Microsoft Graph vs Custom API for Office Add-ins
When to use Microsoft Graph, when to build a custom backend API, and how both can work together in secure Office add-ins.
The short answer
Use Microsoft Graph when the add-in needs Microsoft 365 data such as mail, calendar, users, files, Teams, or SharePoint. Use a custom API when the workflow needs private business logic, database access, external systems, or controlled server-side processing.
Many enterprise add-ins use both: Graph for Microsoft 365 context and a backend API for validation, logging, integrations, AI calls, and secure business workflows.
When Microsoft Graph is the right fit
Graph is best when the add-in needs permission-based access to Microsoft 365 resources.
- Read mailbox, calendar, user, file, or SharePoint context.
- Work with Microsoft identity and tenant-level consent.
- Connect Outlook workflows with Teams, OneDrive, or SharePoint.
When a custom API is better
A backend API is useful when the add-in needs logic that should not live in the browser.
- Validate data before writing to CRM, ERP, or databases.
- Hide secrets, API keys, and integration credentials from the add-in client.
- Run AI, background jobs, retries, audit logs, and complex business rules.
References
Common questions
- What is an Office 365 add-in?
- An Office 365 add-in is a web application that runs inside Excel, Outlook, Word, or PowerPoint using Office.js, so teams automate work without leaving Microsoft 365.
- How long does a custom Office add-in project take?
- Discovery is typically 1–2 weeks. A focused Build for one Office app is often 6–12 weeks depending on integrations, Microsoft Graph scope, and security review cycles.
Written by NexaAI Solutions
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