API integration: here’s everything you need to know

As you look to integrate your applications and build data flows across them, you’ll likely look to use application programming interfaces (APIs).

The reasons for doing so aren’t hard to discern: APIs can sync data in frequent intervals; they offer reliability (changing an application’s UI, for instance, shouldn’t break an API connection); they can provide a secure connection, and much more.

To help you make the most of API integrations, we’ll cover everything you need to know about them—from how they work to common use cases to the 3rd-party solutions you can use.

But to get us started, let’s align on how APIs work.

What is an API?

An API provides a specific set of rules and protocols for how applications can communicate with one another. 

In basic terms, a client application makes an API call to an endpoint in another application’s server. Assuming the call is formatted correctly and includes the appropriate permissions, the server provides a response to the client that includes the requested information.

A visual breakdown of API integration

There are different types of APIs, and each dictates how API calls need to be made and the way responses are structured. The two most common ones are a simple, access, object, protocol (SOAP) API, and a representational, state, transfer (REST) API—with the latter being most common.   

Related: How APIs and SFTP differ

What is an API integration?

It’s the process of using APIs to connect applications. This includes connecting the applications you use within your organization and connecting your product with any 3rd-party applications.

The two different scenarios of API integration

Related: What is REST API integration?

API integration examples

Here are some examples of API integrations you can build internally as well as externally:

1. Enrich new leads automatically

As your marketing team collects and nurtures leads, they’ll likely need to collect additional information on each to accurately assess their fit with your organization’s product or service.

With this in mind, you can connect your data enrichment tool (e.g. Clearbit) with your marketing automation platform (e.g. Marketo) and build a workflow where once a lead is created in the marketing automation tool, it’s automatically enriched. The additional information the data enrichment tool finds—such as company size, industry, or a contact’s job title—gets added to the appropriate fields within the prospect’s profile in your marketing automation solution, enabling marketing to leverage the data easily and quickly.

2. Add signed offer letters to your ATS with minimal friction

Recruiting will want to learn when a candidate signs their offer letter so that they—and their colleagues in HR—can begin the process of onboarding them.

To help recruiting discover these moments without leaving their applicant tracking system (ATS), you can integrate your e-signature platform (e.g. DocuSign) with your ATS (e.g. Greenhouse) and build a workflow where any fully-executed contract is added to the associated candidate’s ATS profile.

3. Connect to CRM solutions to help sales reps use your data more easily

Imagine you offer a sales automation solution that provides intelligent recommendations to sales reps on the organizations they should reach out to. 

To help your clients’ sales reps determine whether recommended leads already exist in your CRM and to ensure new leads get added to your CRM seamlessly, you can connect to the CRM solutions your clients use. These product integrations can seamlessly sync all of the lead data your clients’ sales reps care about, all but ensuring your product fits naturally within the reps’ day-to-day workflows.

API integration benefits

Here are just some of the benefits of API integration:

Prevents human errors

Manually-intensive tasks, like reentering data across applications, can lead to costly mistakes that harm your business and your clients’. For instance, if a sales rep is keying in details on a lead in your CRM, they may type in the wrong company name, leading the rep to make an embarrassing mistake later down the line that can harm your organizations’ reputation and lower the rep’s chances of winning over the prospect.

Since API integration allows data to flow freely across applications without human intervention, employees can avoid performing these error-prone tasks and the issues they can cause.

Improves the employee experience

Manually-intensive activities aren’t just ripe for making mistakes—they’re also unpleasant to perform. Fortunately, API integrations can handle many, if not most, of them, allowing employees  to focus on the more strategic, thoughtful tasks they enjoy, instead.

Lets you build high-performing integrations

APIs can meet the performance requirements you’re looking for from your integrations. They’re more resilient than other approaches to integration, like connecting applications at the UI-level; they can sync data in near real-time; and they’re likely available across the applications you want to connect and the data you need to access.

Note: The benefits below pertain exclusively to product integrations. 

Elevates your competitive positioning

As prospects evaluate you against your rivals, they’re likely considering a range of criteria—and integrations is likely one of them. 

