What is the Dynamics 365 Web API?

The Dynamics 365 Web API is a RESTful OData-based interface used to interact programmatically with Microsoft Dataverse data and functionality, which forms the data platform underneath Dynamics 365 Customer Engagement applications. It enables applications to perform operations such as: Create records Retrieve records Update records Delete records Execute functions Execute actions Query related data Associate/disassociate records The Web API is based on: HTTP + REST + OData + JSON + OAuth authentication Basic architecture A client application might communicate with Dynamics 365 like this: Custom Application ↓ HTTPS ↓ Dynamics 365 / Dataverse Web API ↓ Dataverse ↓ Business Data Authentication is generally handled through Microsoft Entra ID and OAuth-based access tokens. CRUD operations The API supports standard HTTP operations. Create POST Creates a record. Retrieve GET Retrieves data. Update PATCH Updates selected properties. Delete DELETE Deletes a record. This maps naturally to CRUD: POST → Create GET → Read PATCH → Update DELETE → Delete OData querying One of the most powerful aspects of the Dynamics 365 Web API is its OData query support. Common query options include: $select $filter $expand $orderby $top For example, conceptually: /accounts? $select=name,accountnumber &$filter=statecode eq 0 This means the client can request only the required data instead of retrieving entire records. That's important for: Performance Network efficiency API scalability Client-side processing $select Use $select to specify required columns. Instead of: Retrieve everything request: name accountnumber revenue This follows the principle: Retrieve only what you need. $filter Filtering allows server-side filtering. Conceptually: $filter=revenue gt 1000000 Instead of retrieving thousands of records and filtering them in JavaScript, let Dataverse perform the filtering. $expand $expand allows navigation through relationships. For example: Account ↓ Contacts A client can retrieve an account together with related information where appropriate. This is particularly useful when working with Dataverse relationships. Web API vs Organization Service Historically, Dynamics CRM developers frequently worked with the .NET Organization Service / SDK. Modern integrations often use the Web API when they need: REST JavaScript SPA applications Cross-platform integrations HTTP-based integrations Language-independent communication The Web API isn't restricted to C#. A client could be written in: JavaScript C# Python Java Node.js PowerShell provided it can make authenticated HTTP requests. Web API and Dataverse security Calling the Web API does not bypass Dynamics 365 security. The authenticated identity is subject to Dataverse security mechanisms such as: Security roles Business units Privileges Record-level access Field-level security where applicable Teams Ownership/access mechanisms Therefore: Web API ↓ Dataverse security ↓ Authorized data access This is a critical enterprise concept. Web API vs Custom API Another common interview distinction: Web API The HTTP/OData interface exposed by Dataverse. Custom API A Dataverse customization mechanism that allows developers to define custom operations/business capabilities that can be invoked through supported Dataverse interfaces. So a Custom API can effectively expose custom business logic, while the Web API is the broader communication interface. Interview-level answer The Dynamics 365 Web API is a RESTful OData-based interface for interacting with Dataverse and Dynamics 365 Customer Engagement data. It uses HTTP methods such as GET, POST, PATCH, and DELETE, supports OData query options such as $select, $filter, and $expand, and uses Microsoft Entra ID/OAuth-based authentication. It is widely used for JavaScript customizations, integrations, external applications, and cross-platform solutions while still enforcing Dataverse security.