TL;DR: APIs let software systems communicate, automate tasks, and share data without exposing how each application works internally. They come in several types and architectures, including REST, SOAP, RPC, and GraphQL, and are widely used for integrations, automation, identity management, endpoint management, and AI workflows. Understanding how APIs are structured, integrated, and troubleshot helps IT teams connect tools more efficiently and resolve common errors faster.
An API, or application programming interface, is a set of rules that lets two software systems share data and functionality. It acts as a bridge between applications without exposing their internal workings.
While the idea originated in the 1940s, the API economy exploded as microservices became more popular in the 2010s. In a microservice architecture, a suite of smaller, loosely coupled services work together to act as a single application, driving digital transformation. To do this, however, those services must interact seamlessly.
We’ll walk you through the ins and outs of APIs, including how they work, what types exist, what purposes they serve, how to integrate them, and more.
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API access is available across PDQ plans, giving IT teams more flexibility to connect PDQ with the tools and workflows they already use. Use prebuilt integrations or the PDQ API to pull device and deployment data into other systems, trigger actions, automate reporting, build custom workflows, and more. Individual endpoints are available based on the capabilities included in each plan.
How do APIs work?
APIs work by defining how one software component requests data or functionality from another and how that system returns a response. For a typical web API, a client sends a request to an API endpoint, the API processes it, and the server returns the requested data, result, or error.
Pretty much anyone who knows anything about APIs will tell you they’re basically the software equivalent of a restaurant waiter taking your order, bringing it to the kitchen, and then returning to your table with the food you ordered.
The process often looks something like this:
API request: A client application sends a request to an API endpoint, sometimes through an API gateway or management layer.
API call: The API receives and processes the request, which may involve retrieving data or performing an operation.
API response: The API returns the requested data, result, or error information.
API data transfer: The response is transmitted back to the client application that made the request.
What are the types of APIs?
The term “API” is often used generically to refer to any API. But the truth is there are several different varieties. They can be broken down by management strategy and purpose.
By API management strategy
One way to distinguish APIs is by who can access them and how that access is managed. Based on their intended users, APIs are commonly categorized as public, partner, or private.
Public API: Also known as an open API or an external API, a public API is accessible to any outside developer. Some public APIs are free, but others have a subscription fee. Public APIs may still require authentication, authorization, rate limits, and other access controls.
Partner API: Partner APIs are reserved for approved business partners and typically require authentication and authorization. This gives the API owner more control over who uses the API and how they use it.
Private API: Also known as internal APIs, private APIs are used by internal software development teams to enhance productivity by connecting systems and data. They are a scalable solution that makes it easy to incorporate new systems with existing systems. Private APIs are not available to outside users, but some companies eventually make them public.
By purpose
In API-led connectivity models, APIs may also be organized into system, process, and experience layers:
System API: A system API extracts data from core systems, such as an ERP or billing system.
Process API: A process API combines data from multiple system APIs to break down data silos and improve agility.
Experience API: An experience API targets user experience by reconfiguring data based on audience and context.
By implementation
APIs can also be categorized by how they combine operations and data. One common example is a composite API.
Composite API: A composite API combines multiple API operations or data sources into a single request. This can reduce client-server round trips and simplify workflows that require data from multiple sources.
What’s the difference between remote APIs, web APIs, and web services?
A remote API communicates across a network. A web API is a remote API exposed using web technologies, commonly HTTP. Web APIs can operate over the public internet or private networks. That means that while web APIs are also remote APIs, some remote APIs are not web APIs. That said, most APIs fall into both categories.
Similarly, a web service is a type of API, but not all APIs qualify as web services. A web service is a type of API that communicates over a network using web technologies. Web services may be public, private, or restricted and can use approaches such as REST or SOAP. We’ll unpack those in the next section.
What API protocols and architectures are available ?
API architectures and protocols control what data the API shares and how it shares that information. Common API styles and technologies include REST, SOAP, RPC, and GraphQL.
REST (Representational State Transfer)
The most common API architecture. REST APIs are lightweight, scalable, and designed for simplicity.
Core principles:
Client-server separation: Clients and servers operate independently.
