ASP.NET 5 MVC: unable to connect to web server 'IIS Express'

Question

What I'm doing:

• Opening Visual Studio Community 2015
• File -> New -> Project
• Under Visual C#: Web -> ASP.NET Web Application
• Web Application
• And press f5 for the popup error "unable to connect to web server 'IIS Express'."

Deleting applicationhost.config, located in Documents\IISExpress\config, doesn't change the error message. (There's also an IISExpress folder in program files and program files (x86).)

Something I noticed, and I don't know if it's a problem:

Referenced file 'lib/jquery-validation/jquery.validate.js' not found.

I got a dump with rawcap but I don't notice much in there. Some of what was there:

"Framework":{"FrameworkName":"DNXCore,Version=v5.0","FriendlyName":"DNX Core 5.0","ShortName":"dnxcore50","RedistListPath":null}

I don't notice a problem, but I have the network data if that can help figure out why I cannot connect to the web server. I get a RST,ACK immediately so I'm guessing the port is closed and whatever this web server is, isn't being setup.

More on this problem: 800700c1 error from /trace:error

I've tried:

• deleting applicationhost.config (and changing port number)
• running visual studio as administrator
• deleting IISExpress folder in Documents (changes error message until the folder is reinstalled)
• toggling ssl off and on, copying url to launch box. (note: I'm not using ssl)
• clearing all sfc /scannow errors
• starting iisexpress with x86 version and 64-bit version

Solution 1

After installing Update 2 for Visual Studio 2015 I started getting the same error. I tried everything above with no luck. However, I found a solution that works for me:

1. Delete YourSolutionFolder\\.vs\config\applicationhost.config file (note: .vs is a hidden folder)
2. Open Visual Studio, right-click on web site > Properties > Debug tab > Web Server Settings > App URL - change port number.

If you have IIS configured to use the same port, (stop the application / use different port) and try again.

Solution 2

Exit VS and delete the (project)\.vs\applicationhost.config file. Restart VS. It should start working.

Solution 3

Try using a different port. I just set up a new Core 1.0 RC1 project and got the same error.

• Right click web project
• Debug tab
• Toggle Enable SSL off and on again, it should generate a new random port
• Copy the SSL URL and paste into Launch URL box
• Run the project

Worked for me (TM).

Answer from: https://stackoverflow.com/a/28650554/134761

Solution 4

I had this issue on .net core 2.1, visual studio version 15.9.6. When i deleted the .vs folder, i reopened visual studio and the problem was still there. The solution that worked for me below:

1. Delete .vs folder (it is a hidden folder).
2. Restart Computer.

Other Solutions:

• Close Visual Studio, delete bin and obj folders from the project folder. Open Project then rebuild solution.
• Try running Visual Studio as Administrator.
• Clean Solution then rebuild
• 1. Clean Solution. 2) Exit Visual Studio. 3) delete .vs folder 4) Re-open Visual Studio
• Restart machine (if you can afford to)

Solution 5

Copied my comment to an answer by request.

For Net Core 2.2 project - After a MASSIVE struggle and trying everything from deleting .vs folder, deleting IIS Express configs, changing port numbers, changing bindings, and to running VS as admin I FINALLY fixed issue by

1. closing VS,
2. deleting launchSettings.json
3. opening VS which re-generated launchSettings.json.

It was not apparent that the file was corrupt or incorrect or even when it changed to cause failure.

View more solutions

Comments

[mariocatch]

Does this help? stackoverflow.com/questions/15873126/…. Or changing the port? stackoverflow.com/questions/23502327/…

[Hazem Torab]

try when you open visual studio right click and open as administrator..

[Sarek]

I'm trying all suggestions people give me even if I have tried before.

[Sebastian 506563]

can you open new project an check if this is working? Restart PC? Move project to other directory

[Sarek]

Thank you but that also didn't work.

