When using Twitter Bootstrap LESS with IIS, don’t forget to create the MIME Type [Field Notes]

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I am using the Twitter Bootstrap LESS source with LessJS in an ASP.NET MVC3 Project that deploys to IIS.

  • When I run my local source, the web site displays fine.
  • When I run my build process, it completes fine.
  • When I open the site on my development or production boxes, the CSS doesn’t display.


After making the problem much more complicated than it had to be, I realized that my LESS file wasn’t being found by IIS – not because it wasn’t there or wasn’t being deployed, but because I had never configured IIS to serve LESS files. Rookie move.

To ensure IIS can serve LESS files, take the following steps:

  • Open the IIS 7 Manager application
  • Navigate to your server.
  • From the different options displayed, select MIME Types.
  • On the right-hand side, from the Actions menu, select Add...
  • In the File name extension field, enter .less
  • In the MIME type field, enter text/css
  • Click OK to add the MIME type.

Bingo! Now your server won’t choke when trying to serve a .less file.


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