Software⏱️ 2 min read📅 2026-05-31

How to Fix: Swagger not loading - Failed to load API definition: Fetch error undefined

Learn how to fix: Swagger not loading - Failed to load API definition: Fetch error undefined.

Quick Answer: Try checking your system settings or restarting.

The error 'Fetch error undefined ./swagger/v1/swagger.json' indicates that Swagger is unable to fetch the API definition from the specified location. This issue may arise due to various reasons such as incorrect configuration, missing dependencies, or issues with the ASP.NET Core project.

🔍 Why This Happens

  • [Cause]

🔧 Proven Troubleshooting Steps

Method 1: Configuration Check

  1. Step 1: Ensure that the Swagger configuration is correctly set up in the Startup.cs file.

Method 2: Dependency Inspection

  1. Step 1: Use the `dependencyInjection` method to inspect the Swagger service and its dependencies.

Method 3: API Registration

  1. Step 1: Register the Swagger service in the `Startup.cs` file and ensure that it is properly configured.

✨ Wrapping Up

To resolve this issue, follow the steps outlined above and verify that all dependencies are correctly installed and configured. If the problem persists, consider seeking further assistance from Microsoft support or online forums.

Did this fix your problem?

If not, try searching for specific error codes.

🔍 Search Error Database

❓ Frequently Asked Questions