API vs middleware: how to distinguish between the two

Application programming interfaces (APIs) and middleware are key topics within the realm of integration and automation, but they’re often treated as one and the same when, in reality, they represent entirely different concepts.

We’ll break down their differences by explaining each topic and by comparing them directly. 

What is an API?

An API consists of a specific set of rules and protocols that allow applications to communicate with one another. Its purpose is to help disparate applications keep data in sync so that users can access accurate, up-to-date information within the applications they rely on.

Related: APIs vs integrations

The anatomy of an API call 

Generally speaking, an API request includes two parties: a requestor (referred to as the “client”) and a responder (referred to as the “server”, since the responding application receives, processes, and completes API requests from their server). 

The requestor makes a specific HTTP request over a network connection—GET, PUT, PATCH, POST, or DELETE. The request also includes the endpoint, or resource, the requestor cares about; authentication information (e.g., API key) to confirm that the requestor has the appropriate set of permissions; and additional information within the header and/or body to help the requestor clarify the data they either want to receive or add, along with that data’s format.

Once the server receives and processes the request, it returns metadata in the response header—such as the response’s status code—and the requested data in the body. 

A visualization of an API call

Examples of APIs

There are countless examples of APIs. Here are just a few that can help clarify our conceptual overview above.


The spend management platform offers a robust and diverse set of APIs for integration developers. 

For instance, you can retrieve information, like the details on corporate cards employees have;  or create/update information in Ramp, like creating or updating a virtual card for a specific employee.

Just a few resources Ramp includes in their REST API

Related: Examples of API-based integrations


The CRM solution allows you to retrieve, add, and update a wide range of data through its API. For example, you can get attachments from specific opportunities in the application; and you can update the status of a given lead in the application.

A screenshot of various resources you can fetch from Insightly's Leads resource
Your application can access a wide range of data through Insightly’s “/Leads” endpoint

What is middleware?

It’s a 3rd-party tool that lets you develop and maintain integrations. These integrations are often built via APIs and can apply to one of two scenarios—integrating your internal applications or connecting your product with the 3rd-party applications your prospects and clients use. 

The two types of integrations that middleware tools can help you build and maintain

Related: Comparing flat file integration with APIs

Examples of middleware 

Depending on whether you’re looking to build internal or customer-facing integrations, you’ll likely come across different sets of integration middleware.

Let’s review a popular middleware tool for each of these categories.


Workato offers an integration platform as a service (iPaaS) that lets you develop integrations through their pre-built applications connectors and their “recipe”-builder interface. 

While they also offer an embedded iPaaS solution for customer-facing integrations, Workato is best suited for internal use cases since their platform comes with a long learning curve and forces you to build one integration at a time.


Merge is a single API that lets you add hundreds of integrations to your product across key software categories; the list includes CRM, file storage, HRIS, ATS, ticketing, accounting, among others.

Illustration of a unified API

Merge also offers Integration Observability, which is a suite of features that allow your customer-facing team to maintain clients’ integrations; and, through its partner engineers, the company maintains the integrations on your engineering team’s behalf.

You can learn more about Merge by scheduling a demo with one of our integration experts.

In case you have any lingering confusion on the differences between middleware and API, we’ve compared them directly below. 

Middleware vs API

An API is a method of connecting applications with one another, while middleware is a 3rd-party tool that can support this method, among others—like webhooks or file transfers.