With this in mind, offering more integrations than your competitors should, all else equal, increase your chances of winning competitive sales.

Increases your customer retention rate

Once prospects begin adopting your integrations, they’ll likely be able to use your product in more valuable ways and leverage the data your application provides in their other systems more effectively. Both of these factors should improve customer satisfaction and, eventually, retention.

Related: Top API integration solutions

Challenges of API integration

Unfortunately, API integrations can come with drawbacks. Here are a few to be aware of:

Consumes your developers' time

The process of building integrations in-house (i.e. native integrations) can be extensive for your developers. For each integration, they’ll need to read through and understand the vendor’s API documentation, design the APIs, test them, and, once implemented, oversee and maintain them. 

Given that your organization is likely looking to build several integrations over time, your engineers can become fully consumed in developing and maintaining the integrations at the expense of building out and improving your core product.

Expensive to build and maintain in-house

The engineers who can build and maintain integrations at your organization are likely to command a relatively high salary. 

When you consider that a single integration can keep several of these engineers fully occupied, it becomes clear that the return from the integrations can become murky, if not too low to justify the investment in resources.

Related: Challenges of point-to-point integrations

Opens your organization up to risks

Relying on select engineers to build and maintain the integrations could lead to issues down the line when they leave.

The remaining engineers may not understand the coding language that was used to build an integration, know where it lives, or even be aware that it exists—all of which make the prospect of enhancing and maintaining the integration difficult.

API integration platforms

To help you address the challenges above while still reaping the benefits of API integrations, you can look to build integrations via a 3rd-party

We’ll break down some of your options for internal and customer-facing integrations:

API integration solutions for applications used internally

Here are some of your options for the applications you use in-house:


An integration platform as a service (iPaaS) lets you build integrations between SaaS applications, databases, files, and on-prem systems and develop data flows that work across them. 

A visual illustration of iPaaS

The platform can help accelerate integration and automation development through its library of pre-built connectors and automation templates. It lets you track the performance of your integrations and automations at a high level. And it offers platform bots that can communicate between your applications and your business communications platform (e.g. Microsoft Teams). 

That said, the platform has drawbacks: It only allows you to build integrations one at a time. And, despite branding itself as a low-code/no-code solution, it often requires technical expertise to use. This can ultimately force your developers to use the platform to build and manage the integrations and automations themselves.


Robotic process automation (RPA) software traditionally uses software scripts (referred to as bots) to perform manual tasks across documents, applications, emails, etc. Mmany RPA platforms can also provide API-based integrations.

However, RPA software’s API integration capabilities are, in all likelihood, less robust than that of iPaaS solutions; RPA vendors have likely invested less time and fewer resources on developing their API integration capabilities. 

API integration solutions for customer-facing applications

Similar to the section above, there are likely two solutions you’re evaluating:

Embedded iPaaS

An embedded iPaaS is an iPaaS that can be added to your product in a few different ways. 

Your team can implement and maintain the integrations themselves and simply allow clients to benefit from them; allow clients to build and maintain the integrations inside of your product—or a combination of both approaches.

Like iPaaS, an embedded iPaaS forces users to build integrations one at a time, requires technical expertise to use, and fails to provide comprehensive integration management capabilities. Taken together, users will struggle to integrate at scale and maintain the integrations effectively. 

Unified API platform

A unified API solution—or a universal API solution—offers a single, aggregated API that, once built to successfully, lets you offer multiple integrations in a given software category (like ATS or CRM).

A visual illustration of a unified API solution

Unified API platforms neatly address the issue of scalability, but not all unified API vendors are created equal. 

Merge, the leading Unified API platform, stands out by offering hundreds of integrations across key unified API categories, including file storage, ticketing, CRM, marketing automation, HRIS, ATS, and accounting. The platform also provides comprehensive common models so that users can access all the data they need (along with advanced features to access data beyond the common models); and it provides robust integration management capabilities so you can help clients identify and resolve any integration issue quickly and easily.

Learn more about Merge by scheduling a demo with one of our integration experts.