Dynamics 365 Extensibility Done Right: Custom APIs vs Custom Actions

Stop Treating Them as the Same Thing

For years, many Microsoft Dynamics 365 developers used Custom Actions as the default way to expose reusable business logic inside Microsoft Dataverse.

And honestly, that made sense at the time.

Actions gave us:

• Input/output parameters
• Reusable server-side operations
• Workflow integration
• A way to centralize business processes beyond plugins

But the platform evolved.

Today, we have Custom APIs — and they are not just “Actions but newer.”

They represent a completely different architectural mindset.

The mistake many teams still make is treating:

• Custom Actions
• Custom APIs

as interchangeable implementation details.

They’re not.

And choosing the wrong one affects:

• Maintainability
• Integration quality
• Security boundaries
• API design
• ALM
• Long-term scalability

This article breaks down:

• What each one really is
• How Microsoft positions them
• Where each shines
• And how to make the right architectural decision

What Exactly Is a Custom Action?

A Custom Action is essentially:

A process-based operation built on top of the old workflow infrastructure.

Under the hood, Actions belong to the same family as:

• Workflows
• Dialogs
• Process entities
• Classic automation components

You define:

• Input parameters
• Output parameters
• Optionally attach plugin logic

Then Dynamics exposes it as an Organization Request message.

Example

var request = new OrganizationRequest("new_ApproveInvoice");
request["InvoiceId"] = invoiceId;

service.Execute(request);

Simple.

Effective.

But also deeply tied to legacy platform concepts.

Why Custom Actions Became Popular

Back in the early Dynamics CRM days, Actions solved several painful problems.

Before Actions:

• Plugins were isolated
• Logic reuse was difficult
• Workflows had limited extensibility

Actions introduced:

• Reusable callable operations
• Parameterized execution
• Workflow invocation
• JavaScript execution
• Web API exposure

For many years, this was the cleanest abstraction available.

And to be fair: they still work perfectly fine today.

Where Custom Actions Start to Break Down

The problem is not functionality.

The problem is architecture.

As systems became:

• More integrated
• API-driven
• Microservice-oriented
• Externally consumed

…the limitations of Actions became obvious.

Problem #1 — They Are Built on Workflow Infrastructure

This is the biggest hidden issue.

Custom Actions are not truly independent API objects.

They rely on:

• Process entities
• Workflow execution internals
• Older metadata concepts

That creates long-term architectural coupling.

You’re effectively building service operations on top of automation infrastructure.

That’s not ideal.

Problem #2 — Weak API Contract Definition

Actions expose parameters.

But they don’t behave like carefully designed service contracts.

There’s limited control over:

• Discoverability
• Metadata clarity
• Validation semantics
• Privilege exposure
• Consumer-facing design

This becomes painful when:

• Frontend teams consume your endpoints
• External systems integrate
• ISVs depend on your API behavior

Problem #3 — ALM and Versioning Challenges

Versioning Actions cleanly is awkward.

Changing:

• Parameter names
• Response structures
• Behavior

…can easily break consumers.

Because Actions were not originally designed as public service endpoints.

Modern APIs require:

• Backward compatibility strategies
• Contract stability
• Semantic evolution
• Explicit ownership

Custom Actions were never optimized for that.

Enter Custom APIs

Custom APIs are Microsoft’s modern answer.

And architecturally, they are a major improvement.

A Custom API is:

A first-class Dataverse operation explicitly designed to behave like a proper service endpoint.

That sounds subtle.

It isn’t.

Why Custom APIs Matter

Custom APIs separate:

• Business operations

from

• Workflow/process infrastructure

That separation is huge.

Instead of “workflow-driven callable logic,” you now get:

• Explicit messages
• Explicit contracts
• Explicit privileges
• Explicit service semantics

This aligns Dynamics 365 with modern enterprise architecture patterns.

The Mental Shift

This is the key mindset change.

