Spec-Driven Development in React Native: an MVP that lists the world's earthquakes, specified before writing code

TL;DR

A coding agent can already write a working app in an afternoon. The problem is no longer producing the code; it is something else: without a specification the agent doesn't write worse code, it writes excellent code for the wrong problem. Every question you didn't answer, it answers with a reasonable default, and you find out weeks later. Spec-Driven Development (SDD) attacks exactly that: write down first what the software must do, resolve in writing whatever is ambiguous, and treat the code as the output of that specification. I applied it to a React Native MVP built with Expo that does one thing-show a list of recent earthquakes anywhere in the world-because it is the kind of request that fits in one line and hides more decisions than it seems.

• SDD separates three artifacts: the specification (what and why), the technical plan (how) and the tasks. The agent implements against them instead of against a loose prompt.
• The real value is not the document: it is that ambiguities get flagged and resolved in writing before the agent chooses for you. Which earthquakes make the list, in what order, and what happens offline are product decisions, not code decisions.
• Acceptance criteria are written as a table of cases, and that same table becomes the test. If the row is not in the table, the behavior is undefined.

What Spec-Driven Development is and how it differs from prompting

A prompt is an instruction that gets consumed and disappears. A specification is a versioned file in the repository, reviewed in a pull request, that outlives the agent's session. That is the whole difference, and it is bigger than it looks. In the typical flow with an agent, you describe the feature in the chat and the result is a thousand lines of code plus a conversation nobody will reread. The important decisions-the minimum magnitude, how many hours back, what happens offline-were made in some intermediate turn of the chat. When someone asks why the app shows a magnitude 2.6 earthquake but not a 2.4, the answer is nowhere.

SDD splits the work into distinct artifacts, each at its own level of abstraction:

• Specification → what must happen and why
• Technical plan → how it gets built (stack, libraries, structure