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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Use OpenAPI to describe the API a service publishes, and Spring Cloud Contract to turn important interactions into executable compatibility checks. OpenAPI describes the surface and shapes an API permits; a consumer contract tests the particular request-and-response behavior a consumer depends on. They solve different problems and can be used together.
OpenAPI describes the API; a contract tests an interaction
An OpenAPI document is a static description of an API: its operations, inputs, responses, and data shapes. It can describe the broader published interface, including behavior no particular consumer currently exercises. That makes it useful for documentation, design, and communicating the intended API surface.
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A consumer-driven contract instead captures an interaction that a consumer needs to keep working. In Spring Cloud Contract (SCC), a contract definition can drive provider verification and generate WireMock stubs for matching requests. The provider test checks that the service still honors the interaction; a consumer can use the stub to develop or test against that expected behavior without depending on a live provider.
Neither replaces the other. OpenAPI helps answer “What does this API offer?” A consumer contract helps answer “Does this provider still satisfy this consumer’s relied-upon behavior?” A well-described API can still change in a way that breaks an actual consumer, while a set of consumer contracts may cover only a small, intentional subset of the API.
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What an HTTP contract contains
SCC’s HTTP contract model requires both a request and a response. The request specifies the interaction the provider should recognize; the response specifies what the provider must return. Methods, URLs, headers, bodies, status codes, and matchers define the details.
Illustrative interaction
This compact example shows the information to capture for a consumer that fetches an order. It is a contract outline, not a complete, version-specific SCC DSL file.
request:
method: GET
url: /orders/42
headers:
Accept: application/json
response:
status: 200
headers:
Content-Type: application/json
body:
id: 42
status: PAID
createdAt: <runtime-generated timestamp>The method, path, and expected response body describe the consumer’s required case. The timestamp illustrates a value that may vary between calls. Use a matcher for values that are legitimately dynamic rather than asserting a fixed value that makes a test brittle. Keep stable requirements—such as the response status or a field’s required format—specific enough to catch a meaningful incompatibility.
In a real SCC project, the same interaction is expressed using a supported contract format, commonly Groovy or YAML, and the project’s configured plugin and dependency versions. The official Spring tutorial uses the spring-cloud-starter-contract-verifier dependency and demonstrates generated Java test classes for a REST contract. Because the exact DSL and build configuration depend on the project’s SCC version and build tool, treat the outline above as the contract’s content model, not copy-and-paste build configuration.
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- Define the interaction. Put the request and response requirements in an SCC contract. Include matchers where runtime-generated values vary, while keeping consumer-relevant expectations explicit.
- Run the provider build. The Spring Cloud Contract Verifier tooling uses the contract definitions to generate provider verification tests. Those tests exercise the provider and fail when its behavior does not match the contract.
- Generate and publish stubs. SCC can also generate WireMock stubs from the same definitions. A matching request can receive the contract’s declared response, letting a consumer test against the expected interaction.
- Run checks in CI. Verify provider behavior as part of the provider build and make the resulting contract or stubs available to consumers through the team’s chosen artifact or repository workflow. A shared broker is not intrinsic to writing or running SCC contracts.
The key design choice is what the contract asserts. If it is too broad, harmless implementation changes can break consumers’ tests. If it omits behavior a consumer actually depends on, a passing contract says little about that dependency. Treat each interaction as a compatibility promise with an identifiable consumer and a reason to exist.
Choose who owns the contracts and where they live
SCC supports both consumer-driven and producer-driven contract testing. In a consumer-driven workflow, consumers define the interactions they need and share them with the provider. In a producer-driven workflow, the provider owns the definitions and makes the resulting compatibility artifacts available to consumers. The choice affects how changes are proposed and who is responsible for keeping a contract representative; it does not change the basic request-and-response model.
Official SCC samples demonstrate contracts stored with producer applications as well as a separate-contracts-repository workflow. The samples also cover Maven and Gradle builds, REST, and messaging. A separate repository can make team-to-team contract changes visible independently of application releases. Keeping contracts with a producer can make ownership and implementation changes easier to coordinate in one project. Neither layout is mandatory; choose one that makes ownership, review, and CI publication clear.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.OpenAPI, Spring Cloud Contract, and Pact compared
Pact is a useful point of comparison because it is consumer-driven and interaction-focused. Pact describes itself as “a code-first consumer-driven contract testing tool, and is generally used by developers and testers who code.” Its pact files record the specification version in metadata. SCC supports consumer-driven contracts too, while also supporting producer-driven contracts in Spring applications.
| Question | OpenAPI | Spring Cloud Contract | Pact |
|---|---|---|---|
| Primary source of truth | A static API description and its published operations and shapes. | Contract definitions describing interactions to verify; can be consumer- or producer-driven. | Consumer-authored pact interactions; the specification version is recorded in each pact file’s metadata. |
| Typical ownership | API design or provider team, sometimes maintained collaboratively. | Consumer in a consumer-driven workflow, or provider in a producer-driven workflow. | Consumer-driven; consumers define the interactions they rely on. |
| Interaction granularity | Can describe the broader API surface and possible shapes. | Specific request-and-response interactions, with matchers for variable values. | Specific consumer interactions. |
| Generated or shared artifacts | The API description itself. | Provider verification tests and WireMock stubs can be generated from contracts. | Pact files that represent consumer-provider interactions. |
| Provider verification | A document alone describes the interface; it does not itself constitute SCC-style generated provider verification. | Generated tests verify provider behavior against matching contracts. | Consumer-driven contract workflow; exact verification setup depends on the Pact tooling in use. |
| Messaging | Describes HTTP APIs; it is not a substitute for a message-interaction contract. | Official samples include messaging examples as well as REST. | Not stated in the cited Pact overview. |
| Schema breadth | Well suited to describing the published API surface. | Focused on the interactions and expectations expressed in its contracts. | Focused on consumer interactions rather than documenting the entire API surface. |
| Repository layout | Often maintained alongside an API or provider, though the description can be shared separately. | Official samples show contracts with producers and in a separate contracts repository. | Pact files can be shared between consumer and provider teams; repository conventions vary. |
| Broker or registry | Not needed to author an OpenAPI document. | Not inherently required to define contracts, generate provider tests, or create stubs. | A broker is a possible way to centralize pact publication and verification; it is not the pact file format itself. |
The practical distinction is not “schema versus testing” as an either-or choice. Use OpenAPI when teams need a coherent description of the available API. Use SCC or Pact when teams need executable checks around the interactions consumers rely on. If a service has both a broad public interface and critical service-to-service dependencies, an API description plus narrowly scoped consumer contracts can make both responsibilities explicit.
Quick Recap
A practical adoption checklist
- Decide whether the API description and interaction contracts have separate jobs; avoid treating a generated API document as proof that a consumer’s behavior is verified.
- For each contract, identify the consumer or provider owner and the compatibility behavior it protects.
- Keep request and response expectations focused, and use matchers for genuinely variable runtime values.
- Choose whether contracts live with a producer or in a separate repository, then make ownership and CI publication part of that workflow.
- Use generated provider verification and stubs as complementary checks: one validates the real provider, while the other supplies the declared interaction to consumers.
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