OpenAPI Specification (Swagger) in Rest API - Step-by-Step Execution

Concept Flow - OpenAPI Specification (Swagger)

Define API Info

↓

List Paths & Methods

↓

Describe Parameters

↓

Define Request & Response Schemas

↓

Add Security & Metadata

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Generate Documentation & Client Code

The OpenAPI Specification defines API details step-by-step, from info to paths, parameters, schemas, and security, ending with documentation generation.

Execution Sample

Rest API

openapi: 3.0.0
info:
  title: Simple API
  version: 1.0.0
paths:
  /hello:
    get:
      responses:
        '200':
          description: Success

This YAML snippet defines a simple API with one GET endpoint /hello returning a 200 success response.

Execution Table

Step	Section Processed	Action	Result
1	openapi	Read version '3.0.0'	Set spec version to 3.0.0
2	info	Read title and version	API named 'Simple API' version '1.0.0'
3	paths	Read path '/hello'	Register endpoint '/hello'
4	paths -> get	Read GET method	Define GET operation for '/hello'
5	responses	Read response code '200'	Set response description 'Success'
6	End	No more sections	Specification ready for use

💡 All sections processed, OpenAPI spec fully defined

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
spec_version	undefined	3.0.0	3.0.0	3.0.0	3.0.0	3.0.0	3.0.0
api_info	empty	empty	{title: 'Simple API', version: '1.0.0'}	{title: 'Simple API', version: '1.0.0'}	{title: 'Simple API', version: '1.0.0'}	{title: 'Simple API', version: '1.0.0'}	{title: 'Simple API', version: '1.0.0'}
paths	empty	empty	empty	{'/hello': {}}	{'/hello': {get: {}}}	{'/hello': {get: {responses: {'200': {description: 'Success'}}}}}	{'/hello': {get: {responses: {'200': {description: 'Success'}}}}}

Key Moments - 3 Insights

Why do we specify 'openapi: 3.0.0' at the start?

This tells tools which OpenAPI version to use. See execution_table step 1 where spec_version is set to '3.0.0'. Without it, tools might not understand the spec.

What happens if we forget to define responses for a path?

Responses describe what the API returns. In execution_table step 5, response '200' is set. Without responses, the API is incomplete and tools may warn or fail.

How does OpenAPI handle multiple HTTP methods on the same path?

Each method (get, post, etc.) is a separate key under a path. In step 4, 'get' is defined. You can add 'post', 'put', etc. similarly under the same path.

Visual Quiz - 3 Questions

Look at the execution_table, what is the API title after step 2?

A 'Simple API'

B 'My API'

C undefined

D 'API Version 1'

💡 Hint

Check the 'api_info' variable in variable_tracker after step 2

At which step is the GET method for '/hello' defined?

A Step 3

B Step 4

C Step 5

D Step 2

💡 Hint

See execution_table row where 'paths -> get' is processed

If we add a POST method to '/hello', which variable in variable_tracker changes?

A spec_version

B api_info

C paths

D responses

💡 Hint

Adding methods changes the 'paths' structure as shown in variable_tracker

Concept Snapshot

OpenAPI Specification (Swagger) defines REST APIs in a structured YAML/JSON format.
Start with 'openapi' version, add 'info' for API metadata.
Define 'paths' with HTTP methods and their parameters.
Specify 'responses' to describe outputs.
Use this spec to generate docs and client code.

Full Transcript

OpenAPI Specification (Swagger) is a way to describe REST APIs clearly. It starts by specifying the version with 'openapi: 3.0.0'. Then, the 'info' section gives the API a name and version. Next, 'paths' list the API endpoints like '/hello'. Under each path, HTTP methods like GET are defined. Each method includes 'responses' that explain what the API returns, such as a 200 success message. This structured format helps tools create documentation and client code automatically. The execution table shows how each part is read and stored step-by-step, and the variable tracker follows how the API details build up. Common confusions include why the version is needed, the importance of responses, and how multiple methods are handled on one path. Quizzes test understanding of these steps and variables. Overall, OpenAPI makes APIs easy to understand and use.