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How to Fix CORS Errors in Word Add-In API Requests

Algirdas Jasaitis Oct 10, 2026 870 views

Question details

The user needs to resolve an Access Denied or CORS error triggered when a Word add-in sends an API request.

How to Fix CORS Errors in Word Add-In API Requests

Product: Microsoft Word Add-in
Device & OS: not provided
Scenario: Developing a Word add-in using C# and JavaScript and attempting to send a JSON POST request to an internal HTTPS API.
Observed behavior: The API request fails and returns an Access Denied or CORS error, preventing the add-in from communicating with the server.

Before you start

Ensure you have access to the backend code or configuration of your internal HTTPS API, as CORS policies must be explicitly defined and allowed by the receiving server.

Solution 1Recommended

Post the Issue in Microsoft Q&A for Specialized Support

Because this issue involves custom API access from a developmental Word add-in rather than a standard Word application feature, escalating to developer forums is the most effective approach.

Microsoft Word add-ins run within a browser control (such as Edge WebView2) which strictly enforces security protocols like CORS. Solving complex cross-origin issues often requires reviewing both the add-in manifest and backend server headers.

Navigate to Microsoft Q&A

Open your web browser and visit the official Microsoft Q&A platform tailored for developer support.

Select the Right Tag

Search for and select the 'Word Management' or 'Office Development' tags to ensure your question reaches experts familiar with the Office JavaScript API.

Include Necessary Debugging Details

Draft your question and paste your exact JavaScript/C# request code, the full API response, your current backend CORS headers, your authentication method, and your add-in manifest details.

Post the Issue in Microsoft Q&A for Specialized Support

Information: Providing complete HTTP header logs (which can be captured using tools like Fiddler or the browser's developer console) will significantly speed up troubleshooting by the support community.

Solution 2

Verify and Update Server-Side CORS Configuration

Fix the error at the source by ensuring your internal HTTPS API explicitly allows incoming cross-origin requests from the Word add-in's domain.

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Frequently Asked Questions

What causes a CORS error in an Office add-in?

A CORS (Cross-Origin Resource Sharing) error occurs because the browser control running your add-in prevents web scripts from requesting resources from a different domain, unless the server explicitly permits it by sending the correct 'Access-Control-Allow-Origin' header.

Why does my API work in Postman but fail in my Word add-in?

Tools like Postman are designed for API testing and do not enforce CORS policies. However, Office add-ins run within a web browser control (like Edge WebView2 or Safari) which strictly enforces CORS for security reasons.

Where can I find the Word add-in manifest details?

The add-in manifest is an XML or JSON file located in the root directory of your add-in development project. It defines your add-in's settings, permissions, and the authorized endpoint URLs that it is allowed to communicate with.

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