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Blog • Developer | eCommerce

An Introduction to eCommerce APIs

Last updated: 12 Sep 2019

In this post we’ll cover what an eCommerce API is, why you should use one and how you should evaluate an eCommerce API.


At a higher level it may help to understand what an API is before we narrow down on what an eCommerce API is.

The official description of what an API is:

"An application program interface (API) is a set of routines, protocols, and tools for building software applications. Basically, an API specifies how software components should interact. Additionally, APIs are used when programming graphical user interface (GUI) components."

Put simply, an API declares an interface for you to interact with its logic without you having to know what is happening under the hood, masking the complexity and making it easy to consume and use.

What is an eCommerce API

Ok, so now we’ve defined an API at a high level so let’s get down to what an “eCommerce API” is. An eCommerce API is a collection of eCommerce functionality exposed via API, fairly straight forward. To break down the specific eCommerce functionality this includes at the very minimum, cart, checkout, payments and orders - or in other words a way to transact. One point of confusion that we sometimes here is that a payment gateway is an eCommerce API, when in reality these providers offer a single service, namely a payments API, eCommerce is a broader journey comprised or more steps.

Why use an eCommerce API

So as we just defined above, APIs allow you to interact with the logic without needing to know what is happening under the hood. This is great for eCommerce because there is a ton of logic that you need to access but at the same time you don’t want to have to handle the complexity that supports all of this logic.

An API is the ideal delivery mechanism for eCommerce because eCommerce logic and functionality can be inherently complex.

This creates a natural split between your frontend and backend operations and the underlying commerce engine. This turns ordinary developers into super-charged developers thanks to increased efficiencies and productivity. No longer do you need an expensive full stack or proprietary eCommerce platform developer. This allows you to deploy new commerce solutions and get to market faster whilst enjoying access to a wider developer talent pool.

Evaluating an eCommerce API

Not all eCommerce APIs are created equal.

Below you’ll find some key areas to consider and explore when you come to evaluating an eCommerce API that will fit your business and/or project requirements.


So first up is to know what type of eCommerce API you are evaluating or looking for, the two industry standard options today are REST and GraphQL APIs.

Both have their pros and cons which would make for another post entirely. In short there is no right or wrong answer. Each type of API is useful for different situations and can even be used in parallel.


For a further and more general analysis of the differences between types of APIs including GraphQL and REST we recommend checking out these great resources or googling “API design patterns”:




The Moltin API closely follows the RESTful JSON:API specification which handles and addresses some of the negatives of RESTful APIs to create a well rounded, performant eCommerce API. This does not stop you from leveraging GraphQL by building your own GraphQL layer in front of our API.

Location & response times

Whether this be for legal, security, or compliance reasons the location of the eCommerce API and it’s databases is something else you will likely need to consider.

While edge caching can certainly ensure your content & data is located close to your end customers, the types of data that can be pushed to the edge can be limited for eCommerce use cases and data and only really works for GET requests (retrieving data). When it comes down to commerce logic and interactions (e.g. the critical purchase path through cart and checkout) this can not be cached. If an eCommerce API is located halfway around the world this can impact latency, your applications performance and ultimately the conversion rate of your store.

Milliseconds Matter

You’ll ideally want to ensure the location of your eCommerce API is within or close to the location of your customers and the response rates are below 200-300ms for the most part, although there are some exceptions for more complex queries. 

API-first or API bolt-on

There is another key difference to be aware of when evaluating eCommerce APIs and that is to go back and understand how the API first came to be.

Many traditional eCommerce platforms did not start out with an API and instead built APIs as a bolt on to their core platform, primarily to enable an ecosystem of third party integrations. This key difference affects the feature/functionality coverage area of the API in terms of what is available and also how the API fundamentally works as it has to interact with this more closed, restrictive platform core.

On the other hand API-first means exactly that, the entire product has been designed from the ground up to be consumed via APIs (as Moltin has been). This leads to 100% (or close to) coverage in feature functionality.

We usually find that those that adopt an API-first eCommerce service implement their projects far faster than with a solution that uses bolt-on APIs, as there are less work arounds and hacks required to achieve your desired results.

Feature / functionality

So we mentioned in the definition that a commerce API is comprised of a few core elements, products, carts, checkout, payments and orders. Outside of this core functionality there are multiple other services that you may need to call upon. Sometimes these may exist inside the eCommerce API itself. A drawback here is that this feature/functionality might be tightly woven into the core services meaning you'll be back to hacky work arounds when you’re looking to branch out to other best in class providers or writing your own logic - for example you want to replace the tax functionality inside the eCommerce API with a best in class vendor like TaxJar.

Feature functionality (or the lack of) leads onto the next and arguably one of the most important things to consider when evaluating an eCommerce API.

Interoperability & extensibility

Most eCommerce APIs tend to enable custom data in two different ways. The first is as simple key value pairs which is great if you’re just storing some simple data but can fall short for more complex scenarios as the onus on validation rests entirely with the development The second way that traditional eCommerce platforms handle customization is on a case by case, specific feature/functionality basis. I.e. How you extend the product catalog is completely different to how you extend the customer record or an order. This greatly increases the learning curve of the platform and slows down development time as you find yourself hopping from one dashboard page, directory, file or line of code to the next.

Here at Moltin we understand that commerce data likely needs to be well defined, structured with data types and relatable. It also needs to be universal. One single way to implement and  easy to pick up, learn and implement without a lengthy learning curve.

Beyond extensibility of the schema comes interoperability, or in other words the way in which the API integrates with other providers and vendors. With structured custom data as part of the puzzle you also have to look towards how the events and communication works between other best in class services.

The standard here is webhooks, and just like API-first vs bolt-on APIs, the coverage and types of webhooks available can vary wildly. The other more traditional approach is a rigid plugin driven system design which can again lead to hacky work arounds. Webhooks pair up well with a more open  and modern integration pattern that revolves around serverless functions.

Here at Moltin we have bundled up the concept of structure data, real time events/webhooks and serverless functions into what we call Flows. You can learn more about flows here.

Developer Experience & Documentation Quality

The quality of the developer experience is another important factor to consider as a poor experience can negatively impact your time to market, significantly increase maintenance and ultimately development cost.

A few key considerations you should explore & questions you should ask when it comes to the developer experience include:

Is the eCommerce API consistent, standardized and human read-able to requests and response objects across all endpoints or is each API endpoint different and require it's own learning curve? i.e. Can a developer read the documentation in a couple of minutes for one endpoint and re-use that knowledge across all API endpoints.

Has the eCommerce logic and complexity been well abstracted or are there multiple endpoints and features spread across multiple requests. i.e. it takes several API requests to process an action that could be handled in a single request. Having to make several round trip calls can slow down implementation and your web applications performance.

Are there examples and SDKs in your language available and supporting high quality accurate documentation to help you onboard quickly?

How easy is it to navigate and browse the documentation to find answers to your questions?

Is there a change log and status page? Knowing when something has changed or when services encounter issues is critical to the smooth operation of your business.

Is there a community forum or ticket based support system for questions, best practice advise or for when things go wrong?


As you can see, when it comes to understanding what an eCommerce API is and how to evaluate what makes a great eCommerce API there are many things to consider. This article is in no way an exhaustive list and is simply some of the top areas you should consider when evaluating an eCommerce API.

Hopefully this article gave you some insights into how you should approach and think about eCommerce APIs.

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