[Andrei]

@Sarek, were you able to find a solution? If so, do you mind answering your own question? We are having the same issue.

[Sarek]

I tried everything and cleared everything up with sfc /scannow. Then I gave up and just did a repair install. That worked, but I have no idea what the problem was.

[nam]

@Sarek In my case just closing and re-opening the VS2015-Update3 worked. I'm using ASP.NET core 1.1. Maybe, with new version, steps I took was good enough to resolve the issue or different users have different solutions depending on their VS configurations etc.

[Lex Li]

ASP.NET Core in Visual Studio 2015 is not considered as a fully supported scenario, so such issues are expected. All users should migrate to Visual Studio 2017, or switch to Visual Studio Code.

[Lamar]

This happens to be every once an a while after changing absolutely nothing. The issue has been around for awhile and MSFT still hasn't worked it out. Hate them for it and their support sucks. Screw them.

[JGilmartin]

this article solved my issue -> overengineer.net/…

[Mahmut EFE]

Close Visual studio. Try to delete Bin, Obj and vs folder. After that problem should resolve, It worked for me.

[VSO]

Last time restarting worked. This time, it didn't. Deleted project, re-pulled. Didn't help. Delete project, re-pulled, restarted. Works. Not sure, but not worth spending more time on.

[René Sackers]

Man, my error came back, found this as well on another site, but it just keeps giving the damned error. Pissing me off. I'd run the web console, but that doesn't have a watcher, so that I can just ctrl + s, refresh.

[René Sackers]

Omg, it works. I deleted the IISExpress folder in my documents, then I deleted that file, then I started getting this error, but the accepted answer was the solution: stackoverflow.com/questions/33166403/… and now it's working :|

[aruno]

I had to do this to increment the port number. my original post was 'stuck' and I don't have time now to reboot or figure out how to fix it

[Michael]

Just installed Update 3, started getting this error after adding a new class to a Core project. This solution worked for me.

[EKanadily]

It worked but only when i used port 60000 . port 6000 returned error : unsafe port.

[Shiham]

May be explain you answer a bit. Just killing the process might not be the answer here. And what after?

[mlienau]

This worked for me in VS2017, without having to change the port.

[wisetap.com]

After doing this for me was needed run Visual Studio as Administrator, and worked, thanks!

[Bart Mensfort]

Especially the RUN AS ADMINISTRATOR is important for me. (although I have Asp.net Core 2.0 VS2017.

[Lex Li]

When launchSettings.json is automatically generated or updated by VS, the applicationUrl should have / in the end. More info can be found in blog.lextudio.com/…

[Lex Li]

Only administrator permissions allow the application to bind to a port number smaller than 1024. That's why 6767 works for you.

[FindOutIslamNow]

Deleted the whole .vs folder and worked for me, just that

[Tonmoy]

Restarting VS2017 didn't fix but restarting the computer fixed it for me. Didn't need to change the port or delete the folder. Hope it helps others.

[Lamar]

Changing the port number is annoying af when you have saved testing requests

[MercifulGiraffe]

This worked for me, but also only after I restarted VS in Administrator mode.

[Muhammad Musavi]

Non of these solutions worked for me, If you have installed default Windows IIS (Which comes with your windows) and have access to it, try to use it, that solved my problem, simply Add new website or new application there and it's done, anyway it's weird that IIS Express is unable to open up the page. If you need to trace it, just attach it to a process using ctrl + alt + p short keys and check Show process for all users and select w3wp.exe (sometimes need to refresh the website to find w3wp.exe) and then hit the Attach button.

[Prolog]

This is not a solution, but a workaround. Your answer suggest using different server - Kestrel - while OP clearly is trying to get IIS-Express to work.

[laggingreflex]

For me it was .vs\config\<MyProject>\config\applicationhost.config

[Meir]

After three days of plucking hair, this solution helped me. Thank you

[GMc]

This is a bit unclear, what do you mean by "just change all port numbers to new of any work8ng series"? Can you provide more detail as to how this answers the OP or which parts of the OP it answers? Do you have a working example you can post?