Custom Actions

“I need reusable CRM logic.”

Custom APIs

“I am designing a platform service.”

That difference changes how you think about:

• Ownership
• Contracts
• Consumers
• Versioning
• Security
• Long-term evolution

Advantages of Custom APIs

1. Clean API Contracts

Custom APIs give you much more deliberate control over:

• Request parameters
• Response parameters
• Binding
• Visibility
• Discoverability

You define operations intentionally.

That matters enormously for enterprise integrations.

2. Better Security Control

Custom APIs support:

• Privilege binding
• Private APIs
• Role-based exposure
• Explicit execution governance

This is a major upgrade over traditional Actions.

Especially in regulated environments.

3. Better for External Integrations

This is probably the biggest win.

If:

• Another system
• Frontend SPA
• Mobile app
• Azure Function
• Power Platform app
• External partner

…needs to call your logic, Custom APIs are simply the better architectural choice.

They behave predictably.

They feel like real APIs.

Because they are.

4. Better Long-Term Maintainability

Custom APIs encourage:

• Separation of concerns
• Service-oriented thinking
• Cleaner abstractions
• Clearer ownership boundaries

Over time, that dramatically improves maintainability.

Especially in large enterprise environments.

Plugin Integration Is Excellent

One of the strongest aspects of Custom APIs is that they work beautifully with plugins.

The common pattern becomes:

This creates:

• Cleaner layering
• Better testing opportunities
• Reusable services
• More maintainable codebases

Instead of dumping logic directly into plugins.

So Are Custom Actions Obsolete?

No.

Not even close.

This is important.

Custom Actions still make sense in many scenarios.

Especially when:

• The operation is fully internal
• Tightly coupled to CRM automation
• Workflow-triggered
• Rapidly implemented for business processes

They remain:

• Supported
• Stable
• Widely used

The mistake is not using Actions.

The mistake is using them everywhere by default.

My Rule of Thumb

Here’s the framework I personally use.

Use Custom Actions when:

• The operation is internal to Dynamics
• Workflows/processes depend on it
• Business users trigger it
• Speed of implementation matters more than API architecture

Use Custom APIs when:

• External systems consume the operation
• Contract stability matters
• Security boundaries matter
• Versioning matters
• The operation represents a real platform capability

Real-World Examples

Good Custom Action Use Cases

Internal Approval Process

• Submit Expense Report
• Approve Leave Request
• Escalate Case

These are CRM-native operations.

Perfectly fine as Actions.

Good Custom API Use Cases

External Integration Endpoints

• Create Customer From ERP
• Sync Warehouse Inventory
• Calculate Loan Eligibility
• Generate Invoice Preview

These are service operations.

Custom API territory.

Microsoft’s Direction Is Clear

If you look closely at recent Dataverse evolution, Microsoft is clearly investing in:

• API-first architecture
• Dataverse service extensibility
• Modern integration models
• Explicit operation contracts

Custom APIs align directly with that future.

Actions align with legacy process infrastructure.

That doesn’t mean Actions disappear tomorrow.

But it absolutely tells you where the platform is heading.

The Biggest Architectural Lesson

The real lesson here is bigger than Dynamics 365.

It’s this:

Business logic should be designed as services — not accidental side effects of platform automation.

Custom APIs push developers toward that mindset.

And honestly, that’s a very good thing.

Final Thoughts

Custom Actions helped Dynamics developers for years.

They were innovative when introduced.

But modern enterprise systems require:

• Cleaner contracts
• Stronger boundaries
• Predictable APIs
• Better integration architecture

That’s exactly why Custom APIs exist.

So before creating your next Action, ask yourself:

“Am I automating CRM behavior… or designing a platform capability?”

Your answer should determine the implementation.

What’s Your Preference?

Are you still heavily using Custom Actions in production systems?

Or has your team fully shifted toward Custom APIs?

I’d love to hear how other architects are approaching this transition in real enterprise environments.