")

</div>

> [@Eric\_White](#):
>
> It does seem to work

Hmmm. I didn't **expect** it to work. Not the first time that Ignition has surprised me in a good way. Carry on. 😁