Stateless: Every request is self-contained — no memory of previous interactions.
Uniform interface: Standard rules govern communication.
Layered system: Intermediaries such as proxies, gateways, and load balancers can sit between the client and server without the client needing to know how the system is structured.
Cacheable: Responses can be stored to improve performance.
RESTful APIs are widely used in web services due to their flexibility and ease of integration.
SOAP (Simple Object Access Protocol)
A protocol that defines exactly how APIs exchange messages. It uses XML and often runs over HTTP.
What makes SOAP different:
Strict formatting: Every message follows a fixed XML structure.
Security standards: SOAP-based systems can use specifications such as WS-Security for message-level security, authentication, and integrity.
More overhead: Powerful, but heavier and harder to implement than REST.
SOAP is still popular in enterprise systems that require formal contracts and secure transactions.
RPC (Remote Procedure Call)
An API model that lets one system invoke a function or procedure on another system, similar to calling a local function remotely.
Key traits:
Function-based: RPC lets one system invoke a function or procedure on another system.
Multiple implementations: Common approaches include JSON-RPC, XML-RPC, and gRPC.
Use case: RPC is often used for fast service-to-service communication, including in microservice environments. Modern implementations such as gRPC can support TLS and authentication.
GraphQL
A query language and runtime for APIs that lets clients request specific data from a defined schema.
Key traits:
Query-based: Clients specify the fields and related data they need in each request.
Schema-driven: A strongly typed schema defines the data and operations available through the API.
Flexible responses: Clients can retrieve multiple related resources in a single request and avoid receiving unnecessary fields.
GraphQL is often used for applications that need flexible data retrieval, particularly when clients have different or frequently changing data requirements.
What are the uses of APIs?
The uses of APIs are limited only by your creativity. However, many businesses use them for the following purposes:
Expand reach: APIs can help their owners expand their reach and brand recognition. This is particularly true for a public API, around which an entire ecosystem of apps may spring up.
Generate revenue: While some companies offer APIs for free to build relationships, others sell an API key, creating a direct revenue stream. In some cases, APIs can also provide revenue in other ways, such as by creating a sales funnel or distribution channel.
Improve collaboration: Enterprises often rely on hundreds of cloud applications. Without APIs to connect them, information can become siloed, limiting collaboration.
Enhance efficiency and scalability: Since APIs automate data handoff between applications, employees don’t need to go through a time-consuming, error-prone manual process. API integrations can also improve scalability by simplifying the process of connecting systems and applications.
Promote innovation: Because of their flexibility, APIs support innovation. They may allow companies to connect with new business partners, launch new services, and add value.
Improve visibility: A streamlined system improves visibility into processes, allowing for better monitoring and reporting.
What are examples of APIs?
APIs are so standard that you may have utilized one today without even realizing it. While APIs have widespread uses, here are a few common instances you’re probably familiar with:
Travel booking
If you’ve ever looked up airfare on an airline’s website, you interacted with the airline’s API. You requested flight information, and the API retrieved it from the company’s database. Travel booking platforms use even more APIs to access information from multiple hotels and airlines.
Google Maps
The Google Maps API gives developers access to a wealth of geographic data, including interactive maps. Businesses often leverage this tool to give potential customers clear driving directions to their locations.
Universal logins
Many websites and apps allow users to sign in through other platforms and social media, like Google, Facebook, and Twitter. They do this by authenticating users through the services’ APIs, thereby saving users the trouble of setting up a new account and remembering yet another password.
Third-party payment processing
“Pay with PayPal” has become ubiquitous on e-commerce platforms. This API allows users to pay for items without exposing sensitive data.
How do IT teams use APIs?
IT teams use APIs to connect management and security tools, automate repetitive tasks, and exchange data between systems. APIs can help endpoint management platforms work with identity services, vulnerability scanners, cloud platforms, and other tools across the IT environment.
Common IT API use cases include:
Endpoint management: Exchange device, application, inventory, and deployment data between management platforms.
Identity and directory services: Use systems such as Microsoft Entra ID or Active Directory as sources for users, groups, devices, or targeting information.
