# Spec-First vs Code-First Stubbing

**Short answer:** Code-first stubbing starts from the test and is immediately expressive; spec-first starts from the contract and is correct by construction. The first is a discipline of maintaining stubs; the second is a discipline of maintaining the spec. For a team that already versions an API, the spec is the durable source.

## What code-first optimizes for

Immediacy and control: write the stub in the test, match exactly, and run. The cost is that the stubs are a separate description that can drift.

## What spec-first optimizes for

| Property | Code-first | Spec-first |
| --- | --- | --- |
| Source | Stub code | Contract |
| Upfront cost | Low | Modeling |
| Drift | Common | Rare |
| Generated surfaces | None | Many |

## Why the spec scales

One contract drives the mock, the docs, and the tools, so a change is made once. Code-first stubs are updated in the tests and nowhere else.

## The honest tradeoff

Code-first is the pragmatic start for a JVM test. Spec-first pays back as the surface grows and the languages multiply.

This is part of the [Powerduck vs WireMock comparison](https://www.powerduck.com/blog/powerduck-vs-wiremock/). Next, read [the cloud comparison](https://www.powerduck.com/blog/wiremock-cloud-vs-powerduck-hub/).