API

What Is an API?

API stands for Application Programming Interface. It defines rules and formats that allow different software systems to communicate with each other.

Types of APIs

Open APIs

Also called public APIs. These APIs are publicly available and can be accessed with minimal restrictions.

Partner APIs

These APIs are shared with specific business partners and usually require authorization, contracts, or licensing.

Internal APIs

Also called private APIs. Organizations build these for internal systems and teams to improve reuse, integration, and productivity.

Composite APIs

Composite APIs combine multiple service or data calls into a single request to reduce round trips and improve performance.

Web Service API Styles

SOAP

Uses XML-based messaging with strict standards and contracts (commonly WSDL).

REST

Uses HTTP methods such as GET, POST, PUT, PATCH, and DELETE to work with resources.

JSON-RPC

A lightweight remote procedure call protocol that uses JSON for request and response payloads.

XML-RPC

A remote procedure call protocol that uses XML for payload formatting and is typically transported over HTTP.

API Testing Tools

Postman

Postman is one of the most widely used tools for manual and automated API testing. It supports request collections, environments, scripting, and API documentation.

Ping API

Ping API is an API testing platform that supports request validation and automated test scripts.

vREST

vREST is an online API testing and mocking tool for REST/HTTP APIs. It can be used for automated testing, recording, and specification workflows.

Key Features of APIs

  • Provide access to valuable data, services, or business functionality.

  • Support product and platform business models.

  • Are flexible and can be adopted quickly by developers.

  • Can be managed and measured with monitoring and analytics.

  • Offer strong developer support through docs, SDKs, and tooling.

API Design Best Practices

Resource-Based Endpoints

Prefer resources over action-oriented naming.

Bad:

1GET /getUsers
2POST /createUser
3GET /getUser/{id}
4PUT /updateUser/{id}
5DELETE /deleteUser/{id}

Good:

1GET /users
2POST /users
3GET /users/{id}
4PUT /users/{id}
5DELETE /users/{id}

Use Proper HTTP Methods

Method

Purpose

GET

Retrieve data

POST

Create a new resource

PUT

Replace or update an existing resource

PATCH

Partially update an existing resource

DELETE

Remove a resource

Use Correct Status Codes

Do not always return 200. Choose a status code that matches the outcome.

Status Code

Meaning

200 OK

Request was successful

201 Created

Resource was created successfully

204 No Content

Request was successful, no response body

400 Bad Request

Request is invalid or cannot be processed

401 Unauthorized

Authentication is required

403 Forbidden

Authenticated, but not allowed

404 Not Found

Requested resource does not exist

500 Internal Server Error

Unexpected server-side failure

Consistent Naming and URL Structure

Use predictable naming for endpoints, parameters, and payloads.

Good:

1/users
2/users/{id}
3/users/{id}/posts
4/users/{id}/comments

Bad:

1/getUserData
2/createNewUser
3/updateUserInfo
4/deleteUserAccount
5/fetchCommentsForPost

URL hierarchy should reflect resource relationships.

Versioning Strategy

Version APIs from the beginning.

Common example:

1/api/v1/products
2/api/v2/products

Pagination

Avoid returning very large result sets in one response.

Offset-based pagination:

1GET /products?page=1&limit=20

Cursor-based pagination (preferred for large datasets):

1GET /products?cursor=abc123&limit=20

Standard Response Format

Keep response structure consistent across success and error cases.

Success example:

1{
2    "status": "success",
3    "data": {
4        "id": 1,
5        "name": "Product Name",
6        "price": 19.99
7    },
8    "message": null
9}

Error example:

1{
2    "status": "error",
3    "data": null,
4    "message": "Product not found"
5}

Authentication and Security

Minimum baseline:

  • Use HTTPS to protect data in transit.

  • Use JWT for stateless authentication where appropriate.

  • Use OAuth 2.0 for third-party integrations.

  • Apply rate limiting to prevent abuse.

  • Validate and sanitize input to reduce injection and parsing risks.