API Development - An Ultimate Guide to developing robust API's

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API Development – Ultimate Guide to developing robust API’s

Published datePublished: Jun 5, 2020 Last Updated Last Updated: Mar 16, 2023 ViewsViews: 8952reading time10 min. read
Deepak Sinha

Deepak Sinha

Deepak is a hands-on Technology Leader with expertise in designing software solutions for various successful projects for multinationals. He has total experience of 15+ years and has worked on all the phases of application development and has good experience in open source and mobile technologies. He is passionate on new Technologies and has strong interest on Machine Learning, Artificial Intelligence etc.
API Development – Ultimate Guide to developing robust API’s

Application Programming Interface (API) is a basic building block of procedures and functions that enable the mobile app development that access data and features of other applications, services. In other words, it connects different applications and let them complement each other.

APIs are like a boon for developers as well as enterprises. When writing a new program, a developer does not have to begin from scratch to build a core application. Instead, they can utilize (contract) certain functionalities by using an existing piece to do a better job. This article will explore various types of APIs such as private and public APIs, REST APIs and SOAP APIs.

Categories of API

APIs can be divided into four categories:

Categories of API

Open API or Public API – This type of APIs are publicly available for developers and provide them with programmatic access to a proprietary software application or web service.

Partner API – Unlike Public APIs, they are not freely accessible for everyone. A company or developer needs a specific entitlement to access these APIs. There is an on-boarding process with a specific authentication workflow to gain access to partner APIs.

Internal API or Private API – They are not exposed to external users and are meant to be used across different internal development teams for enhanced productivity and utilization of services.

Composite API – Such APIs combine different service and data APIs through API development. They are built by combining the existing API functions that can perform multiple tasks in a single call. It makes the execution process faster and enhances the performance of the listeners in the web interfaces.

What are REST APIs and SOAP APIs?

REST APIs use HTTP requests to interact with web resources and standard HTTP methods like GET, POST, PUT, and DELETE to perform CRUD operations. A unique URL identifies each resource, and the server responds with a representation of the resource in a standard format like JSON or XML. REST APIs are stateless, making them highly scalable and easy to use across platforms. They have become popular for developers to build web services and create integrations between different systems due to their simplicity, flexibility, and scalability.

SOAP (Simple Object Access Protocol) APIs are a type of web-based API that use XML to exchange structured messages between applications over a network. SOAP APIs rely on a set of strict rules and protocols to ensure the messages are sent and received correctly.

Generally, in the case of API categories for web services, developers prefer RESTful architecture or REST APIs. Enterprise apps that need high-level security and are backed by more resources are inclined towards SOAP-based APIs.





Stands For

Representational State Transfer

Simple Object Access Protocol



Function Driven

Data Format

Uses HTML, XML, JSON and more

Uses XML only


Is lightweight and needs lesser resources

Needs more bandwidth and resources



WS- Security & SSL

Data Cache

Can be Cached

Cannot be Cached

Payload Handling

Needs no knowledge of the API

Has a strict communication contract and needs to every detail before communication

Atomicity, Consistency, Isolation, Durability

No ACID Compliance

Built-in ACID Compliance

Generally, in case of APIs for web services, developers prefer RESTful architecture and for enterprise app that needs high-level security and is backed by more resources, they incline towards SOAP API.

Basic API Terminology That You Must Know

Following are some of the common terminologies involved in API development.

API Key – An API key is a unique identifier or code passed in by computer programs to authenticate the developer or user or calling program.

Endpoint – Touchpoints of the interaction between API and a server are known as the Endpoint.

JSON – JavaScript Object Notion (JSON) is a data format used for APIs to interchange data on the web. The interchange of data can happen between two applications or a server and a web application.

GET – GET is a method which is used to request data from a server at the specified resource.

POST – POST is a method which is used to send data to the API server to create or update a resource.

OAuth – OAuth is an authorization framework or open-standard authorization for APIs. It provides secure and limited access to end user’s data to be used by third-party websites or applications without accessing their password.

Latency – The time taken by an API for processing a request and responding is known as Latency.

Rate-Limiting – It is a process of controlling the rate of incoming and outgoing traffic. It is also defined as the number of requests a user hits to API each time.

API Throttling – It refers to the process of controlling the usage of APIs by the consumers for a specific duration.

Tools for API Development

Apigee It is Google’s API development management tool. It is helpful when a developer is creating connected apps, or a company is updating legacy apps or facilitating data transfer between services and apps.

Dredd It is an HTTP API testing framework. It takes an API description document, creates expectations based on requests and responses documented in the document, makes requests to tested API, checks whether API responses match the documented responses, validates the results.

