It is impossible to imagine modern development without APIs, or Application Programming Interfaces. Companies like Celadonsoft introduce APIs to enable data exchange among services, create product ecosystems, and scale businesses. However, developing an API Design requires not only functionality but also high performance, security, and usability.

In this article, we will discuss how to create an API that:

• Scale — keeps up with the growth of load and number of users without degradation of performance.
• Secure — protects data from leaks, attacks and unauthorized access.
• Flexible integration — easy to connect to different systems and services.
• Easy to use — has a well-designed structure and high-quality documentation.

We will cover the key stages of design, technology selection, security implementation and API optimization so that your business can effectively interact with partners, customers and internal services.

1. Defining the API’s Goals and Audience

Before the API design with .NET development has been started, it is important to understand what tasks it will solve and who it is intended for. Clearly defining the goals and audience will help create an effective and demanded solution that is easily integrated into the existing business ecosystem.

Business and User Needs Analysis

The API should be aligned with the company’s strategic goals and benefit end users. This requires:

• Define key usage scenarios — what tasks should the API solve? For example, scalable  business process automation, integration with external services or processing of large amounts of data.
• Identify user requirements — who is the main audience? Internal development teams, third party developers or end customers? Their needs and level of technical training will affect the API architecture.
• Analyze possible loads — what volumes of requests are expected? Will there be periods of high activity (for example, during e-commerce events)?

Market Research and Competitive Solutions

Before developing an API from scratch, it is worth exploring the existing solutions in the market:

• Competitor analysis — what API do competitors offer, how they solve problems, what errors do they make? This will help avoid common problems and find competitive advantages.
• Use of standards and best practices — REST, GraphQL, gRPC, SOAP — the choice of technology should be sound and fit business objectives.
• Growth and integration assessment — the API should not only be relevant at launch, but also ready to scale and integrate with new services.

2. Choice of Architectural Style and Protocols

Celadonsoft: “The development of an API starts with choosing a suitable architecture and protocol. This will determine how effectively the API can handle requests, scale and ensure data security.” Consider the main options and their application.

REST, SOAP, or GraphQL: Which Option to Decide?

The most common architectural styles of API include:

REST (Representational State Transfer)

• Based on standard HTTP methods (GET, POST, PUT, DELETE).
• Simple and easy to understand URL structure.
• Good scalability and caching.
• Best for most web applications and mobile APIs.

SOAP

• Uses XML for data exchange.
• More stringent specification and built-in security mechanisms.
• Suitable for banking, financial and corporate solutions requiring high reliability.

GraphQL

• Allows the client to request only the data needed, reducing the load.
• Flexibility in working with nested structures.
• Suitable for complex interfaces, mobile and one-page applications.

What Style Should You Decide for Your Business?

The choice depends on the specific tasks:

• If the API should be simple, scalable and easily integrated — REST.
• If strict security and reliability of data transmission is important — SOAP.
• If clients require flexibility in requests and get only the right data — GraphQL.

Communication Protocols: HTTP, WebSockets and gRPC

In addition to the architectural style, it is important to choose a data transfer protocol:

• HTTP/HTTPS is the standard for REST and GraphQL, suitable for most APIs.
• WebSockets — effective for working in real time (chat, exchange, streaming services).
• gRPC is a binary protocol optimized for high performance and microservices.

3. Designing API Structure

The well-designed API architecture is key to its convenience, security, and scalability. Errors at this stage can lead to integration problems, more complicated support and performance bottlenecks. To avoid these risks, it is important to follow the key principles of API design.

Defining Resources and End Points

Each API is a set of resources that clients call. Good definition of these resources and their interactions is the basis of a convenient API.

Identification of key entities. Determine what data and functionality to provide. For example, for the e-commerce API it can be: products, orders, users.

Logical route structuring. REST API should follow noun-based endpoints (use of nouns):

• GET /users/{id} — Receive user information
• POST /orders — create a new order
• GET /getUserById? id={id} — Failed because it violates the REST-style

Use of Meaningful and Consistent Naming Conventions

Uniformity in names is the key to a clear API that is easy to use.

URL structure. Use a uniform style (camelCase or snake_case) and avoid unnecessary verbs in your routes.

HTTP methods instead of extra parameters:

• POST /products — create product
• PUT /products/{id} – update product
• DELETE /products/{id} – remove product
• GET /deleteProduct? id={id} – HTTP methods duplication in URL

API Version Management

The API changes over time, and it is significant to ensure a smooth transition for users.

• Version is explicitly specified. Add the version to the URL (/v1/products) or request header (Accept: application/vnd.yourapi.v1+json).
• Support multiple versions. Ensure backward compatibility and warn customers about API obsolescence.

4. Providing API Security

Of course, not just data security but also security from attacks and leaks and illegal access is vital in regard to API Security. Reliable API protects business and users, ensuring product credibility.

Authentication and Authorization

You want to control who exactly and exactly what can do through the API.

• OAuth 2.0 and OpenID Connect are two standards for performing secure authentication and authorization.
• JSON Web Token is used to easily pass along encrypted information about a user in various requests. JWT is suitable for distributed systems where you need to quickly check access rights.

Protection Against Common Attacks

• Validation of input data. Always check the input data to prevent SQL Injection, XSS and other vulnerabilities.
• Request Limiting (Rate Limiting). Implement request limit mechanisms to avoid DDoS attacks.
• Cross-Origin Resource Sharing. That needs to restrict the access for some trusted domains just to prohibit requesting from anywhere.

Data Encryption and Secure Connections

• Use HTTPS. All APIs must work through HTTPS to encrypt the data being transmitted and protect it from interception.
• Encryption of sensitive data. For storing passwords, use secure hashing algorithms (e.g., bcrypt, Argon2).

API security is a continuous process. Regular audits, security audits and updates will help protect business and users from potential threats.

5. Optimizing API performance and scalability

The development of APIs is not only about designing logic and security, but also about providing high performance. To keep the API running fast and with high load, best practices for optimization must be applied.

Caching to Speed Up Requests

• Apply HTTP caching: ETag, Last-Modified to reduce server load.
• Using in-memory caching, Redis and Memcached stores frequently accessed data.
• Configure the CDN for static resources and API responses.

Load Limitation and Traffic Control

• Implement rate limiting (request per minute limitation) using the API Gateway.
• Use throttling (request slowing) to protect against overload.
• Set circuit breaker (automatic shutdown of overloaded services).

API Scalability

• Use microservice architecture to share load between services.
• Scale the API horizontally with load balancers.
• Optimize database queries (indexes, caching, data denormalization).

6. Documentation and API support

From the point of view of Celadonsoft, clear documentation is key to successful API integration. Developers should quickly understand how to work with your API, what parameters to pass and what responses to expect.

Automated Document Generation

• Use Swagger (OpenAPI) to automatically create interactive documentation.
• Generate documentation in Postman for easy testing.
• Update the documentation every time you change the API.

Detailed Examples of Use

• Provide code examples in popular languages (JavaScript, Python, Go).
• Describe the possible API errors and how to handle them.
• Develop sandbox (sandbox environment) for secure API testing.

Feedback and Support

• Create a forum or Slack channel for developers.
• Keep check-lists and FAQs with answers to popular questions.
• Provide SLA (Service Level Agreement) for B2B customers.