Simple app ideas: 12 easy builds, each finished in an evening or two

What makes an app idea simple enough to finish?

Simple does not mean small in value. It means few moving parts. An idea is simple when you can list its screens on one hand, when it needs no account, and when you can calculate the right answer yourself for an example input. The last one matters most: it turns “does it work?” from an opinion into a check.

People who search for “easy app ideas” usually mean the same thing: something they can finish before the motivation runs out. Each idea here is meant to be finished in one to three evenings, and the estimates assume an AI coding tool and a clear prompt. They are estimates, not measurements.

How do you build a simple app, step by step?

1. Write the worked example first: real inputs and the exact output you expect.
2. Ask for one page with no login and no saved data. Add saving only after the example passes.
3. Run the example. Then try an empty field, a zero, a very large number and a typo.
4. Ask the tool for tests for the core calculation and read the test names, not the code.
5. Put it online as a static page, and send the link to one person who would use it.

Build a single-page web app. No backend, no login, no accounts.
User: [who and in what situation, one line].
Screen: [the fields to fill in, and one result area].
Rule: [the formula or logic in plain words].
Data: keep values in memory; add saving later only if I ask.
Do not build: charts, settings, export, sharing, anything not listed above.
Done when: [the worked example, with exact inputs and the exact expected result]. Empty or invalid fields show a short message, never NaN or Infinity.

To write prompts like this for your own idea, read how to write an app build prompt, and for a tool that assembles one, use the AI coding prompt builder.

Which simple app ideas are worth building first?

Each entry ends with a test case you can run on day one. If your result does not match, the app is wrong, not the example.

When does a simple app idea stop being simple?

Almost every idea above has a tempting second version that is not simple at all. Sharing the tip split with friends means accounts. Syncing the timesheet across devices means a database. Reading a pet’s vaccine records from the vet means a data agreement. None of that is wrong, but each is a new project and should start with its own worked example.

Ship the simple version and use it for a week before you decide which of these to add. If you find yourself wanting several, how to scope an MVP walks through choosing one.

Where can you find more simple app ideas?

The board at Post your build ideas is a free collection of app ideas people posted because they will not build them. Browse all ideas and look for ones whose first version fits on one screen. Every idea has a generated build prompt you can copy into Claude Code, Cursor or Lovable. If you have an idea you will never build, post it: no account, no email, and publishing is permanent.