Vulnerability management: Pass vulnerability data between scanners and endpoint management or remediation tools.
Automation: Use PowerShell or other scripting tools to retrieve data, trigger actions, and automate administrative workflows.
AI integrations: APIs can allow AI tools and agents to retrieve information from IT systems or perform authorized actions.
How do APIs support AI integrations in IT?
APIs can give AI tools controlled access to data and actions in endpoint management and other IT systems. Depending on the platform, AI integrations may use traditional APIs or newer standards such as the Model Context Protocol (MCP) to retrieve context and perform authorized tasks.
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How do you integrate APIs?
To integrate an API, review its documentation and authentication requirements, identify the endpoints and data you need, test your requests, add error handling, and monitor the integration in production.
Review the API documentation: Identify available endpoints, request methods, authentication requirements, rate limits, and response formats.
Configure authentication: Set up the required API keys, tokens, OAuth credentials, or other authentication method.
Test API requests: Verify the required endpoints and responses before connecting them to production workflows.
Handle errors and limits: Account for status codes, retries, pagination, timeouts, and rate limits.
Deploy and monitor the integration: Secure credentials, log failures, and monitor API performance after deployment.
Custom integrations
Custom integrations are developed by a skilled expert to connect existing third-party systems for greater functionality. Custom integrations can require more development and maintenance than prebuilt connectors, but they remain useful when organizations need tailored functionality.
Connector applications
Connector applications serve as intermediaries between popular software platforms via their APIs to help manage and maintain integrations. Because connector applications tend to be affordable and easy to use, they’re quite popular. They may be classified by the app or protocol they support, so you can find options like Salesforce connectors, HTTP connectors, and JDBC connectors.
Integration management platforms
API integration management platforms are typically SaaS applications used to connect other SaaS applications and cloud-based systems. With one request, they can collect and combine data from multiple sources in a single query. They act as Integration Platform as a Service (iPaaS) solutions.
What are common API errors, and how do you fix them?
For HTTP-based APIs, many errors fall into two broad categories: client/request errors and server errors. You can often determine the cause of the error and how to fix it from the HTTP status code.
Request errors
Request errors are generally client-side errors. They have 400-level HTTP status codes, such as the following:
400 Bad Request: The server can't process the request because something about the request is invalid. Check the request headers, query parameters, and body for malformed or incorrect data.
401 Unauthorized: If you’re not authenticated, you could get this error. You may need to sign up and get an API key.
403 Forbidden: The server understands the request but refuses to fulfill it, often because you don't have permission to access the requested resource or action.
404 Not Found: The server could not find the requested resource. Check the endpoint URL, resource identifier, and API documentation to make sure you’re requesting a valid resource.
429 Too Many Requests: API subscriptions often have limits per minute, per hour, and/or per day. If you exceed those limits, you may get this message. Be aware of your limits and consider adjusting your subscription if necessary.
Server errors
If you see a 500-level HTTP status code, you’re probably experiencing a server error. You may need to contact API support to resolve the issue.
500 Internal Server Error: The server encountered an unexpected condition that prevented it from completing the request. Check the API documentation and service status, and retry or contact support if the error persists.
501 Not Implemented: The server does not support the functionality required to fulfill the request. Check the API documentation to confirm that the requested capability or HTTP method is supported.
502 Bad Gateway: A gateway or proxy received an invalid response from an upstream server. The problem is generally server-side, so retry the request or check the service status.
503 Service Unavailable: The server is temporarily unable to handle the request, often because of overload or maintenance. Try again later and honor a
Retry-Afterheader if the API provides one.504 Gateway Timed Out: A gateway or proxy did not receive a timely response from an upstream server. Retry the request and check the service status if the problem persists.
APIs are the unsung heroes behind the digital tools we rely on every day. Whether you're connecting systems, automating tasks, or just trying to fix a mysterious 401 error, a solid grasp of API fundamentals can save you time and sanity.
If you're looking to dig deeper into the tech that powers your environment, check out our Sysadmin Glossary for quick-hit definitions on everything from ACLs to XML. And if you ever hit a wall, the PDQ community is always a good place to trade tips, troubleshoot, or just swap war stories.
