AI Agent App Dev: Specs are Key, Not Just Typing

A solo developer is building a mobile app using an AI coding agent, finding that the process shifts the work upstream to detailed specification rather than just saving typing time. The app is in the identity and habit-change space. The developer started by creating the full database schema and all row-level security policies before building any screens. This approach was chosen because fixing a data model later is much more expensive than redoing user interface elements. Security policies were also implemented early to avoid complex migrations once user data exists. One near-miss involved almost building the onboarding flow before confirming the authentication system worked. The developer learned that vague instructions to an AI agent produce vague or incorrect code. For example, simply saying "update the user's streak" is not enough. The agent needs precise rules, such as how to increment or reset a streak based on specific conditions. This means developers must be highly specific in their instructions for AI agents to be effective.