API (Application Programming Interface)

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What is application programming interface (API)?

An application programming interface (API) is a set of rules that enable two software systems to communicate. It defines methods and functions that one system can use to interact with another. Essentially, APIs allow software to share data and perform tasks seamlessly.

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For instance, a website might use an API to fetch data from a database. Similarly, a mobile app could access cloud-based services via an API. These interactions simplify software development and make applications more efficient.

In HR and talent management, APIs connect core systems such as assessment platforms, applicant tracking systems, and HRIS tools : allowing data to flow seamlessly without manual entry. Understanding API fundamentals helps HR leaders make informed decisions when selecting tools that integrate cleanly into their talent acquisition stack.

APIs are designed for different programming languages and platforms. They often rely on open standards like the Hypertext Transfer Protocol (HTTP) to facilitate communication. APIs can be internal (used within an organization) or external (made available for third-party developers). Whether on the client side or the server side, APIs play a vital role in how software systems work together.

API protocols

APIs are built on various protocols, each offering unique benefits. According to HBR’s technology and analytics research, organizations that master API integration gain significant competitive advantages through faster, more connected workflows. Common API protocols include:

  • HTTP (Hypertext Transfer Protocol): This protocol enables communication between a client (like a web browser) and a web server. It’s widely used to send and receive requests and responses. APIs rely on HTTP methods (GET, POST, PUT, DELETE) to define actions at an API endpoint.
  • REST (Representational State Transfer): REST is an architectural style for designing APIs. REST APIs use HTTP, are stateless, and offer scalability. Their simplicity and flexibility make them popular among web developers.
  • SOAP (Simple Object Access Protocol): SOAP APIs exchange structured data in distributed systems. This protocol works with XML and is often used in remote procedure calls (RPC) for accessing resources.
  • gRPC (Google Remote Procedure Call): This open-source framework uses HTTP/2 and Protocol Buffers for communication. gRPC handles large data transfers and high-concurrency environments efficiently.

Types of apis

APIs come in various forms. SHRM’s HR technology guidance highlights API-connected HR platforms as essential for modern talent management. Common types include:

  1. Open APIs (Public APIs): These application programming interfaces are accessible to anyone. They allow developers to build integrations and extend the functionality of existing systems.
  2. Internal APIs (Private APIs): These are hidden from the public and used within an organization. They enable seamless communication between internal systems.
  3. Partner APIs: These application programming interfaces are shared with specific developers or partners. They often support collaboration or limited access to resources.
  4. Composite APIs: These APIs combine multiple services or data structures into a single interface. They simplify processes and improve efficiency.

Frequently asked questions

API stands for Application Programming Interface. It is a defined set of rules, protocols, and tools that allows different software applications to communicate with each other. Think of it as a menu at a restaurant : the menu tells you what you can order, and the kitchen (the system) delivers the result.

REST (Representational State Transfer) is a lightweight, stateless architectural style that uses standard HTTP methods (GET, POST, PUT, DELETE). It is flexible, fast, and widely used for web and mobile applications. SOAP (Simple Object Access Protocol) is a more rigid, XML-based protocol used in enterprise environments where strict security and formal contracts are required, such as banking or healthcare integrations.

APIs allow HR platforms to share data with each other : for example, an ATS might use an API to push accepted candidate data directly into an HRIS, or a pre-employment assessment platform might send results to a hiring dashboard via API. This eliminates manual data entry, reduces errors, and creates a seamless, integrated HR technology stack.

An API endpoint is the specific URL or address where an API receives requests. Each endpoint corresponds to a particular function : for example, /employees might return a list of employees, while /employees/123 returns data for a specific employee. Endpoints define what data or actions are available through the API.

APIs can be secure if implemented correctly. Common security measures include API keys, OAuth 2.0 authentication, rate limiting, HTTPS encryption, and input validation. However, poorly secured APIs are a frequent vector for data breaches. Organizations using HR APIs should ensure all integrations comply with their data privacy policies and security standards.

Public (open) APIs are available to any external developer and are often used to build integrations or third-party apps. Private (internal) APIs are accessible only within an organization and are used to connect internal systems. Partner APIs sit in between : shared with specific trusted partners under controlled access agreements.