[CodyBugstein]

where do you see web site that you need to right click on?

[Madhusudhan V Indian]

I mean , change project deployment ports , for example local host:55314 like that ... Generally default is 44304 like , so change that ... Then all starts working.

[Sentinel]

Worked for me, but had to do it twice!

[Robert Bratton]

I was able to do this by shutting down only Visual Studio, deleting the .vs folder, stating Visual Studio again.

[Daniaal]

Yeah it works for some not in my case though. No idea why it didn't work. The only thing that did was restarting my computer.

[Sonali]

It works but no need to restart computer.Only close the Visual Studio. Delete the .vs folder and again start the visual studio. I am using visual studio community 2019

[Daniaal]

Ah ok, glad it worked. Mine was weird cause when i opened the message, it would still not work and after restarted it worked. Must be a lock and configuration gone wrong in a file in the vs folder.

[Dan Orlovsky]

VS 2019 - .vs\config\<MyProject>\config\applicationhost.config worked for me, too.

[Ulysses Alves]

I'm running VS as Admin but I still get the same problem.

[johnbt]

Got this after a bluescreen. Had to delete .vs folder and restart the computer. Restarting visual studio was not enough.

[Daniaal]

Glad it worked for you! Never happened to me since but there may have been a fix. I'm now running the latest version of Visual Studio.

[Daniaal]

@SarahLissachell Amazed me too! Took me hours to figure it out so i am glad it helped :)

[Matt Searles]

Changing the port number did the job for me

[WeisserHund]

This was the solution for me, Thanks

[MedievalCoder]

Although a manual clean often times does help, it won't resolve the issue in this case as the problem resides in the applicationhost.config file and is most likely caused by trying to use the same ip address twice

[EJoshuaS - Stand with Ukraine]

Didn't work in Visual Studio 2019 - it just used the same port each time.

[dxk3355]

Using the same software as you. I've done reboot, deleting vs folder, deleting bin/obj, start as admin, change the ports, reinstall IIS Express, and nothing has fixed this. It seems to kick off a refresh IIS Express instance every time I start the debugger then forgets itself.

[angularsen]

@EJoshuaS-ReinstateMonica I believe this has changed a lot. Take a look at how your Startup class is configured and what appsettings.json files you have. There is also Properties\launchSettings.json to launch different profiles locally. docs.microsoft.com/en-us/aspnet/core/fundamentals/… dejanstojanovic.net/aspnet/2018/december/…

[Quinton Smith]

For Net Core 2.2 project - After a MASSIVE struggle and trying everything from deleting .vs folder, deleting IIS Express configs, changing port numbers, changing bindings, and to running VS as admin I FINALLY fixed issue by 1. closing VS, 2. deleting launchSettings.json 3. opening VS which re-generated launchSettings.json. It was not apparent that the file was corrupt or incorrect or even when it changed to cause failure.

[samneric]

My steps were compressed to: 1) Clean Solution. 2) Exit Visual Studio. 3) delete .vs folder

[Daniaal]

@samneric Thanks for that, i'll add you solution to the answer :)

[samneric]

actually, it worked once then the issue came back lol. My situation ended up being caused by Docker. This ended up being the ultimate solution... stackoverflow.com/a/61579820/558509

[Mitulát báti]

VS shouldn't be run with Admin rights. If you can solve a problem only by starting in Admin mode you're probably doing something wrong.

[krunal.cp]

The solution worked. Thanks :) How about DELETE the .git folder as well?

[Patrick Borkowicz]

Seems to happen randomly for me. Only a reboot fixes it. In the case of ASP.NET Core projects I usually just run the project without IIS Express, which is the green drop down arrow next to the 'play' button in VS, switch to <projectname>. As far as I know this is the same as running dotnet build and dotnet run from the command line.

