What is an API? How Does an API Work?

May 04, 2024

In modern technology, the role of APIs has become extremely important and widespread. They play a key role in connecting various applications, from mobile apps, websites, to Internet of Things (IoT) systems, and cloud services. APIs enable companies and developers to leverage and reuse functionalities available from external sources, helping to accelerate product development, enhance user experience, and expand their application scope flexibly. With the rise of the digital industry and the development of digital platforms, APIs have become the centerpiece of connectivity and integration between systems and services, playing an indispensable role in building applications and providing solutions for the increasingly diverse needs of users.

1. Introduction to APIs

API stands for “Application Programming Interface,” which is a set of rules, protocols, and tools that allow different software applications to interact and communicate with each other. It is a way for various software programs to exchange data and functionality without needing to know specific details about how each other works. The significance of APIs lies in creating a standardized communication gateway for different applications, enabling them to easily and efficiently exchange information, requests, and responses.

APIs make the connection between applications more flexible. Instead of needing to understand the inner workings of each application, we can use APIs to access functions, data, or services from another application without needing to know the technical details internally. Specifically, APIs enable applications to:

  • Accessing data: APIs enable applications to securely and efficiently access and retrieve data from external sources.
  • Utilizing functionality or services: APIs provide a means to utilize functions or services from other applications, expanding the capabilities of the current application without the need to develop them from scratch.
  • Sending requests and receiving responses: Applications can send requests through an API and receive responses containing the requested data or results.

For example, when you use a mobile app to view weather information, the app may use an API from a weather service to access the latest weather data and display it on your app’s interface. APIs are also used for user authentication, integrating online payments, accessing databases, and many other functions. APIs can be provided in various forms, including RESTful APIs, SOAP APIs, GraphQL, and many other standards, each with its own advantages and suitability for specific use cases.

2. How APIs Work 

2.1. Communication Process between Client and Server

API operates through a communication process between the client (user or application) and the server (where data or necessary functions are stored). This process occurs through predefined methods and protocols for transmitting information and requests between the two parties.


  • The client initiates a request using methods such as GET (retrieve data), POST (add new data), PUT (update data), DELETE (delete data), PATCH (partially update data), OPTIONS (request options), and sends it to the server via a specific URL (referred to as an endpoint) of the API. Processing the Request

Processing the Request

  • Receiving the request: The server receives the request from the client through the designated endpoint.
  • Handling the request: The server executes actions corresponding to the received request. This may involve accessing or updating data from the database, executing specific logic or functions provided by the API, and processing data according to the client’s request.


  • Generating the response: After processing the request, the server generates a response containing the requested information or results.
  • Sending the response to the client: The server sends this response back to the client through the same communication channel, typically in the form of an encoded data packet.

This operational mechanism often relies on specific principles and protocols such as RESTful (Representational State Transfer), SOAP (Simple Object Access Protocol), GraphQL, and various other protocol standards.

2.2. API Operation Methods

The operation of an API relies on specific HTTP methods to send requests and receive responses from the server. These methods define the specific actions that the client wants to perform regarding the data or services provided by the server.

Access Methods to API via HTTP:

  • GET: Used to request data from the server. It’s typically applied when the client wants to retrieve information from the server, such as fetching data from a specific data source.
  • POST: Employed to send new data to the server. It’s commonly used when the client intends to create new data on the server, such as creating a new post on a social network or adding a record to a database.
  • PUT: Utilized to update existing data on the server. The client sends new data to completely replace the old data at a specific URL on the server.
  • DELETE: Used to remove data from the server. When the client sends a DELETE request to an endpoint, the server will delete the data corresponding to that URL.
  • PATCH: Employed to update a small part of the data on the server. Unlike PUT, PATCH allows the client to send an index and the data to be updated without replacing the entire dataset.

After the server receives and processes the request, the response returned to the client typically includes an HTTP status code. This status code informs about the outcome of the request, such as “200 OK” for a successful request, “404 Not Found” if the data does not exist, or “500 Internal Server Error” if there is an error on the server side. The response also includes data or messages that the client needs to continue its next operation.

3. Popular Third-Party Services

Electronic Payments

  • Online Payment Gateways: PayPal, Stripe, Square
  • Digital Wallet Services: Apple Pay, Google Pay, Samsung Pay
  • QR Code Payment Systems: Alipay, WeChat Pay

Social Media Integration

  • Content Sharing Platforms: Facebook, Twitter, LinkedIn
  • Embeddable Media and Content Sharing: Instagram, Pinterest, YouTube
  • Login and Information Sharing Tools: OAuth, Google Sign-In, Facebook Login

Email Marketing

  • Bulk Email Sending Platforms: Mailchimp, SendGrid, Constant Contact
  • Email Marketing Automation Services: HubSpot, ActiveCampaign, ConvertKit
  • Email List Management and Performance Analysis Tools: AWeber, GetResponse, Campaign Monitor

Content Management Services (CMS)

  • WordPress: Popular content management system
  • Drupal: Flexible and extensible CMS platform
  • Joomla: Versatile content management system

