What Is API and How Does It Work?

ByNeelabja Adkuloo


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Do you own a wireless speaker?

When you turn it on, chances are your mobile gets paired to it instantly. That’s because an API integrates your speaker with your cell phone, enabling the wireless feature.

But wait, how does an API work? Read our guide to understand how APIs, which are essential to building apps, function.

Table of contents

What is an API?

An API or Application Programming Interface is a facilitator that enables apps, databases, softwares and IoT devices to communicate with each other, without which they won’t be able to interact. It's a set of tools and protocols used by developers to build user-friendly software apps.

But how, you may ask?

how does an api work?

  • A series of commands by the end-user allows your app to interface with an external software via an API. The interface refers to the endpoints at which various software components can communicate.

  • Endpoints specify where the resources that can be accessed by third-party software are located. Typically, access is gained through a URL to which HTTP requests are sent and from which responses are anticipated.

  • Users interact with user interfaces, which are the graphical elements of a software. They're how you got to this particular screen. Of course, there is a lot of code on the backend.

You can write APIs in various programming languages, including Python, Ruby, Java, JavaScript, and Perl.

Why use an API gateway?

Here are 6 reasons why you should use API to integrate web-based devices and applications:

  • Simplify app development

Developers can add unique functionalities to their applications using an API to make app development easier, saving both time and money. APIs also enable flexibility, simplify app and email design, and generate chances for innovation when creating new tools and products or managing current ones.

  • Ease of collaboration

APIs help business and IT teams collaborate by making it easier for developers to integrate new application components into an existing architecture.

  • Integrate third-party tools and apps

Allowing consumers to access data using an API lets you integrate third-party apps. So long as the API's behavior remains unchanged, you can modify its internal systems without affecting your customers.

  • Make data more secure

You can secure user data by determining the identity of your end-user and identifying the resources they can access. For example, in a REST API, basic authentication can be implemented using the TLS protocol, OpenID Connect or OAuth 2.

  • Trigger automated email campaigns from third-party apps

third party apps

You can set trigger endpoints for journey emails using Mailmodo REST API and trigger automated campaigns from any external platform, including Zapier, Integromat, etc. For instance, you can send emails personalized to a specific event segmented based on event properties using a custom event API.

  • Monetize your data

Public APIs add a unique value to your business by helping you monetize your data. How so? Let’s assume you’ve created an app that enables users to find books they want using a publicly available API. You can leverage the API to make more sales or generate other business opportunities.

Google Maps API is another great example of monetized public API. Let’s take a look at other well-known examples of API.

Application and usecase of API

Application Use Case
Mailmodo You can send transactional AMP emails using Mailmodo REST API. Upon enabling a transactional email api, you get the trigger endpoint URL.
Google Map Let’s say you want to add a map to your website. You can’t access Maps directly since the code that powers it is stored on Google server. Google provides an API that allows users to download the map.
Google Nest Google Nest uses an API to save energy by adjusting the temperature on a thermostat.
Google Weather Google gets weather data from elsewhere to keep its Weather app updated. It uses an API that feeds it recent weather information in a format the app can alter.
Facebook When a user clicks the log-in button, a pop-up appears asking them to confirm they want to log in. When the user approves, the API sends identity information to FB, allowing it to identify who is logging in.
Paytm Paytm sends an order request to the Paytm API when the user selects the Pay with Paytm button. The user is authenticated and their purchase is confirmed. Finally, the API returns payment confirmation to the app.
Airbnb Airbnb collects airline and hotel availability from providers using a third-party API. Similarly, if you make a reservation, an API will be used to confirm the trip with the provider from whom it was sourced.

Types of APIs

APIs can be available privately, publicly, in partnership or for commercial usage. They can also be classified as per the systems they’re designed, including operating systems, databases, remote access or web-based. We’ve talked about each one in detail below:

  • Private API

In-house developers can use private APIs to integrate a company's IT systems or applications. Even if the apps are made public, the interface is only accessible to individuals who work with the developers. This strategy gives a business complete control over API usage.

Pro tip: You should consider interface stability when an API is made public. Changes to the API, such as adding more parameters to any function, could break compatibility for clients who rely on it.

  • Public API

All open or public APIs features are accessible to the general public and can be used without restriction. The API-related documentation must be publicly available, and the API can be freely used to develop and test applications. Google Maps is a perfect example.

  • Commercial API

Subscribers to commercial APIs pay a fee to use it. Free trials are a typical strategy used by API publishers to allow customers to test APIs before purchasing subscriptions. For instance, Weather Underground is a commercial API that sells access to its weather data API.

  • Partner API

Partner APIs are only shared with business partners who have signed a contract with the API publisher. Software integration between two companies is a prominent use case for partner APIs. An example of a partner API is eBay’s API.

  • Database API

Database APIs allow an app to communicate with a database management system. Developers work with databases by writing queries to retrieve information, change tables, etc. An example is ORDS database API used by Oracle REST Data Services.

  • Operating Systems API

Operating Systems API specifies how programmes interact with operating system resources and services. Each operating system has its own set of APIs, such as the Windows API or the Linux API.

  • Remote API

Using a remote API, two distant applications communicate across a communications network, primarily the internet. Two examples of remote application programming interfaces are the Java Database Connectivity API and the Java Remote Method Invocation API.

