ASP.NET MVC4 Bundling with Twitter Bootstrap

I’m trying to use the new bundling feature in MVC 4 with Twitter bootstrap and it seems to me like the paths to the glyphicons png-files int the css get’s messed up in some way. Heres my code:

 bundles.Add(new StyleBundle("~/bundles/publiccss").Include(

        bundles.Add(new ScriptBundle("~/bundles/publicjs").Include(

I’m not seeing any icons on buttons and likewise. Am I doing something wrong here? Any suggestions?


Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

The issue is most likely that the icons/images in the css files are using relative paths, so if your bundle doesn’t live in the same app relative path as your unbundled css files, they become broken links.

We have rebasing urls in css on our todo list, but for now, the easist thing to do is to have your bundle path look like the css directory so the relative urls just work, i.e:

new StyleBundle("~/Static/Css/bootstrap/bundle")

Update: We have added support for this in the 1.1beta1 release, so to automatically rewrite the image urls, you can add a new ItemTransform which does this rebasing automatically.
bundles.Add(new StyleBundle("~/bundles/publiccss").Include(
            "~/Static/Css/bootstrap/docs.css", new CssRewriteUrlTransform()));

Method 2

The ‘CssRewriteUrlTransform’ works just fine for applications that DON’T run on top of a virtual directory.

So, if your app runs on it runs just fine, but if it runs on you’ll have 404 for all your images because the default ‘CssFixRewriteUrlTransform’ is referencing your images with a ‘/’.

To solve this issue, I have implemented my own version of ‘CssRewriteUrlTransform’ like this:

    public class CssFixRewriteUrlTransform : IItemTransform {
    private static string ConvertUrlsToAbsolute(string baseUrl, string content) {
        if (string.IsNullOrWhiteSpace(content)) {
            return content;
        var regex = new Regex("url\(['"]?(?<url>[^)]+?)['"]?\)");
        return regex.Replace(content, match => string.Concat("url(", RebaseUrlToAbsolute(baseUrl, match.Groups["url"].Value), ")"));

    public string Process(string includedVirtualPath, string input) {
        if (includedVirtualPath == null) {
            throw new ArgumentNullException("includedVirtualPath");
        var directory = VirtualPathUtility.GetDirectory(includedVirtualPath);
        return ConvertUrlsToAbsolute(directory, input);

    private static string RebaseUrlToAbsolute(string baseUrl, string url) {
        if (string.IsNullOrWhiteSpace(url) || string.IsNullOrWhiteSpace(baseUrl) || url.StartsWith("/", StringComparison.OrdinalIgnoreCase)) {
            return url;
        if (!baseUrl.EndsWith("/", StringComparison.OrdinalIgnoreCase)) {
            baseUrl = string.Concat(baseUrl, "/");
        return VirtualPathUtility.ToAbsolute(string.Concat(baseUrl, url));

UPDATE: thanks to superjos who pointed out that there was another solution out there:

public class CssRewriteUrlTransformWrapper : IItemTransform
    public string Process(string includedVirtualPath, string input)
        return new CssRewriteUrlTransform().Process("~" + VirtualPathUtility.ToAbsolute(includedVirtualPath), input);           

Method 3

What you can do is you can go to the customize page and change @iconSpritePath and @iconWhiteSpritePath in the Sprites section and, of course, download the new style.

I’ve put my images in the folder Content/Images folder and I’ve changed the path in:

  • /Content/Images/glyphicons-halflings.png
  • /Content/Images/glyphicons-halflings-white.png

Another alternative is to download all the LESS files from github, change the same variables in the variables.less file and recompile the bootrap.less file with a tool like SimpLESS.

Method 4

Fix for this now added to my AspNetBundling NuGet package which resolves a bunch of other issues in the standard transformer, particularly around using data-uris. Open-sourced on GitHub too.

Just do:

  1. Install-Package AspNetBundling
  2. Replace CssRewriteUrlTransform with CssRewriteUrlTransformFixed

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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