Analytics and Tracking Tools

  • Google Analytics: Website performance analysis and measurement service
  • Hotjar: Website user behavior tracking and analysis
  • Mixpanel: Data analysis and user interaction tool

Chat and Online Support

  • LiveChat: Online chat service for customer support
  • Zendesk Chat (formerly Zopim): Integrated chat tool and support management
  • Intercom: Online customer chat and support management platform

Geolocation and Maps Services

  • Google Maps API: Map and geolocation service from Google
  • Mapbox: Customizable map platform with flexible integration capabilities
  • OpenStreetMap: Open-source community map service

Mobile App Services

  • Firebase: Google’s mobile app development platform
  • OneSignal: Push notification service for mobile apps and browsers
  • Appsflyer: Mobile app analytics and tracking tool

E-commerce and Online Commerce Services

  • Shopify: Online store building platform
  • WooCommerce: E-commerce plugin for WordPress
  • Magento: Open-source and powerful e-commerce platform

SEO and Optimization Services

  • SEMrush: SEO and keyword research platform
  • Yoast: SEO optimization plugin for WordPress
  • Ahrefs: Backlink analysis and keyword research tool

Chatbot and Artificial Intelligence Services

  • Dialogflow: Google’s chatbot building platform
  • ManyChat: Chatbot service for social media platforms
  • Watson Assistant: IBM’s virtual assistant service

These services offer diverse solutions ranging from feedback collection, SEO optimization, chatbots, scheduling, hosting to market research, expanding interaction capabilities, and optimizing user experience on websites.

4. Benefits of Using APIs

Utilizing APIs brings numerous important advantages not only in terms of flexibility and interaction but also in scalability and ease of integration and source code reuse.

4.1. Flexibility and Scalability

APIs enable seamless connectivity and interaction between different applications or services. Instead of building every functionality from scratch, applications can leverage functions or data from external sources through APIs. This creates favorable conditions for expanding the functionality or features of an application without the need to alter or intervene in the core source code.

Imagine a mobile application like a weather app, which uses APIs from various data sources to provide diverse and accurate weather information. This app doesn’t need to integrate or collect weather data from scratch. Instead, it can use APIs from weather service providers such as OpenWeatherMap or WeatherAPI. By using these APIs, the app can query weather information from professional data sources without building its own weather data collection system.

When a user opens the app and requests weather information, the app sends a request through the integrated API to the weather service provider. This API returns the necessary weather data, such as temperature, humidity, forecasts, and other information, which the app then displays to the user. Through the API, the app can easily expand its features or update weather information without having to make significant changes to the core source code. With available APIs from different weather service providers, the app can flexibly switch between data sources easily, without significantly impacting the user experience.

4.2. Enhanced Interaction and Availability

Consider an e-commerce application utilizing APIs from various payment gateways to offer diverse payment methods to users. When users decide to purchase a product within the app, they can choose from various payment methods such as credit cards, e-wallets, or bank transfers. The app doesn’t need to build the entire payment system from scratch. Instead, it can integrate APIs from different payment providers such as PayPal, Stripe, or banks to provide a rich array of payment options for users.

When users select a payment method and complete the transaction, the app sends a payment request through the API of the respective payment service provider. The API processes the transaction and returns the result, notifying the app whether the transaction was successful or not. Thanks to APIs, the app can offer users a flexible and convenient shopping experience with multiple payment options, without having to build and maintain a complex payment system from scratch. This enhances user interaction with the app, giving them the ability to choose and complete payments quickly and easily.

4.3. Ease of Integration and Code Reusability

APIs provide a standardized approach to accessing functionality or data from external sources. This helps developers integrate functionality or data from various sources flexibly and efficiently, without the need to build everything from scratch. Reusing code through APIs also accelerates development speed and minimizes errors resulting from rewriting code.

Imagine you’re building an e-commerce application and you want to integrate user authentication functionality through an API from an authentication service provider. Instead of building an authentication system from scratch, you can use APIs from authentication service providers such as Auth0 or Firebase Authentication. You integrate this API into your application, allowing users to register, log in, and manage their personal information easily.

When users want to log in to the application, instead of rewriting the entire authentication process, your application can send an authentication request through the integrated API. This API will handle the authentication process and return the result, indicating whether the user has been successfully authenticated or not. Using the authentication API from this provider saves you time and effort because you don’t need to rebuild the entire authentication system. Instead, you can leverage the authentication functionality provided through the API, speeding up the application development process and minimizing potential errors.

Using APIs also fosters collaboration between development teams and creates a flexible environment for sharing data and functionality. This promotes the development of flexible and adaptable business systems, quickly responding to market changes and user needs.

5. Standards and Protocols Related to API

API Management and Description

OpenAPI (formerly Swagger) and API Blueprint are two important tools for describing and managing APIs. Both provide detailed documentation on the structure, endpoints, and functionality of the API, helping developers and users understand how to use the API clearly and easily. OpenAPI, with its open standard, allows for creating detailed description documents with information about parameters, data formats, and how to interact with the API. In contrast, API Blueprint uses a simple and intuitive language to describe the functionality of the API without delving into technical details. Both tools help create clear API description documents, supporting effective integration, development, and maintenance of APIs.

