Writing for interfaces: metrics and KPIs for those just starting out

If you're just getting interested in interface writing, you've probably heard that "words matter." The natural question next is: how do I know if a text is working?

This is exactly the right question. Most people who work with products decide on the text on a screen on instinct, "I think it'll be clearer this way", and never check to see if it is. The result is that writing becomes personal taste, and personal taste is difficult to defend and impossible to improve consistently.

The central idea of this text is encouraging for those just starting out: interface writing can be measured. You don't need expensive tools or advanced statistics to get started. You need to understand what to observe, and that's what we're going to break down.

What is, after all, "writing for interfaces"

Writing for interfaces, or UX writing, is all the text that appears inside a digital product and guides the person to do something: the name of a button, the instruction of a form, the error message, the text of an empty screen, the confirmation after an action.

Unlike an article or a marketing piece, this text does not exist to be appreciated. It exists to function. A perfectly written button is one that a person understands without thinking and clicks without hesitation.

Therefore, the way of evaluating is different. You don't ask "is this text beautiful?" The question is “did this text make the person understand and act?” This question change is the beginning of everything.

Why measure, and not just give an opinion

When two people disagree about a text, without data, the argument is won by the person with more position or more conviction. This doesn't improve the product, it just decides who is in charge.

Measuring takes the decision out of the realm of opinion. If you change the text on a button and more people start clicking, you have an answer. It doesn't matter who thought what; the user responded.

For those who are learning, this is the most valuable habit to build: treating each text as a hypothesis that can be verified, and not as a truth defined at the time it was written. This mentality applies to your entire career.

The basic metrics you can track

You don't need to start with a lot of metrics. Start with a few, well-understood ones.

Click or completion rate. The simplest. Of every hundred people who see a button or start a flow, how many complete it? If you change the text and this number goes up, writing has improved communication.

Form errors. Notice where people make mistakes when filling out fields. Often the problem is not the person, it is the instruction that did not make clear what was expected.

Repeated questions. If the same questions reach support or comments, it is a sign that the interface did not explain that point well. This is one of the easiest signals to capture when you don't yet have sophisticated tools.

Abandonment at a specific step. When a lot of people give up at the same point in a flow, it's worth looking at what the text is asking there. Sometimes a word scared, confused or seemed to require too much effort.

These four already give an honest overview. The secret is not the number of metrics, but looking at them with the right question: what is the text on this screen causing?

A first experiment, in practice

The best way to learn is to do. Choose a simple screen, a button, an error message, and propose an alternative version of the text.

Imagine a button that says "Submit". Few people click. You test "I want to receive the quote" and more people come forward. The difference is not magical: the second version says what the person will gain, instead of describing a generic action.

This is the kind of test that teaches you more than any book. You formulate a hypothesis ("a text that shows the benefit converts more"), compare and observe the result. Start small, with something low risk, and build confidence.

Common mistakes made by those just starting out

The first mistake is wanting to measure everything at once and drowning in numbers. Start with a metric and a canvas. Depth comes with time.

The second is to confuse coincidence with cause. If conversion went up in the same week that you changed the text, maybe it was the text, or maybe it was a promotion that ran along with it. When possible, change one thing at a time so you know who to give credit to.

The third is to forget the context. A text that works for one audience may fail with another. In Brazil, this is important: tone, formality and vocabulary change a lot depending on who is on the other side. Writing for a banking application is not like writing for a municipal public service used by the entire population.

Where to find text to improve first

When you decide to practice, the question arises: where to start within a product full of screens? There are some places where writing tends to attract more attention, and it's worth prioritizing them.

Error messages are a great starting point. They appear at the user's moment of greatest frustration, and are usually written hastily, in technical language that no one understands. "Error 400" doesn't help anyone; "the email entered does not seem valid, check if there is an at sign" solves the problem.

Empty screens are another forgotten place. When a list has nothing yet, many products only show blank space. It's a missed opportunity to explain what that screen does and how to start using it.

And the action buttons, of course. These are a few words with a huge effect on whether a person moves forward or hesitates. These three places, errors, empty screens and buttons, give a lot of feedback to those who are learning, because the impact of improvement is easy to notice and measure.

The beginning of a skill that pays

Interface writing is one of those skills that seems small and has a big effect. A word exchanged in the right place can do more for the experience than weeks of development.

And the best part: it's an accessible skill. You don't need permission to start observing how people react to a product's words. You just need to change the question “is it pretty?” by the question “did it work?”, and have the humility to let the data answer.

If you're taking your first steps on this topic, start by measuring a single screen this week. There are other texts on the blog about product fundamentals and user experience that help you continue this journey more safely.