Building Mini Apps: Keep the Problem Small and the Learning Useful
Start with a task you can describe plainly
A mini app gives a product idea a practical test: can someone open it, understand it and finish something useful?
The temptation is to add features until the tool feels substantial. A dashboard, an account, a few charts and a settings page can make a small project look like a complete product. They can also make the original task harder to find.
I think a better starting point is one sentence: this tool helps a particular person complete a particular task. If that sentence needs several unrelated verbs, the first version is probably too broad.
Define the smallest complete experience
Small does not mean unfinished. A calculator can have a narrow purpose and still need understandable controls, keyboard support, sensible error behavior and a usable mobile layout.
A planning tool has a different challenge. Its output depends on assumptions. The interface needs to make those assumptions clear enough that the user can interpret the result.
The smallest complete experience includes the parts that help someone succeed and recover when something goes wrong. It does not have to include everything that might eventually be useful.
Before building, write down three things: what the user enters, what they get back, and how they know the result is relevant to their task. This exposes gaps that a feature list can hide.
Treat assumptions as part of the interface
A number displayed confidently can look more certain than it is. If a result depends on a rate, a date convention or a contribution schedule, those inputs belong close to the result.
For a scenario tool, the user should be able to distinguish their inputs from defaults. If the result changes, they should be able to understand what drove the change. This is a product-design issue as much as a calculation issue.
Explain limitations in plain language. A useful explanation tells the user what the tool includes and what it leaves out. It should help them interpret the output without requiring them to read implementation details.
Keep the first release easy to explain
Before adding another feature, ask whether it helps complete the original task or introduces a new one.
Export might be essential if the task ends with sharing a result. It might be unnecessary if someone only needs a quick calculation. Sign-in might be justified for data that needs to follow a user across devices. It creates needless friction if the tool works well without an account.
The answer comes from the task. There is no universal checklist that every mini app needs to satisfy.
Publish the story alongside the tool
An app page should do more than provide a launch button. It can explain who the tool is for, show an example, describe the supported use cases and document what changed.
That story is especially useful in a personal portfolio. A visitor can try the output and understand some of the decisions behind it. Which problem was chosen? What was kept out of scope? Which assumptions needed to be visible? What would be improved next?
A short, dated release note is enough for an update. “Added an export that includes the selected assumptions” explains a change better than “major improvements.” Use actual changes and dates, and avoid making an old app look newly released just because its page was edited.
Learn from the points of friction
Useful feedback often begins with a simple observation: someone could not find a control, misunderstood an input or did not know what to do with the result.
Ask what the person was trying to do and where they became uncertain. Fixing that gap may create more value than adding another capability.
The advantage of a mini app is that the connection between a decision and its effect is easier to see. Keep the scope small enough to preserve that connection, and complete enough that the tool earns another visit.