Minimal API is taking too long

Question

Minimal API is taking too long

Falanga, Rod, DOH 900

We're getting close to the end of rewriting a legacy ASP.NET WebForms app using Blazor and Minimal APIs. Both are written using .NET 9. A coworker builds and puts both the Blazor app and Minimal API into their respective websites. According to him, it takes ~4 seconds for any minimal API endpoint to respond. I'll have to do some of my own testing, to verify that. Nevertheless, if this holds true, then we'll have some unhappy users.

So, what do you suggest we do to speed up the API's response time?

AgaveJoe 31,181 Reputation points

2026-02-24T10:51:44.4366667+00:00

To provide an accurate diagnosis, we need more data regarding where the latency is occurring. A 4-second response time can be caused by several factors.

First, please verify if this is a 'cold start' issue. If the first request is slow but subsequent requests are fast, it is likely an IIS/App Service idle timeout issue.

To isolate the cause, I recommend creating a simple 'Hello World' GET endpoint. Use your browser’s Developer Tools (Network tab) to clock the response:

If the simple endpoint is fast: The bottleneck is likely in your business logic or a slow-running database query.

If the simple endpoint is also slow (4s): You may be looking at a network configuration issue or overhead from Windows Authentication.

Please test a minimal endpoint and let us know the results so we can help further.
Falanga, Rod, DOH 900 Reputation points

2026-02-24T14:48:56.6766667+00:00

I did try to clock the response using the browser's Developer tools, but it didn't really give me much to go on. I don't know why, unless it is because I was running the API on my machine and so networking wasn't involved.

Another thing which I'm beginning to think has a lot to do with it is I can only test it with Bruno. My CISO blocks Postman and if I try to install Postman he's got an application that will immediately uninstall it. I bring up Bruno to say that I was experiencing similar slowdowns. However, a colleague of mind, who isn't an employee, but is a contractor, works off-site. And in his home environment he can use Postman. He reports that speeds are much better and more acceptable. So, it may be the tool, more than the API, which is at the root of the problem. And unfortunately, I cannot run Postman to verify that for myself.
AgaveJoe 31,181 Reputation points

2026-02-25T19:16:42.2733333+00:00

Rod, the reason for the 'Hello World' test is to validate the claim that any minimal API endpoint takes 4 seconds. By testing a bare-bones endpoint, you can rule out the tool (Bruno) and the network.

Since 4 seconds is a significant delay, you can even test this without a formal clock—if you load a 'Hello World' GET URL in a browser and it isn't near-instant with a warm application, there is a systemic problem. If it is instant, then the 4-second delay your colleague is seeing isn't a limitation of Minimal APIs, but rather something specific to that endpoint's logic or the tool being used.

3 answers

Your answer

AgaveJoe 31,181 Reputation points

2026-02-24T10:51:44.4366667+00:00

To provide an accurate diagnosis, we need more data regarding where the latency is occurring. A 4-second response time can be caused by several factors.

First, please verify if this is a 'cold start' issue. If the first request is slow but subsequent requests are fast, it is likely an IIS/App Service idle timeout issue.

To isolate the cause, I recommend creating a simple 'Hello World' GET endpoint. Use your browser’s Developer Tools (Network tab) to clock the response:

If the simple endpoint is fast: The bottleneck is likely in your business logic or a slow-running database query.

If the simple endpoint is also slow (4s): You may be looking at a network configuration issue or overhead from Windows Authentication.

Please test a minimal endpoint and let us know the results so we can help further.
Falanga, Rod, DOH 900 Reputation points

2026-02-24T14:48:56.6766667+00:00

I did try to clock the response using the browser's Developer tools, but it didn't really give me much to go on. I don't know why, unless it is because I was running the API on my machine and so networking wasn't involved.

Another thing which I'm beginning to think has a lot to do with it is I can only test it with Bruno. My CISO blocks Postman and if I try to install Postman he's got an application that will immediately uninstall it. I bring up Bruno to say that I was experiencing similar slowdowns. However, a colleague of mind, who isn't an employee, but is a contractor, works off-site. And in his home environment he can use Postman. He reports that speeds are much better and more acceptable. So, it may be the tool, more than the API, which is at the root of the problem. And unfortunately, I cannot run Postman to verify that for myself.
AgaveJoe 31,181 Reputation points

2026-02-25T19:16:42.2733333+00:00

Rod, the reason for the 'Hello World' test is to validate the claim that any minimal API endpoint takes 4 seconds. By testing a bare-bones endpoint, you can rule out the tool (Bruno) and the network.

Since 4 seconds is a significant delay, you can even test this without a formal clock—if you load a 'Hello World' GET URL in a browser and it isn't near-instant with a warm application, there is a systemic problem. If it is instant, then the 4-second delay your colleague is seeing isn't a limitation of Minimal APIs, but rather something specific to that endpoint's logic or the tool being used.

Answer 1

Bruce (SqlWork.com) 83,581 Volunteer Moderator

If they all have. 4 second overhead, it must likely you webapi is timing out connecting to the Kerberos server. And falling back to windows Ntlm. Have your network people do a trace.

Answer 2

Hi @Falanga, Rod, DOH ,

Thanks for reaching out.

A few things you can try to speed it up:

Warm up the API: Keep the app loaded in memory so it doesn’t have to “wake up” every time. That first request can feel slow if the app hasn’t been used in a while.
Optimize per-request work: If your API opens database connections, loads big files, or does heavy calculations on every call, try to reduce that. Do the heavy lifting once if you can, then reuse it.
Check the hosting environment: Make sure the server has enough resources, and the app is set up for responsiveness. Even tiny misconfigurations can add a second or two.
Measure where the slowdown really is: Sometimes the API itself is fast, but a database call or file operation is the culprit. Logging and performance tools can help pinpoint it.

Hope this helps! If my answer was helpful - kindly follow the instructions here so others with the same problem can benefit as well.

Michael Le (WICLOUD CORPORATION) 11,080 Reputation points Microsoft External Staff Moderator

2026-03-03T09:04:27.1633333+00:00

Hello @Falanga, Rod, DOH ,

It's been a while since we last heard from you. Hope things are going well.

If you're still interested or have any questions, feel free to reach out whenever it works best for you.

Answer 3

To improve the response time of your Minimal API endpoints, consider the following strategies:

Optimize Code: Review the implementation of your API endpoints to ensure they are efficient. Look for any unnecessary computations or blocking calls that could be slowing down the response time.
Asynchronous Programming: Utilize asynchronous programming patterns to avoid blocking threads while waiting for I/O operations, such as database calls or external API requests. This can significantly improve performance under load.
Caching: Implement caching strategies for frequently accessed data. This can reduce the need to recompute or fetch data from a database for every request, thus speeding up response times.
Load Testing: Use tools like Bombardier to simulate load and identify bottlenecks in your API. This will help you understand how your API performs under stress and where optimizations are needed.
ThreadPool Management: Ensure that your application is not experiencing ThreadPool starvation, which can lead to slow performance. Monitor the ThreadPool usage and adjust your application’s threading model if necessary.
Profiling and Diagnostics: Use profiling tools to analyze the performance of your API. This can help identify slow parts of your code and provide insights into where optimizations can be made.
Minimal APIs Benefits: Remember that Minimal APIs are designed for better performance with reduced overhead compared to traditional controller-based APIs. Ensure you are leveraging their advantages effectively.

By implementing these strategies, you should be able to reduce the response time of your Minimal API endpoints and enhance the overall user experience.

References:

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Minimal API is taking too long

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