🍃✍️Swagger OpenAPI Spring: Document Your Spring REST APIs with Annotations

Author: Vincent Vauban

Original post on Foojay: Read More

Table of Contents

Swagger OpenAPI Spring is a simple way to turn your Spring REST APIs into clear and reliable documentation.
By adding a few annotations to your controllers and DTOs, you keep your API contract close to the code, which makes it easier to read, test, and evolve over time.

🔵 TL;DR

🧾 Briefly

🔹Use Swagger/OpenAPI annotations to turn your Spring REST APIs into clear, living documentation.
🔹You do not need extra UI tools, and your code and docs stay in sync. 🔄
🔹Start with @Tag, @Operation, @Parameter, @ApiResponse, and @Schema.
🔹This gives you clean docs, “try it out” support, and reliable API contracts. 🚀

🔵 WHY IT MATTERS

💡 Swagger OpenAPI Spring clarifies APIs, accelerates onboarding, improves integrations, and simplifies stable versioning.

Furthermore, Swagger OpenAPI Spring does more than generate a nice page.
It removes confusion and speeds up work for your team.

  • ✅ Faster onboarding, so new developers ask fewer “what does this endpoint do?” questions.
  • 📌 Accurate, up-to-date API docs that ship with the code itself.
  • 🤝 Better client integrations, for example with code generation, tests, and SDKs.
  • 📏 Clear contracts that make versioning and backward compatibility easier to manage.

In short, you describe the API once and reuse it everywhere.
This works both inside your company and for external clients.

🔵 CHEAT SHEET (MOST-USED ANNOTATIONS)

📚 Swagger annotations keep controllers readable and docs in sync with code as it evolves.

Moreover, these are the annotations you will use most of the time.
They keep your controllers readable and your API docs useful.

  • @Tag — Groups endpoints by feature or domain. It also creates a clear section in the UI.
  • @Operation — Describes one endpoint: summary, description, operationId, and tags.
  • @Parameter — Documents path, query, or header parameters: name, example, and required flag.
  • @ApiResponse — Describes results such as HTTP codes, messages, and the content schema.
  • @Schema — Documents your models: field types, examples, limits, and enums.

Because these annotations live in your code, your docs change when the code changes.
You no longer need to search through outdated wiki pages or slide decks.

🔵 MINI EXAMPLE (SPRING)

🧪 Example OrderController shows self-documented endpoints with Swagger annotations, making API behavior immediately clear.

Secondly, the following example shows how a simple OrderController can become self-documented with Swagger OpenAPI Spring annotations.

@Tag(name = "Orders", description = "Create and read customer orders")
@RestController
@RequestMapping("/api/orders")
class OrderController {

  @Operation(
    summary = "Get order by id",
    description = "Returns a single order with line items."
  )
  @ApiResponse(
    responseCode = "200",
    description = "Order found",
    content = @Content(schema = @Schema(implementation = OrderDto.class))
  )
  @ApiResponse(responseCode = "404", description = "Order not found")
  @GetMapping("/{id}")
  public OrderDto getOrder(
    @Parameter(description = "Order ID", example = "42")
    @PathVariable Long id
  ) {
    // ...
    return null;
  }
}

class OrderDto {
  @Schema(example = "42")
  Long id;

  @Schema(
    description = "ISO-8601 creation date",
    example = "2025-11-08T09:30:00Z"
  )
  String createdAt;

  @Schema(
    description = "Total amount in EUR",
    example = "129.90",
    minimum = "0"
  )
  BigDecimal total;
}

In this small class, the contract is visible at a glance. 👀
Developers can read the code and understand the API behavior right away. ✅

🔵 HOW TO START TODAY

🏁 Start small with key Swagger annotations, then gradually extend docs and schemas as your API grows.

So, you do not need to add every annotation on day one.
Instead, grow the documentation step by step.

  • Pick one controller and add a @Tag on the class.
  • Add a short @Operation on each public handler method.
  • Describe the most important parameters with @Parameter.
  • Add @ApiResponse for the main success and error cases.

Over time, you can extend this with @Schema on your DTOs.
This way, your models become just as clear as your endpoints. 🌐

🔵 TAKEAWAYS

📌 Swagger OpenAPI Spring keeps docs near code, improving discoverability, safety of changes, and developer experience.

Lastly, to sum up, Swagger OpenAPI Spring annotations give you a simple way to keep docs close to the code.

  • ✅ Start small: add @Tag and @Operation to your controllers today.
  • 🗣️ Be generous with example and description. They help reduce support questions.
  • 🚦 Use @ApiResponse for every expected HTTP code (200/201/400/404/422/500).
  • 🧩 Keep DTOs annotated with @Schema, so fields are documented where they live.
  • 🔍 Treat docs as code. Review them in pull requests and update them as your versions change.

When you follow these habits, your API is easier to discover.
It also becomes safer to change and more pleasant to use. 😌

🔵 GO FURTHER WITH JAVA CERTIFICATION

🎓 Java and Spring certifications deepen your knowledge and help you design stronger, more reliable APIs.

Subsequently, if you want to go deeper into Java and Spring, you can also train for certification. 📚
This can help you build stronger APIs and understand the platform in more depth. 💪

Java 👇

https://www.udemy.com/course/ocp-oracle-certified-professional-java-developer-prep/?referralCode=54114F9AD41F127CB99A

Spring 👇

https://www.udemy.com/course/spring-professional-certification-6-full-tests-2v0-7222-a/?referralCode=04B6ED315B27753236AC

SpringBook 👇

https://leanpub.com/springcertification

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