An application interface is a defined way for software applications to communicate by exchanging data or triggering actions through agreed rules and formats. In business systems it is usually built as an API (application programming interface). In the seven days to 8 October 2026, Cloudflare Radar recorded API calls as 59.8% of the dynamic web requests it measured in Australia.
Table of Contents
What is an application interface?
An application interface is a defined method that allows one software application to request data or trigger actions in another application using agreed rules, formats and permissions. This kind of interface is built for other software to use.
It exists so systems can work together without anyone copying data between them. It sets what information can be exchanged, how that information must be structured and who is allowed to ask for it.
In everyday use, “app interface” usually means the user interface instead. MDN Web Docs’ definition of a user interface covers anything that helps a person interact with a machine, from a keyboard or screen to a webpage or the front end of an application.
How does an application interface work?
An application interface works as an agreed boundary between two systems. One application sends a request through the interface and the receiving application responds in a defined and predictable format. As long as the interface stays the same, the vendor behind either system can update its own code without breaking the connection.
Here is what happens when a CRM asks an accounting system for the week’s paid invoices:
- The CRM, or the integration acting for it, sends a request to the accounting system’s interface, naming the data it wants.
- The interface checks which system is asking and whether it is allowed access to that data.
- The accounting system finds the invoices and the interface returns them in the agreed format.
- The CRM, or the integration acting for it, reads the response and updates the CRM’s records.
What does API mean in software?
API stands for application programming interface. It is the most common way software offers an application interface to other systems. A well-designed API exposes only what a given interaction needs and keeps other internal details hidden.
The Australian Government Architecture definition of an API describes it as an intermediary layer that lets data move between different systems, services and libraries. From a business perspective, APIs act as contracts between systems.
Having an API does not connect two systems on its own. Something still has to call the API and map the data from one system to the other. Our guide to how API connectors work covers that layer.
Application interface vs user interface
An app interface and a user interface are often the same thing in everyday speech: the screens and controls a person works with. In business systems the terms split. A user interface is built for people. An application interface is built for other software. Most business platforms offer both, one for staff and one for the systems connected to them.
The table below sets the two side by side.
| Feature | Application interface | User interface |
|---|---|---|
| Primary purpose | System-to-system communication | Human interaction |
| Typical form | APIs and webhooks | Screens, forms and buttons |
| Who uses it | Other software | People |
| Built for automation | Yes | Not by design |
| How changes are handled | Usually versioned, with notice before breaking changes | Redesigned as needs change |
| Example | A CRM sending new customers to accounting software | A sales rep entering a customer on screen |
Types of application interface
Application interfaces are usually grouped by who is allowed to use them. The Australian Government Architecture and IBM’s API explainer both use three levels: private, partner and public. A fourth kind, the event-driven interface, is defined by how it sends data.
Internal application interfaces
Internal interfaces are private APIs, available only within one organisation. They connect an organisation’s own systems, such as an in-house app or an operations database.
Partner application interfaces
Partner interfaces sit between public and private ones: they may be reached over the internet, but only authorised business partners get access.
Public and third-party application interfaces
Public APIs are open to any developer or organisation, generally with few restrictions beyond an API key. The APIs that vendors of accounting, payments or marketing software offer their customers are third-party APIs. A connecting app reaches a customer’s data through them only with that customer’s permission, usually given through an API key or an administrator’s sign-in on the customer’s account.
Event-driven application interfaces
Webhooks are one kind of event-driven interface: the sending system pushes a notification to the receiving one when a specified event occurs.
Application interface examples in business systems
An example of an application interface is the API an accounting system offers so a CRM can send it new customers and invoices. The same pattern often appears where one business system reads from or writes to another.
- A business app shows live records from another system through that system’s API.
- A reporting tool such as Power BI refreshes its data from another system through a connector or that system’s API.
OfficePro Consulting builds the app side of this work through Power Apps development and the reporting side through Power BI reporting. Our business systems integration guide covers how to plan connections like these across a whole business.
What makes a good application interface?
A good application interface is clear about what it offers and predictable in how it behaves. Six traits mark a good interface. Each is cheaper to settle before other systems connect than after several depend on it.
- It has a clear purpose and a defined scope of data and actions.
- It uses consistent names and response formats.
- It checks which system is calling (authentication) and what that system is allowed to do (authorisation).
- It returns errors that say what went wrong.
- It manages versions and gives notice before a change that would break existing connections.
- It is documented clearly enough for a developer to use it.
How do you check whether a system has an API?
Check the vendor’s developer documentation before you buy. A system with an API usually publishes it, along with the data it covers, how to get access and any limits on use. A system without a usable API is usually harder to connect later.
Five questions cover most of what a business needs to know:
- Does the vendor publish API or developer documentation on its website?
- Which records can the API read and which can it create or change?
- What does access need, such as a particular plan, an API key or an administrator’s sign-in?
- Are there limits or extra costs, such as a cap on calls or a fee charged to the app that connects?
- Does the system send webhooks when the records you need change, or does the connection have to keep checking for changes?
Questions 3 and 4 often decide the cost. Some vendors keep API access for their higher plans. Others charge the app that connects. If the answers are unclear, ask the vendor for a trial or sandbox account on the plan you would buy and test a connection before you commit.
The usual routes for a system with no API are file exports, direct database access, screen-based workarounds or people retyping data. Our API integration services start by checking which interfaces your systems offer.
Frequently asked questions
Is an app interface the same as a user interface?
Often it is. In everyday use “app interface” usually means the user interface, the screens and controls a person uses. In business systems “application interface” more often means the API that lets other software use the application. A platform such as a CRM has both.
Can you give an example of an application interface?
An accounting system’s API is a common example. A CRM, or an integration acting for it, uses that API to send new customers and invoices across. Other examples include a reporting tool reading data through an API and a webhook that notifies another system when an order is paid.
What are the two main types of interface in software?
The two main types are the user interface and the application interface. People use the user interface through screens and keyboards. Other software uses the application interface, usually an API, to request data or trigger actions.
Is an API the same as an application interface?
They are close but not the same. An application interface is the general idea of a defined way for one application to use another. An API is the most common way to build one. In business systems the two terms are often used to mean the same thing.
Why does it matter whether software has an API?
An API is the usual way a system shares data with your other systems without someone retyping it. Before buying software, ask whether it has a documented API, what data that API exposes and what it costs to use. A system without one usually ends up connected by exports, database links or manual work.
Next steps
If you are planning to connect systems or want to know whether the software you use can be connected, start with a free initial conversation. OfficePro Consulting will review the interfaces your systems offer and recommend the simplest way to link them.