  • Web API

Web APIs allow machine-readable data and functionality to be transferred between client-server architecture. These APIs mostly use Hypertext Transfer Protocol (HTTP) to transmit requests from apps and responses from servers. An example is Mailmodo’s REST API, a type of API protocol.

API protocol types

To use APIs, we must adhere to specific procedures. A protocol specifies the rules for API calls. An API call is a message sent to a server requesting an API to provide information or a service. Let's look at some of the most used API protocols:

  • REST

Representational State Transfer (REST) APIs are used by apps like Uber, Amazon, and Netflix. You must follow the following requirements for a REST API:

  • Unique Resource Identifiers, Create, Read, Update, Delete, and JavaScript Object Notation protocols should be used to communicate between a client and a server over HyperText Transfer Protocol or HTTP.

  • Changes made by a user should not influence the server and vice versa.

  • Caching client responses makes them faster and more efficient, which improves the user experience.

  • The API should support a layered design, with each layer contributing to a defined hierarchy. REST uses a layered-system architecture where you deploy the API on server A, save data on server B and authenticate API requests on Server C.

  • SOAP

SOAP or Simple Object Access Protocol is a well-known protocol that, like REST, operates as a type of Web Application Programming Interface. According to Microsoft, which created SOAP, it enables the communication between systems over HTTP or the Simple Mail Transfer Protocol (SMTP) for email transfer.

Payment gateways, identity management, CRM systems, and banking and telecommunication services all favor SOAP APIs. One of the most renowned SOAP APIs is PayPal's public API.

  • RPC

The RPC protocol is used to make a remote procedure call. They are the most basic and earliest Application Programming Interfaces available. An RPC's purpose was to allow a client to run code on a server.

  • GraphQL

GraphQL enables the client to specify the data they require and simplifies data aggregation, allowing the developer to make only one API call to get all the information they require.

Apps that use GraphQL like Yelp, Shopify, GitHub, and Coursera have more control over the data they need from a server, allowing them to function quickly even when the mobile connection is slow.

How does an API work?

The following are some of the use cases of APIs in Mailmodo:

  • Trigger transaction emails on user actions like sign up or purchase in Mailmodo.

  • Trigger email journeys from an external app.

  • Import contacts in Mailmodo from your software.

  • Export data from email campaigns.

  • Use emails to send dynamic forms.

Let’s consider one use case i.e. triggering transactional emails in Mailmodo and see how the REST API works.

Step 1: Visit the transactional page.

transactional page

Step 2: Click on the ‘New Transactional Campaign’ button.

New Transactional Campaign button

Step 3: Choose the email template and select ‘Next’.

Choose the email template

Step 4: Add the details of the campaign and select ‘Next’ to trigger it via API.

Add the details of the campaign

Step 5: Click on the ‘Rest API’ option and select ‘Next’.

Click on the ‘Rest API’ option

Step 6: Review your campaign and select ‘Enable the Campaign’ to get the campaign ID which is your API endpoint.

get the campaign ID which is your API endpoint

Step 7: Select ‘Copy URL’ and paste it into your system to complete setting up the transactional campaign.

Wrap up

Sending AMP or HTML transactional emails with Mailmodo's REST API can be done easily, quickly and efficiently. Take inspiration from our guide on 17 AMP email examples to create an interactive email experience with API integration today.

What you should do next

Hey there, thanks for reading till the end. Here are 3 ways we can help you grow your business:

  1. Talk to an email expert. Need someone to take your email marketing to the next level? Mailmodo’s experts are here for you. Schedule a 30-minute email consultation. Don’t worry, it’s on the house. Book a meet here.

  2. Send emails that bring higher conversions. Mailmodo is an ESP that helps you to create and send app-like interactive emails with forms, carts, calendars, games, and other widgets for higher conversions. Get started for free.

  3. Get smarter with our email resources. Explore all our knowledge base here and learn about email marketing, marketing strategies, best practices, growth hacks, case studies, templates, and more. Access guides here.

API related FAQs

No, an API (Application Programming Interface) is not a programming language. It is a set of rules and protocols that allows different software applications to communicate and interact with each other. APIs define how different software components should interact, but they are not a programming language themselves.

APIs can be written in various programming languages depending on the technology stack and requirements. Commonly used languages for building APIs include Python, Java, JavaScript, Ruby, and C#. The choice of language depends on factors such as the platform, performance, compatibility, and the specific needs of the API implementation.

The choice of language for creating APIs varies based on the technology stack and project requirements. However, some of the commonly used languages for developing APIs are Python, Java, JavaScript (Node.js), Ruby, and C#. These languages have robust frameworks and libraries that facilitate API development.

API is a set of rules for software communication, while an interface defines methods and properties required to fulfill a contract. API is broader, encompassing communication rules, authentication, and data formats. The interface focuses on specific methods/properties. API includes interfaces and more elements.

What should you do next?

Thanks for reading till the end. Here are 3 ways we can help you grow your business:


Get smarter with our email resources

Explore our email marketing guides, ebooks and other resources to master email marketing.


Do better email marketing with Mailmodo

Send app-like interactive emails with forms, carts, calendars, games, etc. to boost email ROI.


Talk to an email expert

Get a 30-min. free email consultation with a Mailmodo expert to optimize your email marketing.

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