OpenAPI Specification (Swagger) in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the OpenAPI Specification (Swagger)?

It is a standard way to describe REST APIs so that both humans and computers can understand the API's structure and behavior.

beginner

What file formats are commonly used for OpenAPI Specification?

OpenAPI files are usually written in JSON or YAML format.

intermediate

What is the purpose of the 'paths' section in an OpenAPI document?

The 'paths' section lists all the API endpoints and the HTTP methods (like GET, POST) available for each endpoint.

intermediate

What does the 'components' section in OpenAPI contain?

It holds reusable parts like schemas (data models), parameters, responses, and security schemes to avoid repetition.

beginner

How does OpenAPI help developers and machines?

It helps developers understand how to use the API and allows machines to generate code, tests, and documentation automatically.

Which section in OpenAPI defines the available API endpoints?

A info

B components

C servers

D paths

The 'paths' section lists all API endpoints and their supported HTTP methods.

What file formats can you use to write an OpenAPI Specification?

A JSON or YAML

B TXT or DOC

C HTML or Markdown

D XML or CSV

OpenAPI files are commonly written in JSON or YAML formats.

What is the main benefit of the 'components' section?

A To list API servers

B To store reusable definitions like schemas and parameters

C To describe API security only

D To provide contact information

'components' stores reusable parts to avoid repeating definitions.

Which HTTP methods are commonly described in OpenAPI paths?

A GET, POST, PUT, DELETE

B CONNECT, TRACE only

C FTP, SMTP

D SSH, Telnet

Common HTTP methods like GET, POST, PUT, DELETE are described in OpenAPI paths.

How does OpenAPI improve API documentation?

A By replacing the need for documentation

B By providing a manual to write code

C By automatically generating interactive docs and client code

D By encrypting API data

OpenAPI allows tools to generate interactive documentation and client code automatically.

Explain the main sections of an OpenAPI Specification document and their roles.

Think about where you describe the API info, endpoints, reusable parts, and security.

Describe how OpenAPI Specification helps both developers and machines work with APIs.

Consider benefits for understanding and automating API usage.

Practice

1. What is the main purpose of the OpenAPI Specification in REST APIs?

easy

A. To store user data securely

B. To execute API requests automatically

C. To replace the need for API servers

D. To describe the API endpoints, methods, and data formats in a standard way

Solution

1. Step 1: Understand OpenAPI's role

   OpenAPI Specification is designed to describe APIs clearly and consistently.

2. Step 2: Identify the correct purpose

   It documents endpoints, HTTP methods, parameters, and data formats for APIs.

3. Final Answer:

   To describe the API endpoints, methods, and data formats in a standard way -> Option D

4. Quick Check:

   OpenAPI = API description standard [OK]

Hint: OpenAPI is for describing APIs, not running or storing data [OK]

Common Mistakes:

• Confusing OpenAPI with API execution tools
• Thinking OpenAPI stores user data
• Believing OpenAPI replaces servers

2. Which of the following is the correct way to define an HTTP GET method for the path /users in OpenAPI YAML?

easy

A. paths:
get:
/users:
summary: Get all users

B. paths:
/users:
get:
summary: Get all users

C. get:
paths:
/users:
summary: Get all users

D. paths:
/users:
post:
summary: Get all users

Solution

1. Step 1: Check OpenAPI path structure

   Paths are keys under paths, then HTTP methods like get are nested under each path.

2. Step 2: Validate correct nesting and method

   paths: /users: get: summary: Get all users correctly places /users under paths and get under /users.

3. Final Answer:

   paths: /users: get: summary: Get all users -> Option B

4. Quick Check:

   Paths > /users > get [OK]

Hint: Remember: paths > endpoint > method > details [OK]

Common Mistakes:

• Swapping method and path levels
• Using wrong HTTP method for GET
• Incorrect YAML indentation

3. Given this OpenAPI snippet, what is the response code defined for a successful GET request to /items?

paths:
  /items:
    get:
      responses:
        '200':
          description: Successful response
        '404':
          description: Not found

medium

A. 200

B. 201

C. 500

D. 404

Solution

1. Step 1: Locate response codes under GET method

   The snippet shows responses under get for /items.

2. Step 2: Identify success response code

   Code 200 is labeled as "Successful response", indicating success.

3. Final Answer:

   200 -> Option A

4. Quick Check:

   Success = 200 HTTP code [OK]

Hint: Success responses usually use 200 code [OK]

Common Mistakes:

• Choosing 404 as success code
• Confusing 201 (created) with 200
• Ignoring response codes listed

4. Identify the error in this OpenAPI YAML snippet:

paths:
  /login:
    post:
      summary: User login
      responses:
        200:
          description: Login successful

medium

A. Summary field is not allowed under POST

B. Missing requestBody for POST method

C. Response code 200 should be a string '200', not a number

D. Path should start with a capital letter

Solution

1. Step 1: Check response code format

   OpenAPI requires response codes as strings, e.g., '200', not numbers.

2. Step 2: Verify other fields

   Summary is allowed; requestBody is optional; path case is flexible.

3. Final Answer:

   Response code 200 should be a string '200', not a number -> Option C

4. Quick Check:

   Response codes must be strings [OK]

Hint: Always quote response codes as strings in YAML [OK]

Common Mistakes:

• Using numeric response codes
• Assuming requestBody is mandatory
• Thinking summary is invalid

5. You want to document an API that returns a list of products with optional filtering by category. Which OpenAPI feature helps you define the optional category filter parameter for the GET /products endpoint?

hard

A. Use a query parameter with required: false under the GET method

B. Add a path parameter named category in the URL

C. Include category in the requestBody schema

D. Define category as a header parameter

Solution

1. Step 1: Understand parameter types

   Optional filters are usually query parameters, not path or header parameters.

2. Step 2: Define optional query parameter

   Set required: false for the category query parameter under GET.

3. Final Answer:

   Use a query parameter with required: false under the GET method -> Option A

4. Quick Check:

   Optional filters = query params with required false [OK]

Hint: Filters usually go as optional query parameters [OK]

Common Mistakes:

• Using path parameters for optional filters
• Putting filters in requestBody for GET
• Defining filters as headers