Declaring assets to be processed by Trunk is simple and extensible. All assets to be processed by Trunk must follow these three rules:

This will typically look like: <link data-trunk rel="{type}" href="{path}" ..other options here.. />. Each asset type described below specifies the required and optional attributes for its asset type. All <link data-trunk .../> HTML elements will be replaced with the output HTML of the associated pipeline.

Asset Types


rel="rust": Trunk will compile the specified Cargo project as WASM and load it. This is optional. If not specified, Trunk will look for a Cargo.toml in the parent directory of the source HTML file.


rel="sass" or rel="scss": Trunk uses the official dart-sass for compilation. Just link to your sass files from your source HTML, and Trunk will handle the rest. This content is hashed for cache control. The href attribute must be included in the link pointing to the sass/scss file to be processed.


rel="css": Trunk will copy linked css files found in the source HTML without content modification. This content is hashed for cache control. The href attribute must be included in the link pointing to the css file to be processed.


rel="icon": Trunk will copy the icon image specified in the href attribute to the dist dir. This content is hashed for cache control.


rel="inline": Trunk will inline the content of the file specified in the href attribute into index.html. This content is copied exactly, no hashing is performed.


rel="copy-file": Trunk will copy the file specified in the href attribute to the dist dir. This content is copied exactly, no hashing is performed.


rel="copy-dir": Trunk will recursively copy the directory specified in the href attribute to the dist dir. This content is copied exactly, no hashing is performed.

Trunk is still a young project, and new asset types will be added as we move forward. Keep an eye on trunk#3 for more information on planned asset types, implementation status, and please contribute to the discussion if you think something is missing.

JS Snippets

JS snippets generated from the wasm-bindgen JS snippets feature are automatically copied to the dist dir, hashed and ready to rock. No additional setup is required. Just use the feature in your application, and Trunk will take care of the rest.

Images & Other Resources

Images and other resource types can be copied into the dist dir by adding a link like this to your source HTML: <link data-trunk rel="copy-file" href="path/to/image"/>. Any normal file type is supported. This will cause Trunk to find the target resource, and copy it to the dist dir unmodified. No hashing will be applied. The link itself will be removed from the HTML. To copy an entire directory of assets/images, you can use the following HTML: <link data-trunk rel="copy-dir" href="path/to/images-dir"/>.

This will allow your WASM application to reference images directly from the dist dir, and Trunk will ensure that the images are available in the dist dir to be served.

NOTE: as Trunk continues to mature, we will find better ways to include images and other resources. Hashing content for cache control is great, we just need to find a nice pattern to work with images referenced in Rust components. Please contribute to the discussion over in trunk#9! See you there.


You can instruct Trunk to write the URL passed to --public-url to the HTML output by adding this to your <head>: <base data-trunk-public-url/>.

Trunk will set the href attribute of the element to the public URL. This changes the behavior of relative URLs to be relative to the public URL instead of the current location.

You can also access this value at runtime using document.baseURI which is useful for apps that need to know the base URL on which they're hosted (e.g. for routing).


If you find that you need Trunk to perform an additional build action that isn't supported directly, then Trunk's flexible hooks system can be used to launch external processes at various stages in the pipeline. Hooks can be declared exclusively in Trunk.toml, and consist of a stage, command and command_arguments:

At the relevant point for each stage, all hooks for that stage are spawned simultaneously. After this, Trunk immediately waits for all the hooks to exit before proceeding, except in the case of the build stage, described further below.

Trunk's build process

This is a brief overview of Trunk's build process for the purpose of describing when hooks are executed. Please note that the exact ordering may change in the future to add new features.

The hook stages correspond to this as follows:

Hook Environment & Execution

All hooks are executed using the same stdin and stdout as trunk. The executable is expected to return an error code of 0 to indicate success. Any other code will be treated as an error and terminate the build process. Additionally, the following environment variables are provided to the process:


As of v0.14.0, Trunk now ships with the ability to automatically reload your web app as the Trunk build pipeline completes.