What are Custom APIs in Dynamics 365 CE?

Custom APIs in Microsoft Dynamics 365 Customer Engagement (CE) / Dataverse provide a way to define custom operations that can be invoked through Dataverse APIs and business logic.

They are particularly useful when you want to expose business-specific operations rather than forcing consumers to understand the internal implementation of multiple Dataverse operations.

Think of a Custom API as creating your own business operation such as:

Approve Order
Calculate Credit Limit
Submit Application
Generate Invoice
Recalculate Opportunity

Instead of exposing several low-level CRUD operations, you can expose a meaningful business operation.

Why Use Custom APIs?

Consider an order approval process.

Without a Custom API, a client might need to:

1. Retrieve an order.
2. Validate its status.
3. Check approval rules.
4. Update approval information.
5. Trigger additional processing.
6. Return the result.

That logic can become duplicated across Power Apps, JavaScript, integrations, Power Automate, and external applications.

A Custom API can provide a single operation:

ApproveOrder(OrderId)

The server-side implementation can then enforce the business rules centrally.

Custom API Architecture

A Custom API generally consists of:

• API definition
• Request parameters
• Response properties
• Execute privilege
• Optional plug-in implementation
• Binding to an entity or unbound execution
• Dataverse security considerations

The implementation can use a plug-in to execute the business logic.

Conceptually:

Client
   ↓
Custom API
   ↓
Validation
   ↓
Business Logic / Plug-in
   ↓
Dataverse
   ↓
Response

Bound vs Unbound APIs

A bound Custom API is associated with a specific table/entity.

For example:

account → CalculateCustomerRisk

An unbound Custom API isn't associated with one particular record and is appropriate for broader operations.

For example:

CalculateExchangeRate

Why Custom APIs Matter in Enterprise Development

Custom APIs help create a cleaner business-oriented service boundary.

Instead of exposing implementation details, you expose a meaningful operation.

This is particularly useful when the same business capability needs to be consumed by:

• Model-driven apps
• Power Automate
• JavaScript
• Plug-ins
• External integrations
• Custom applications

Custom API vs Custom Action

This is an important interview and architecture topic.

Custom Actions are an older mechanism for creating custom operations in Dataverse. Custom APIs were introduced as a more developer-oriented and flexible approach for defining operations.

For new development, developers should evaluate Custom APIs first, particularly when building developer-focused reusable operations and APIs.

Best Practice

Don't create a Custom API for every simple database operation.

Use one when you have a meaningful business operation or reusable server-side capability.

For example:

CreateCustomer

may simply duplicate standard Dataverse functionality.

But:

ValidateAndApproveCustomer

could represent meaningful business logic.

Interview Takeaway

A strong answer is:

A Dataverse Custom API allows developers to define reusable, business-oriented operations that can be invoked through the Dataverse platform, often with plug-in logic behind them. They are useful for encapsulating business rules and exposing a consistent server-side contract to multiple consumers.