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Types of API

Explore the wide world of APIs with our comprehensive Types of API guide. Learn how various interfaces, including REST and SOAP, GraphQL, and gRPC, promote digital innovation across industries. Understand their protocols, architectures, and real-world applications before choosing the best API for your projects. Ideal for developers and businesses looking to use API technology to improve connectivity and functionality.

Written byArman
Published OnFri Jun 04 2021
Last UpdatedTue Feb 20 2024

In the digital age, Application Programming Interfaces, or APIs, are the foundation for software communication. They allow different applications to communicate, share data, and easily perform tasks. Developers may interact with other software applications using predefined functions through an API, which creates a set of guidelines and standards for creating and integrating application software.

APIs, like any other concept in software development, have different types. Developers build APIs for various purposes using different technologies and programming languages and follow different architectural styles, which result in entirely different kinds of APIs. To learn more about APIs, we highly recommend the What is API article.

This post will explore the world of APIs and give you a good understanding of the different types of APIs, API protocols and architectures and so on. Whether you’re planning to develop an API or curious about APIs in general, this post has something for you, so without further ado, let’s get started.

Understanding the Main Types of APIs

APIs are divided into four main categories based on their intended user base and accessibility:

Open APIs (Public APIs)

Open APIs, often known as Public APIs, provide developers and other users with little limitations. They are intended to be publicly accessible in order to facilitate the development of services and applications that can interact with the original platform.


  • Twitter API: Allows developers to access Twitter’s functionalities, including posting tweets, reading user profile data, and more.
  • Google Maps API: Allows you to integrate Google Maps on webpages with customisable views and annotation.

Pros and Cons

  • Pros: Developers may easily access it, allowing for widespread application creation and innovation. They promote both community and third-party development.
  • Cons: They may lack advanced security features, making them more vulnerable to abuse. Because of their open nature, public APIs may result in higher maintenance costs.
Wide accessibilityPotential for misuse
Encourages innovationHigher maintenance costs
Fosters community developmentMay lack advanced security features

Partner APIs

Partner APIs are available to specific parties who have entered into a partnership with the provider. These APIs are not available to the general public and require specific permissions to access.


  • Amazon MWS (Marketplace Web Service): Allows Amazon sellers to exchange data on listings, orders, payments, reports, and more.
  • Salesforce API: Provides access to Salesforce’s platform for CRM and other business management functionalities, available to Salesforce partners.

Pros and Cons

  • Pros: Provide more controlled access to ensure data security and integrity. They facilitate strategic business partnerships and integration.
  • Cons: Limited accessibility might limit innovation and usage. The requirement for certain rights or licenses might also slow down the development process.
Enhanced security and controlRestricted access limits external innovation
Enables strategic partnershipsRequires rights or licenses, which can be a barrier

Internal APIs (Private APIs)

Internal APIs are used by organizations to improve their internal products and services. These APIs make it easier to integrate and communicate amongst various internal systems, which boosts efficiency and productivity.


  • Internal HR systems: APIs that allow companies to efficiently manage payroll, benefits, and employee records by integrating multiple HR platforms.
  • Inventory management systems: APIs that connect a company’s inventory system to its sales and logistics platforms to improve efficiency and streamline operations.

Pros and Cons

  • Pros: Increase internal productivity by enabling smooth integration and communication among various internal systems. They can be greatly customized to an organization’s requirements.
  • Cons: Restricted to internal use, limiting external innovation. Requires significant investment in internal development and maintenance.
Customized for specific organizational needsLimited to internal use; does not benefit the wider community
Enhances internal productivity and efficiencyRequires investment in development and maintenance

Composite APIs

Composite APIs combine multiple operations into a single API call. These APIs are useful for executing a sequence of tasks, making processing more efficient and decreasing server load.


  • Payment processing systems: An API that processes a payment, updates the order status, and sends a confirmation email to the customer simultaneously.
  • Flight Booking Systems: A composite API that handles seat selection, payment processing, ticket issuance, and sending confirmation details, all within a single request to streamline the customer’s booking experience.

Pros and Cons

  • Pros: Efficiently handles numerous operations and services with a single call, reducing server load and improving listener performance in web interfaces.
  • Cons: Complexity in management and potential dependency issues if one of the integrated APIs changes or becomes unavailable.
Reduces the number of API calls, improving efficiencyComplexity in management and potential for dependency issues
Enhances performance of web interfacesCan be difficult to debug due to multiple integrated services

API Protocols and Architectures

APIs are built on various protocols and architectures, each serving specific needs:

REST (Representational State Transfer)

REST is an architectural style that use a stateless communication protocol, typically HTTP. It treats data and functionality as resources that may be accessed via the usual HTTP methods (GET, POST, PUT, and DELETE).

Pros and Cons

  • Pros: Uses standard HTTP methods, making it easy to implement and understand. It is stateless, which means that each request sent from client to server must include all of the information required to understand the request. Supports caching, which reduces the need for repeated data transfers.
  • Cons: REST APIs can sometimes struggle to handle large amounts of data and stateful operations. The lack of a strict standard can result in inconsistencies in implementation.
Simplicity and flexibilityCan be less secure without proper implementation
Wide usage and compatibilityCan lead to inefficient data retrieval (over-fetching/under-fetching)
Scalable and easy to integrateStatelessness might require additional handling for session management

SOAP (Simple Object Access Protocol)

SOAP is a protocol for transferring structured data during the deployment of web services. It encodes messages with XML and negotiates and transmits them using various application layer protocols, primarily HTTP or SMTP.

