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);

# Cargo.toml
[package]
name = "my-extension"
version = "0.1.0"
edition = "2021"

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

[dependencies]
zed_extension_api = "0.1.0"

Implementation

Complete Example: Documentation Fetcher

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

struct DocsExtension;

impl zed::Extension for DocsExtension {
    fn run_slash_command(
        &self,
        command: SlashCommand,
        args: Vec<String>,
        worktree: Option<&zed::Worktree>,
    ) -> Result<SlashCommandOutput> {
        match command.name.as_str() {
            "docs" => self.fetch_docs(args, worktree),
            "api" => self.fetch_api_reference(args),
            _ => Err(format!("Unknown command: {}", command.name)),
        }
    }

    fn complete_slash_command_argument(
        &self,
        command: SlashCommand,
        _args: Vec<String>,
    ) -> Result<Vec<zed::SlashCommandArgumentCompletion>> {
        match command.name.as_str() {
            "docs" => Ok(vec![
                zed::SlashCommandArgumentCompletion {
                    label: "rust".to_string(),
                    new_text: "rust".to_string(),
                    run_command: true,
                },
                zed::SlashCommandArgumentCompletion {
                    label: "typescript".to_string(),
                    new_text: "typescript".to_string(),
                    run_command: true,
                },
                zed::SlashCommandArgumentCompletion {
                    label: "python".to_string(),
                    new_text: "python".to_string(),
                    run_command: true,
                },
            ]),
            _ => Ok(vec![]),
        }
    }
}

impl DocsExtension {
    fn fetch_docs(
        &self,
        args: Vec<String>,
        worktree: Option<&zed::Worktree>,
    ) -> Result<SlashCommandOutput> {
        if args.is_empty() {
            return Err("docs requires a topic (e.g., /docs rust)".to_string());
        }

        let topic = args.join(" ");
        let docs_url = format!("https://docs.rs/{}", topic);

        // Use worktree context if available
        let context = if let Some(wt) = worktree {
            format!("\nProject: {}", wt.root_path())
        } else {
            String::new()
        };

        let output_text = format!(
            "Documentation for: {}\nURL: {}{}\n\nFetching latest docs...",
            topic, docs_url, context
        );

        Ok(SlashCommandOutput {
            text: output_text.clone(),
            sections: vec![
                SlashCommandOutputSection {
                    range: (0..output_text.len()),
                    label: format!("Docs: {}", topic),
                },
            ],
        })
    }

    fn fetch_api_reference(&self, args: Vec<String>) -> Result<SlashCommandOutput> {
        if args.is_empty() {
            return Err("api requires a library name".to_string());
        }

        let library = &args[0];

        // Execute external command to fetch API docs
        let output = Command::new("curl")
            .args(&["-s", &format!("https://api.github.com/repos/{}/readme", library)])
            .output()
            .map_err(|e| format!("Failed to execute curl: {}", e))?;

        if !output.status.success() {
            return Err("Failed to fetch API documentation".to_string());
        }

        let response = String::from_utf8_lossy(&output.stdout);

        Ok(SlashCommandOutput {
            text: format!("API Reference for {}\n\n{}", library, response),
            sections: vec![],
        })
    }
}

zed::register_extension!(DocsExtension);

Extension Manifest with All Fields

# extension.toml
id = "docs-fetcher"
name = "Documentation Fetcher"
description = "Fetch documentation and API references via slash commands"
version = "1.0.0"
authors = ["Developer Name <[email protected]>"]
repository = "https://github.com/username/docs-fetcher"
license = "MIT"

[slash_commands.docs]
description = "fetch documentation for a topic"
requires_argument = true

[slash_commands.api]
description = "fetch API reference for a library"
requires_argument = true

[slash_commands.help]
description = "show available documentation commands"
requires_argument = false

Development Workflow

1. Setup

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

# Add WASM target
rustup target add wasm32-wasip1

# Create extension directory
mkdir -p ~/.local/share/zed/extensions/my-extension
cd ~/.local/share/zed/extensions/my-extension

2. Build

# Compile to WASM
cargo build --release --target wasm32-wasip1

# WASM output location
# target/wasm32-wasip1/release/my_extension.wasm

3. Test Locally

# Zed automatically loads extensions from:
# macOS: ~/Library/Application Support/Zed/extensions/
# Linux: ~/.local/share/zed/extensions/