API Spec Converter – It is a tool used by developers to convert between different API spec formats.

APIMatic It is a developer experience platform for web APIs. It is used by developers for generating SDKs for their APIs for 10 platforms and keeping them in sync with the API updates.

Using this tool also allows developers in converting API descriptions into multiple formats including Swagger, OAI format, WADL, RAML, API Blueprint, IO Docs, Postman Collections, and HAR 1.4 and more.

Sandbox It provides an easy and quick mock RESTful API from API definitions. It reduces the cost and risk associated with calling third party API during testing.

Postman It’s an interactive and automatic that allows developers to run, test, document, and evaluate the performance of their API.

SoapUI It is an open-source testing tool. It can operate on cross-platforms and can automate both functional tests as well as non-functional tests. It is generally used for executing compliance, regression, security, and load tests for Web APIs.

Swagger It is an open-source framework that is used for developing APIs. Swagger is being used by top technology giants such as Apigee, GettyImages, Microsoft, and PayPal.

JMeter It is also open-source software. It is used for performance testing of a RESTful API.

Must-have features in API design

Here’ a list of some important points which a developer should keep in mind before and during the creation of an API. It will accelerate the development process and help everyone on the team to stay on the same page.

Authentication and Authorization

Authentication means verifying the right identity. Deciding whether a verified user is or is not allowed to perform an action on a specific source is an authorization. For example, Sam (an authenticated user) can get a resource but not allowed to create a resource.

JWT, OAuth, and OAuth2 are some of the commonly used specifications used to handle this authentication and authorization.

Query, Filter, Sorting & Pagination

With time your database will grow. Once that happens, you will begin to notice that some resources are taking longer than usual time to retrieve. Some of the common ways to approach this scenario are to cache your objects and/or create pagination/filtering.

By sorting, we ensure that data is received by the user one by one as per the requirement, modification, and the condition applied. Paging is the process of determining how much data must be displayed and at what frequency. These things ensure minimum processing time, good response time, and high-level security.


Developing a Cache strategy helps the user in retrieving resources at an amazing speed. Once your data is ready to be consumed in an in-memory database the cost of your requests will get reduced. You may use tools like Memcached and Redis for this purpose.


API wrappers are language-specific packages or containers that combine sets of API calls into user-friendly functions. The wrapper calls multiple API calls without the interaction of the user.


HATEOAS (Hypermedia as the Engine of Application State) is a module of the REST application architecture which is distinctive from most other network application architectures. Any content that contains a link to other forms of media like images, text, and videos is known as hypermedia.

With HATEOAS, a client can interact with a REST API entirely through the responses provided dynamically by the server. This concept is like a 

web-user browsing through web pages by clicking on hyperlinks to reach a destination.

Error handling

Good error handling can make debugging easier by identifying whether the problem is a result of a client or server error. For some errors, the client can simply change the request, while for others they need to contact support. Some basic and helpful methods of error handling include:

  • Using well-known standard error codes
  • Providing the right number of errors
  • Explaining the cause of the error
  • Separating general and domain errors


Verifying the correctness of data is known as validation in APIs. There are two types of validation, client-side and server validation. Client-side validation is generally done by giving prompt feedback, for example highlighting the wrong entry in red or tooltip for correction, etc.

Server-side validation is a crucial component of API development. It includes some mundane tasks like validating whether a property is required or what kind of property it is (email, account number, etc) or if a property is not required in case another property is already there.


API testing is like software and QA testing. It includes testing APIs directly and as a part of integration testing to determine if they meet expectations for functionality, reliability, performance, and security. Postman, SoapUI, and JMeter are some of the popular tools used for API testing.

Best Practices for Designing a great API

Documentation is essential

API documentation is a technical document that contains detailed information about the ways to effectively utilize and integrate with it. Generally, it covers details about the functions, classes, returns types, arguments, etc.

Consistency & Stability

You should aim at creating intuitively consistent API. Reuse the same naming conventions throughout. Developers should be able to guess parts of your API even without reading the documentation. Maintenance of old versions of APIs is also important.


Anticipating all possible ways in which users will want to use your API is not possible. Every client platform is also not consistent. Considering these future unknown scenarios, its good to have some degree of tolerance with your input and output constraints.


As an API provider, you need to keep it secure but not difficult to use. If a user must write code or spend more than five minutes for authentication, it is not even close to being user-friendly. Token-based authentication is one of the preferred ways of authentication.

Ease of Adoption

Finally, keep it simple and make sure people can use your API and it works the first time and every time.

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