Documenting REST APIs with OpenAPI and Swagger
Generate interactive, always-up-to-date documentation for your Spring REST APIs using the OpenAPI standard and Swagger UI.
Documenting REST APIs with OpenAPI and Swagger is a free Spring Boot 4 Complete Guide lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Boot 4 Complete Guide learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why Document Your API?
An API is only useful if consumers understand it. Good documentation describes endpoints, parameters, request bodies, and responses so other teams can integrate without guessing.
The OpenAPI Standard
OpenAPI is a vendor-neutral specification for describing REST APIs in a machine-readable format. Tools can read it to generate docs, client SDKs, and test suites.
Adding springdoc-openapi
The springdoc-openapi library scans your controllers and produces an OpenAPI document automatically. Just add the dependency and it works out of the box.
<dependency>
<groupId>org.springdoc</groupId>
<artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
</dependency>Exploring Swagger UI
Once added, visit /swagger-ui.html to get an interactive page where you can browse endpoints and try them live from the browser.
The Generated JSON Document
The raw OpenAPI document is served at /v3/api-docs. This JSON is what other tools consume to generate clients or import into platforms like Postman.
Describing Operations
Use @Operation to add a summary and description to an endpoint, making the generated docs clearer for consumers.
@Operation(summary = "Get a user by id")
@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) {
return service.find(id);
}Documenting Responses
The @ApiResponses annotation lets you list possible status codes and their meanings so callers know what to expect.
@ApiResponses({
@ApiResponse(responseCode = "200", description = "Found"),
@ApiResponse(responseCode = "404", description = "Not found")
})Documenting Models
Annotate DTO fields with @Schema to give examples and descriptions. This makes the model section of your docs self-explanatory.
public record UserDto(
@Schema(example = "Ada") String name
) {}Customizing API Metadata
Provide a title, version, and contact info with an OpenAPI bean so your documentation has a professional header.
@Bean
OpenAPI api() {
return new OpenAPI().info(new Info().title("User API").version("1.0"));
}Docs That Never Go Stale
Because the spec is generated from your actual code, the documentation stays in sync as your controllers change. This is the key advantage over hand-written docs.
Generating Client Code
Teams can feed the OpenAPI JSON into generators to produce typed clients in many languages, eliminating manual HTTP plumbing on the consumer side.
Quick Check
Test your understanding of API documentation.
Recap
You added springdoc-openapi, explored Swagger UI, and enriched docs with @Operation, @ApiResponses, and @Schema. Your API is now self-documenting and consumer-friendly.
Frequently asked questions
Is the “Documenting REST APIs with OpenAPI and Swagger” lesson free?
Yes — the full text of “Documenting REST APIs with OpenAPI and Swagger” is free to read here on the web, and the Spring Boot 4 Complete Guide course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Boot 4 Complete Guide course, upgrade to CoddyKit PRO.
What will I learn in “Documenting REST APIs with OpenAPI and Swagger”?
Generate interactive, always-up-to-date documentation for your Spring REST APIs using the OpenAPI standard and Swagger UI. You practise Spring Boot 4 Complete Guide with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Spring Boot 4 Complete Guide?
No prior experience is required. Spring Boot 4 Complete Guide on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Documenting REST APIs with OpenAPI and Swagger” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Spring Boot 4 Complete Guide lesson?
Yes. Every Spring Boot 4 Complete Guide lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Creating REST Controllers
- Handling HTTP Requests & Responses
- Input Validation & Error Handling
- Documenting REST APIs with OpenAPI and Swagger