ASPX for Zed

Syntax highlighting for ASP.NET WebForms files (.aspx, .ascx, .master, .asmx, .ashx) in the Zed editor, with HTML and C# embedded inside server tags.

Install

From the Zed extension registry

1. Open Zed.
2. Open the command palette (cmd-shift-p / ctrl-shift-p) and run zed: extensions.
3. Search for ASPX and click Install.

Zed will then highlight any file with an ASPX file extension automatically.

As a dev extension (from source)

1. Clone this repository.
2. In Zed, run zed: install dev extension from the command palette.
3. Select the cloned folder.

Recommended companion extension

Install the C# extension too. Zed doesn't ship C# in core, and this extension injects C# into <% %>, <%= %>, and <%# %> server tags — the injection only takes effect once a language called "CSharp" is registered, which happens when the C# extension is installed.

The HTML injection that handles page markup, embedded <script>, and embedded <style> is built into Zed and needs no extra setup.

What you get

• File-type detection for .aspx, .ascx, .master, .asmx, .ashx.
• Page content highlighted as HTML (via language injection).
• HTML regions are combined before injection, so tags split by ASPX islands such as <h2><%= Name %></h2> still highlight as one coherent HTML tree.
• Code inside <% ... %> and <%= ... %> server tags highlighted as C# (also via injection).
• Plain server code blocks are combined before C# injection, which improves split control-flow such as <% if (...) { %> ... <% } %>.
• Data-binding expressions <%# Eval(...) %> highlighted as C# (rather than as comments — the upstream grammar treats <%# as an EJS-style comment; this extension corrects that for ASP.NET).
• Page directives <%@ Page ... %> highlighted as preprocessor directives rather than being mis-parsed as C# expressions.
• Server-side comments <%-- ... --%> highlighted as comments.
• editor: toggle comments uses <%-- --%> as the comment delimiter.

Known limitations

This extension uses Tree-sitter's embedded-template grammar, which was designed for ERB/EJS-style templates. That grammar covers the most common ASPX syntax but does not natively understand every ASP.NET-specific construct. Specifically:

• <%: ... %> (HTML-encoded output, ASP.NET 4+) is not specially tokenised — it's parsed as a generic code block.
• <%$ ... %> (expression builders, e.g. <%$ ConnectionStrings:MyDb %>) is highlighted as an ASPX expression builder, but is not deeply parsed.
• <%@ ... %> directive bodies are highlighted as directives as a whole; the borrowed grammar does not expose individual attributes like Language or CodeBehind for separate colouring.
• <asp:Control runat="server"> server controls are highlighted by the HTML injection — they look like XML tags, with no extra semantics on attributes like runat, OnClick, etc.
• SQL inside ASPX attributes such as SelectCommand="SELECT ..." remains an HTML attribute string. Highlighting that as SQL would require either a custom ASPX grammar that exposes those attributes or deeper HTML/SQL injection rules.

A proper ASP.NET-specific Tree-sitter grammar would address all of the above, but is a larger separate project. PRs welcome.

License

MIT.

The bundled grammar is fetched at build time from tree-sitter/tree-sitter-embedded-template and is licensed separately under the MIT license.