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summary: Connect apps covers building integrations with Business Central through REST APIs and OData. It answers questions about creating custom API pages and queries, authenticating (Microsoft Entra ID, basic auth, service-to-service OAuth 2.0), filtering, and request tips such as batching and localization.
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---

# Connect apps

> Connect apps covers building integrations with Business Central through REST APIs and OData. It answers questions about creating custom API pages and queries, authenticating (Microsoft Entra ID, basic auth, service-to-service OAuth 2.0), filtering, and request tips such as batching and localization.

Path: [Integration](../integration.md) > Connect apps · tier official · system integration · narrative reviewed (checked by Opus)

## Overview

This section is for developers who connect external services to Business Central using REST web services. It starts with an overview of the two ways to build APIs: API pages for read-write access and API queries for read-only access. A walkthrough then shows how to write a custom API page in AL.

The getting-started page covers authentication setup and trying calls with the Insomnia REST client. The service-to-service page covers unattended integrations with OAuth 2.0 client credentials. Two further pages cover day-to-day use: filtering OData calls and tips on headers and batch requests.

Start with the API developer overview, then the getting-started page to set up authentication and make a first call. Use the custom API page when the standard APIs do not expose the data you need.

## Key points

- API pages support read-write operations. API queries are read-only and can span multiple tables. Webhooks are supported.
- Custom API pages in AL need APIVersion, APIPublisher and APIGroup. They also use properties such as ODataKeyFields, SystemId, EntityName, EntityCaption and EntitySetCaption.
- Relationships are modeled with parts and navigation properties. The deprecated ODataEDMType complex types should be replaced.
- Getting started covers Microsoft Entra ID (OAuth 2.0) and basic authentication with a web service access key, and testing with Insomnia.
- Service-to-service authentication uses the OAuth 2.0 client credentials flow, with a Microsoft Entra registration and the API.ReadWrite.All and Automation.ReadWrite.All permissions.
- Tips cover the Accept-Language header, OData $batch requests, transactional batches with Isolation: snapshot, and the Data-Access-Intent header with ReadOnly.
- Filtering follows Microsoft REST API guidelines for property-based and range-based filter expressions in OData queries.

## Learn pages

- [API developer overview](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-api): Use APIs to expose information from the database into versioned, OData v4 enabled REST web services.
- [Developing a custom API](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-develop-custom-api): Learn how to develop a custom API page by using an AL extension and accessing it to retrieve responses and make updates through the API.
- [Get started developing Connect apps for Dynamics 365 Business Central](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-develop-connect-apps): Learn how to develop a Connect app for Business Central, including setting up Microsoft Entra authentication and exploring REST APIs with Insomnia.
- [Tips for working with the APIs](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-connect-apps-tips): Provides some tips about working with Business Central API.
- [Using filters with API/OData calls](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/developer/devenv-connect-apps-filtering): Learn how to use filters with API calls to get targeted information in return.
- [Using Service to Service Authentication](https://learn.microsoft.com/dynamics365/business-central/dev-itpro/administration/automation-apis-using-s2s-authentication): Service-to-service authentication enables external services to connect as an application, without impersonating normal users.

Source: Microsoft Learn (CC BY 4.0). Descriptions are Learn's own.