# WireMock Java Stubs vs an OpenAPI Mock Server

**Short answer:** Java stubs are expressive and live in the test code; a spec mock is generated from the contract and serves every language. The first is a code-level description of the API; the second is a rendering of the source. The boundary is the JVM.

## What Java stubs guarantee

Maximum control over matching, transformations, and state in the same language as the tests. They are a separate, maintained description of the API.

## What a spec mock guarantees

| Property | Java stubs | Spec mock |
| --- | --- | --- |
| Source | Test code | Contract |
| Language | JVM | Any |
| On change | Update code | On save |
| Drift | Common | Rare |

## Why the language boundary matters

A JVM mock serves the JVM tests. A spec mock serves every client, so a polyglot team shares one target.

## The decision rule

Java stubs are right for a JVM codebase that wants control. A spec mock is right for a multi-language team that wants the contract to own the mock.

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