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API – Application Programming Interface

An API (Application Programming Interface) is a defined interface through which software systems exchange data and invoke each other's functions. In an ERP context it is how the system connects to storefronts, integration platforms, banking links, carriers, tax engines and in-house applications — and increasingly it is a selection criterion in its own right, because an ERP that cannot be integrated cleanly limits everything you build around it.

What an API actually specifies

An API describes what a system offers without exposing how it works internally. In practice it defines endpoints (addresses that expose specific operations, such as /customers or /orders), methods (read, create, update, delete), a data format (JSON or XML), authentication (API keys, OAuth 2.0, client certificates), and a versioning policy so integrations survive vendor updates.

That last item is the one buyers skip and integrators care about most. An API without a versioning commitment is a moving target, and every vendor release becomes a regression test of your integrations.

The types you will encounter

REST/HTTP is today's default: lightweight, JSON-based, documented through OpenAPI. SOAP is XML-based and more formal, still widespread in older enterprise systems and not a red flag by itself — plenty of stable, well-documented SOAP interfaces are in production. OData adds standardized query capability on top of REST and appears frequently in the Microsoft ecosystem. GraphQL lets the client choose which fields come back, elegant for complex reads and still uncommon in mid-market ERP.

Webhooks are the inverse pattern: instead of you asking, the ERP calls your endpoint when an event occurs. For order integration or inventory sync this is the difference between real time and a five-minute polling delay. EDI and file interfaces — CSV, XML, EDIFACT — are technically not APIs but remain mandatory in supply chains where trading partners set the rules.

API-first, and what it means in practice

An API-first ERP exposes functionality through APIs before building a user interface on top, which means anything a user can do, an integration can do too. The alternative — an API bolted onto a legacy core — typically covers the objects somebody once needed and stops there. You find the gaps during implementation, at the worst possible moment.

The practical test during evaluation: pick a real process you intend to automate and ask the vendor to show the API calls that would implement it. A vendor whose answer requires a services engagement has answered the question.

Related topics

Frequently asked questions

How do I tell a good ERP API from a bad one before buying?

Public documentation is the first filter: if it requires a partner login, assume the API is an afterthought. Then check coverage — can you create and update the objects you need, or only read them? Rate limits, a sandbox environment, and an OpenAPI specification are the marks of an interface someone maintains as a product rather than a feature checkbox.

Are webhooks better than polling?

For anything time-sensitive, yes, because you find out when something happens instead of asking every five minutes. The cost is that you need an endpoint that is always reachable and handles retries and duplicate deliveries correctly. Many teams start with polling because it is simpler to operate, then move to webhooks when the latency becomes a business problem.

What breaks integrations over time?

Version changes and undocumented behavior. A vendor that versions its API and deprecates on a published schedule lets you plan; one that changes response fields in a minor release gives you an outage. Ask about the deprecation policy during selection — the answer tells you what maintaining the integration will cost over five years.

Is EDI still relevant if the ERP has a modern API?

Yes, because the choice is rarely yours. Large trading partners in retail, automotive and healthcare mandate EDI transaction sets, and your API preferences do not enter into it. The practical setup is an API-capable ERP behind an EDI translator or integration platform that speaks both.