Pros and Cons

  • Pros: High security with built-in error handling makes it appropriate for enterprise-level applications. It follows a strict standard, ensuring consistency across different implementations.
  • Cons: Its extensive use of XML can make it complex and heavy, resulting in higher payloads and slower processing times. It is less flexible than REST.
High security (WS-Security standards)More complex than REST
Extensive standards supportHeavyweight due to XML verbosity
Reliable message delivery (WS-ReliableMessaging)Lower performance and scalability


Facebook (Meta) developed GraphQL, a runtime and query language for APIs that executes queries using a type system defined for your data. It is useful for complex systems with many entities since it allows customers to request only what they need.

Pros and Cons

  • Pros: Clients can request exactly what they need, reducing data overfetching and underfetching. Its high efficiency and flexibility make it ideal for complicated systems and real-time data applications.
  • Cons: It requires a considerable learning curve and early schema design, which can be time-consuming. When queries are not properly managed, their complexity might have an influence on performance.
Fetching exactly what’s needed reduces over-fetchingComplex queries can impact server performance
Allows rapid feature developmentRequires a significant learning curve and initial setup
Real-time data with subscriptionsCustom caching mechanisms might be needed

gRPC (Google Remote Procedure Call)

Google developed gRPC, a high-performance, open-source universal RPC framework that uses HTTP/2 for transport, Protocol Buffers for interface description language, and has capabilities such as authentication, load balancing, and more. gRPC is used for internal communication between microservices, focusing on speed and efficiency.

Pros and Cons

  • Pros: Its usage of HTTP/2 and Protobuf (a lightweight binary format) provides high performance, particularly in microservices architectures. Supports streaming and is language-independent.
  • Cons: Relatively new, having a smaller ecosystem than REST and SOAP. The binary protocol can be more difficult to debug and inspect than JSON or XML.
High performance and efficiencyRelatively new, with fewer resources and community support
Supports bi-directional streamingNot as human-readable as JSON over HTTP
Language agnostic with strong type-checkingRequires the use of Protocol Buffers

Comparison of API Protocols

ProtocolData FormatUse CasesAdvantages
RESTJSON, XMLWeb Services, Public APIsFlexible, Wide Adoption, Scalable
SOAPXMLEnterprise-level ApplicationsHigh Security, Reliable Messaging
GraphQLJSONComplex Systems, Real-time DataEfficient Data Retrieval, Flexible Queries
gRPCProtobufMicroservices, High-PerformanceCompact, Fast, Supports Streaming

Selecting the Right API

Choosing the proper API for your project is critical for its success. Here are factors to consider when selecting an API:

  • Compatibility and Integration: Ensure the API integrates well with your existing systems and meets your technical requirements.
  • Functionality: Evaluate whether the API provides the specific functionalities you need for your project.
  • Performance and Scalability: Consider the API’s response time and ability to handle load increases, especially if you expect high traffic.
  • Security: Look for APIs that offer robust authentication and encryption to protect sensitive data.
  • Documentation and Support: Well-documented APIs with active support communities can significantly reduce development time and troubleshooting efforts.
  • Cost: Determine the cost of using the API, including any subscription fees or usage limits.


APIs are an essential part of modern software development, providing many possibilities for developing scalable, connected, and efficient applications. Developers and businesses can use the power of APIs to improve their services and offer better user experiences by knowing the different types of APIs, their protocols, and their uses across industries.

Frequently Asked Questions

We got an answer for your questions

  • What is an API, and why is it important?

    An application programming interface (API) is a collection of rules that enable various software applications to communicate with one another. APIs are critical for developing modern software because they allow developers to integrate and use external services without having to create those features from scratch.

  • What are the main types of APIs?

    The four main types of APIs are Open APIs (Public APIs), Partner APIs, Internal APIs (Private APIs), and Composite APIs. Each serves different access levels and purposes, from public accessibility to specific partner usage and internal integration within organizations.

  • How do REST and SOAP APIs differ?

    REST APIs are well-known for their simplicity and versatility, as they manage data through HTTP requests. They support various data formats and are stateless. SOAP APIs, on the other hand, are protocol-based, heavily standardized, and utilize XML for messaging, offering higher security and reliability for enterprise-level applications.

  • What is GraphQL, and how does it compare to REST?

    GraphQL is an efficient query language for complicated systems because it lets clients request the specific data they need from APIs. GraphQL queries are customized to the unique requirements of the client, in contrast to REST, which uses predefined endpoints, therefore minimizing over- and under-fetching problems.

  • What considerations should be made when choosing an API?

    When selecting an API, consider the specific requirements of your project, the programming language and environment you're using, the amount of security required, and the API's scalability. It's also important to evaluate the ease of integration, documentation quality, and the community or support available.

  • How are APIs used in different industries?

    APIs find applications across various industries, facilitating tasks like financial transactions, social media interactions, content delivery, authentication processes, and more. They provide for smooth integration and data exchange between different systems, improving functionality and user experience in applications such as banking apps, social platforms, and e-commerce websites.

  • What is a legacy API?

    Legacy API is a term used to describe an API that users are using for many years. Often the term legacy means there will be a successor API to replace the Legacy API.

  • What makes an API legacy?

    APIs become legacy for many reasons but primarily because of using programming languages that are not popular anymore, using technologies in maintenance mode and sometimes because of poor design decisions.

  • What API versioning means?

    Versions are a common practice when building REST APIs. Versioning allows software teams to introduce new features to their API without causing issues for existing users who use the API. Instead of changing existing endpoints, software developers introduce new endpoints for new features.

  • What Open APIs are currently available?

    Open APIs are available for different topics. To get an idea, please have a look at this page (

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