creating-zed-extensions

Creating Zed Extensions

Overview

Zed extensions are Rust programs compiled to WebAssembly that can provide slash commands, language support, themes, grammars, and MCP servers. Extensions implement the zed::Extension trait and are distributed via Zed's extension registry.

When to Use

Create a Zed extension when:

• Adding custom slash commands to the Assistant (/deploy, /analyze, /fetch-docs)
• Providing language support (syntax highlighting, LSP, formatting)
• Creating custom color themes
• Integrating external tools via slash commands
• Providing MCP server integrations

Don't create for:

• Simple rules or instructions (use .rules files)
• One-time scripts (use terminal)
• Project-specific configuration (use .zed/settings.json)

Quick Reference

Extension Structure

my-extension/
├── Cargo.toml              # Rust manifest
├── extension.toml          # Extension metadata
└── src/
    └── lib.rs             # Extension implementation

Minimal Slash Command Extension

# extension.toml
id = "my-commands"
name = "My Commands"
version = "0.1.0"
authors = ["Your Name"]
repository = "https://github.com/username/my-commands"
license = "MIT"

[slash_commands.echo]
description = "echoes the provided input"
requires_argument = true

[slash_commands.greet]
description = "greets the user"
requires_argument = false

// src/lib.rs
use zed_extension_api::{self as zed, Result, SlashCommand, SlashCommandOutput};

struct MyExtension;

impl zed::Extension for MyExtension {
    fn run_slash_command(
        &self,
        command: SlashCommand,
        args: Vec<String>,
        _worktree: Option<&zed::Worktree>,
    ) -> Result<SlashCommandOutput> {
        match command.name.as_str() {
            "echo" => {
                if args.is_empty() {
                    return Err("echo requires an argument".to_string());
                }
                Ok(SlashCommandOutput {
                    text: args.join(" "),
                    sections: vec![],
                })
            }
            "greet" => {
                Ok(SlashCommandOutput {
                    text: "Hello! How can I help you today?".to_string(),
                    sections: vec![],
                })
            }
            _ => Err(format!("Unknown command: {}", command.name)),
        }
    }
}

zed::register_extension!(MyExtension);