[yogihosting]

Also .vs folder is a hidden to un-hide it first.

[Anand Murali]

Thank you @QuintonSmith. Your solution worked for me in .NET Core 3.1 as well.

[Alex Pandrea]

to highlight the change: http instead of https

[Alex Pandrea]

I subscribe: after playing with netsh configuration trying to make the server accessible from outside I encountered this problem. Forgot what I did and tried almost all the other answers until deleting the iplisten entry as described here. It seems like IISExpress has no error message in such a case.

[Amir Hajiha]

You are not a start, but a superstar! Thanks it worked

[Sanket Sonavane]

Thanks Quinton you saved the day

[Sk Shahnawaz-ul Haque]

Thanks @QuintonSmith, your solution is working in Visual Studio 2019 Preview for ASP.NET Core 5 (.NET 5 RC2 SDK) as well.

[isierra]

First try I deleted .vs folder and it didn't worked. Second try I deleted the folder and restarted the computer, and it is working perfect! Thanks

[Abdullah Tahan]

keep in mind with will delete all the previous setting like swagger or docker so just make a copy of the old one @QuintonSmith.

[burgoyne]

Worked for me in VS 2019 with a .NET Core 5 project. The file path was slightly different: .vs\<MyProject>\config\applicationhost.config

[havij]

Worked in 2019 as well, without having to change the port.

[Azoreo]

@QuintonSmith Thank you again. Deleting launch settings fixed it for me, whereas the other solutions did not. Whew!

[Scuba Steve]

Lifesaver, worked in vs 2019, with Asp.Net Core 3.1 - the applicationhost.config file is one further directory deep in the .vs folder.

[rory.ap]

@QuintonSmith Can you please make an official answer? I keep having to dig to find this when it happens every few months.

[Quinton Smith]

@rory.ap - As requested - stackoverflow.com/a/65421182/4977243

[Bigyan Devkota]

this worked for me, was an easy solution -- thanks

[exrezzo]

Thank you @QuintonSmith it worked for me on .net core 3.1

[viniciusalvess]

After trying a whole bunch of things. This solved my issue. Thank you @Jason J. Lee

[WSK]

This is work around not a solution. In team development you can't change the debug port at your will.

[sean717]

@QuintonSmith... you, my man...deserve a medal. God bless you.

[Alexander Zaldostanov]

Thanks buddy you helped me alot, I have been trying to fix this stupid error :)

[vandsh]

Anyone using @QuintonSmith's approach of deleting the launchSettings.json it's located under the <project>/Properties folder. Took me a minute to find exactly where it was located but it did the trick!

[Shahid Malik]

Restarting my computer fix the problem.

[John81]

Only other thing that worked for my .NET Core 3 project besides rebooting the computer.

[user2966445]

Still didn't work for me in July, 2021 with VS 2019.

[Poat]

I did all the complicated answers (and some worked) but just restarting the computer did the trick :)

[Faizan Mubasher]

None of this is working for me. VS2019 .NET Core 5.0

[mgPePe]

Worked for me, given I didn't really do any changes before that

[Reven]

Doesn't work for me.

[Talon]

Nope, still get the same error

[StarLord]

@Talon Sometimes there will be more than one instance of the worker process in task manager. Make sure to end all of them.

[user2211290]

It worked for me, someone please elaborate reason for this error

[pradeepradyumna]

This worked for me. Thanks ton!

[Chris W]

Try restarting the computer, as a last resort. If Quinton's workaround does not help.

[Simon C]

In my case it was OneDrive. Restarting that made it change ports and then I was able to run my application.

[obaylis]

Similarly for me, after trying all of the other steps (port, del .vs folder, reboots) I deleted launchSettings and back working. Strange thing is, just deleting .vs folder has worked when I encountered this previously. Not this time.

[Arun]

It is helpful for me.

[mfreedm52]

agreed. tried everything before restart. but restart is the only thing that worked.