Getting Started with Extensions

Glass extensions allow you to extend the editor with custom languages, themes, debuggers, slash commands, and more. Extensions are written in Rust, compiled to WebAssembly, and distributed through the extension registry.

What You Can Build

Extensions can provide:

Languages: Add support for new programming languages with syntax highlighting, language servers, and more
Themes: Create custom color schemes and icon themes
Debuggers: Integrate Debug Adapter Protocol (DAP) servers
Slash Commands: Add custom commands to the Assistant panel
MCP Servers: Expose Model Context Protocol servers

Prerequisites

Before developing extensions, you need:

Install Rust via rustup

Extensions are written in Rust and compiled to WebAssembly. Install Rust using rustup:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Rust must be installed via rustup. If you have Rust installed via homebrew or another method, installing dev extensions will not work.

Add the WASM target

Add the WebAssembly compilation target:

rustup target add wasm32-wasip1

Creating Your First Extension

Create the extension directory

Create a new directory for your extension:

mkdir my-extension
cd my-extension

Create extension.toml

Every extension requires an extension.toml manifest:

id = "my-extension"
name = "My Extension"
version = "0.0.1"
schema_version = 1
authors = ["Your Name <[email protected]>"]
description = "Example extension"
repository = "https://github.com/your-name/my-extension"

If you’re building a theme extension, suffix the ID with -theme (e.g., monokai-theme).

Create Cargo.toml

For extensions with custom code, create a Cargo.toml:

[package]
name = "my-extension"
version = "0.0.1"
edition = "2021"

[lib]
crate-type = ["cdylib"]

[dependencies]
zed_extension_api = "0.7.0"

Use the latest version of zed_extension_api from crates.io. Check compatibility with Glass versions.

Create src/lib.rs

Implement the Extension trait in src/lib.rs:

use zed_extension_api as zed;

struct MyExtension;

impl zed::Extension for MyExtension {
    fn new() -> Self {
        Self
    }
}

zed::register_extension!(MyExtension);

Extension Structure

A complete extension might look like:

my-extension/
  extension.toml          # Extension manifest
  Cargo.toml             # Rust package configuration
  LICENSE                # Required for publishing
  src/
    lib.rs               # Extension implementation
  languages/
    my-language/
      config.toml        # Language configuration
      highlights.scm     # Syntax highlighting
  themes/
    my-theme.json        # Theme definition

Installing as a Dev Extension

To test your extension locally without publishing:

Open Glass Extensions

Press Cmd+Shift+P (macOS) or Ctrl+Shift+P (Linux/Windows) and run Extensions: Install Dev Extension.

Select your extension directory

Choose the directory containing your extension.toml file.

Check the Extensions page

The published version (if any) will be replaced with your dev extension. The Extensions page will show “Overridden by dev extension”.

Debugging Extensions

# View detailed logs
open ~/Library/Logs/Glass/Glass.log

# Run Glass from terminal for verbose output
/Applications/Glass.app/Contents/MacOS/glass --foreground

The --foreground flag shows INFO-level logs including println! and dbg! output from your extension.

Extension API Reference

The Extension trait provides methods for:

language_server_command: Return the command to start a language server
language_server_initialization_options: Provide LSP initialization options
language_server_workspace_configuration: Provide workspace configuration
run_slash_command: Execute custom slash commands
get_dap_binary: Return debug adapter binary and configuration
complete_slash_command_argument: Provide completions for slash command arguments

See the zed_extension_api documentation for the complete API.

Next Steps

Language Extensions

Add support for new programming languages

Theme Extensions

Create custom color schemes

Slash Commands

Build custom Assistant commands

Debugging Extensions

Integrate debug adapters

Example Extensions

Explore these examples in the Glass repository:

HTML Extension - Language server integration
Slash Commands Example - Custom slash commands
Test Extension - Complete extension features

Using Extensions

Building Extensions

Extension API

Getting Started with Extensions