# Copy extension files
cp extension.toml ~/Library/Application\ Support/Zed/extensions/my-extension/
cp target/wasm32-wasip1/release/my_extension.wasm ~/Library/Application\ Support/Zed/extensions/my-extension/extension.wasm

# Restart Zed to load extension

4. Publish

# Extensions published via PR to zed-industries/extensions
# https://github.com/zed-industries/extensions

# Fork the repository
git clone https://github.com/zed-industries/extensions
cd extensions

# Add your extension
mkdir extensions/my-extension
cp -r ~/path/to/my-extension/* extensions/my-extension/

# Create PR with extension metadata
git checkout -b add-my-extension
git add extensions/my-extension
git commit -m "Add my-extension: Custom slash commands"
git push origin add-my-extension

License Requirements

Required licenses (as of October 1st, 2025):

• MIT
• Apache-2.0
• BSD-3-Clause
• GPL-3.0

Extensions with other licenses will be rejected during review.

Slash Command API Reference

Types

// Command input
struct SlashCommand {
    name: String,
    // Additional metadata
}

// Command output
struct SlashCommandOutput {
    text: String,
    sections: Vec<SlashCommandOutputSection>,
}

struct SlashCommandOutputSection {
    range: (usize, usize),  // Character range in text
    label: String,          // Section label for UI
}

// Argument completion
struct SlashCommandArgumentCompletion {
    label: String,        // Display in completion menu
    new_text: String,     // Insert when selected
    run_command: bool,    // Execute immediately after selection
}

Methods

trait Extension {
    // Required for slash commands
    fn run_slash_command(
        &self,
        command: SlashCommand,
        args: Vec<String>,
        worktree: Option<&Worktree>,
    ) -> Result<SlashCommandOutput, String>;

    // Optional: Argument autocompletion
    fn complete_slash_command_argument(
        &self,
        command: SlashCommand,
        args: Vec<String>,
    ) -> Result<Vec<SlashCommandArgumentCompletion>, String> {
        Ok(vec![])
    }
}

Common Mistakes

Mistake	Why It Fails	Fix
Wrong crate type	WASM compilation fails	Use crate-type = ["cdylib"] in Cargo.toml
Missing error handling	Extension crashes	Return Err(String) for failures
Not validating args	Silent failures	Check args.is_empty() for required args
Hardcoded paths	Extension not portable	Use relative paths or worktree context
Missing default case	Unhandled commands crash	Add _ => Err(...) in match
Unlicensed extension	Rejected by registry	Include approved license in extension.toml
Blocking operations	Freezes Zed UI	Use async or spawn threads for long operations

Advanced Features

Using Worktree Context

fn run_slash_command(
    &self,
    command: SlashCommand,
    args: Vec<String>,
    worktree: Option<&zed::Worktree>,
) -> Result<SlashCommandOutput> {
    if let Some(wt) = worktree {
        let project_root = wt.root_path();
        let config_path = format!("{}/config.json", project_root);

        // Read project-specific config
        let config = std::fs::read_to_string(config_path)
            .map_err(|e| format!("Failed to read config: {}", e))?;

        // Use config in command logic
    }

    // Continue command execution
}

Output Sections for Structured Results

let output_text = format!(
    "# Results\n\n## Section 1\nContent here\n\n## Section 2\nMore content"
);

Ok(SlashCommandOutput {
    text: output_text.clone(),
    sections: vec![
        SlashCommandOutputSection {
            range: (0..12),        // "# Results"
            label: "Header".to_string(),
        },
        SlashCommandOutputSection {
            range: (14..40),       // "## Section 1\nContent here"
            label: "Section 1".to_string(),
        },
        SlashCommandOutputSection {
            range: (42..output_text.len()),
            label: "Section 2".to_string(),
        },
    ],
})

Real-World Impact

Productivity: Custom /deploy command deploys directly from Assistant panel

Documentation: /docs rust Vec fetches Rust Vec documentation without leaving editor

Integration: /gh issue 123 fetches GitHub issue details inline

Workflow: /analyze-deps shows dependency tree and suggests updates

---

Schema Reference: packages/converters/schemas/zed-extension.schema.json

Documentation: https://zed.dev/docs/extensions/developing-extensions

Example Extension: https://github.com/zed-industries/zed/tree/main/extensions/slash-commands-example