Data Formats: JSON and XML

JSON (JavaScript Object Notation) and XML (eXtensible Markup Language) are both popular data formats used for representing and transmitting information. JSON, based on JavaScript syntax, is favored for its simplicity and readability, using key-value pairs to organize data. Conversely, XML provides higher flexibility in customizing data structure with the ability to define tags and separate structures. JSON is commonly used in modern applications due to its good interaction with programming platforms, while XML is often applied in legacy systems or when high flexibility in data structure is needed.

Data Transmission Protocols
HTTP and HTTPS are two common data transmission protocols for exchanging information between client and server over the Internet. HTTP is used to send requests and receive responses from the server, but the transmitted data is not encrypted, increasing security risks. To address this, HTTPS was developed, using SSL/TLS to encrypt data, ensuring security during information transmission. WebSocket is a protocol that allows bidirectional real-time data transmission between client and server without the need to establish new connections. This facilitates instant data updates and maintains continuous connections, suitable for applications requiring real-time data transmission such as online chat or applications needing continuous data updates. The continuity and bidirectional data transmission capability are the distinctive features of WebSocket.

OAuth and Data Authentication
OAuth and OAuth2 are two widely used authentication and authorization methods for managing access rights to data between applications and users. OAuth allows users to grant access permissions to applications without sharing passwords, instead providing unique access tokens. Its improved version, OAuth2, provides more flexible authorization and supports multiple authentication methods. JWT (JSON Web Token) is a token format used for authentication and securely transmitting information between parties. It contains JSON-encoded payload information, including user information, access rights, and expiration time, digitally signed to protect the integrity of the data. Both methods play an important role in securing and managing access rights to data between applications and users. Authenticating data through token codes, API keys, or other authentication methods helps ensure that only authorized users are allowed to access the requested data or functionality.

These standards and protocols play a crucial role in defining data transmission methods and access rights authentication, enabling secure and flexible interaction between different systems through APIs.

6. API Management and Security

6.1. Access Control and Personal Information Management

Access Control: APIs need to have clear authentication mechanisms to control who is allowed to access the service or information. Proper authorization needs to be established to ensure that each user or application only has access to the parts they are permitted to access.

Personal Information Management: APIs often transmit personal information. Therefore, compliance with data protection regulations such as GDPR (General Data Protection Regulation) is extremely important. Encrypting data, keeping personal information to the minimum necessary level, and adhering to personal information management policies are essential factors.

6.2. Protecting APIs from Attacks and Security Vulnerabilities

  • Authentication and Authorization: Utilize robust authentication methods such as OAuth, JWT (JSON Web Tokens) to authenticate users and authorize access. Implement authorization mechanisms and access token revocation between system components.
  • Encryption and Data Validation: Employ the HTTPS protocol to safeguard data transmission over the network. Encrypt sensitive data stored on servers and in databases. Validate input and output data to prevent attacks such as Injection (SQL Injection, XSS).
  • Security Testing: Conduct regular security assessments to detect and eliminate security vulnerabilities. Utilize security testing tools to identify potential vulnerabilities and enhance the system’s reliability.
  • Session Management and Monitoring: Monitor and log API activities to detect any abnormal behavior or attacks early. Session management and dual-factor authentication are also important security measures.

Protecting APIs involves not only implementing specific security measures but also requires consistency, control, and continuous updates to address increasingly complex security threats.

7. Potential Expansion and Application of APIs in the Future

APIs with Artificial Intelligence (AI) and Machine Learning (ML): The integration of APIs with artificial intelligence and machine learning will open doors to smarter applications. APIs can provide powerful data analysis, prediction, and machine learning capabilities for various applications.

Event-Driven APIs: APIs will continue to evolve towards event-driven architectures, allowing applications to react quickly to changes in the system. This may include events from IoT, real-time data, and systems capable of instant response.

Headless and Microservices APIs: Headless API architecture enables separation of the user interface from the logic and data, facilitating the development of diverse and flexible interfaces. Microservices APIs will continue to create opportunities for breaking down applications into small, flexible, and scalable services.

APIs for Internet of Things (IoT): APIs will play a crucial role in connecting and managing IoT devices, enabling the development of smart applications, from smart homes to industrial and healthcare sectors.

Socially Responsible APIs: There is a trend towards developing APIs with higher social responsibility, ensuring that data is handled fairly, safely, and respects users’ privacy.

APIs for Blockchain and Cryptocurrency: Blockchain and Cryptocurrency will create a demand for APIs to manage and interact with protocols and services within the blockchain system, from managing cryptocurrency wallets to transactions and verifying information.

The future of APIs will continue to open up many new opportunities for connectivity, integration, and innovation in various fields. The development of new standards and technologies will create more powerful APIs, supporting the development of the digital economy and smarter applications for society.