# Developing Extensions

## Extension Capabilities

Extensions can add the following capabilities to Zed:

- [Languages](./languages.md)
- [Themes](./themes.md)
- [Icon Themes](./icon-themes.md)
- [Slash Commands](./slash-commands.md)
- [Context Servers](./context-servers.md)

## Developing an Extension Locally

Before starting to develop an extension for Zed, be sure to [install Rust via rustup](https://www.rust-lang.org/tools/install).

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

When developing an extension, you can use it in Zed without needing to publish it by installing it as a _dev extension_.

From the extensions page, click the `Install Dev Extension` button and select the directory containing your extension.

If you already have a published extension with the same name installed, your dev extension will override it.

## Directory Structure of a Zed Extension

A Zed extension is a Git repository that contains an `extension.toml`. This file must contain some
basic information about the extension:

```toml
id = "my-extension"
name = "My extension"
version = "0.0.1"
schema_version = 1
authors = ["Your Name <you@example.com>"]
description = "My cool extension"
repository = "https://github.com/your-name/my-zed-extension"
```

In addition to this, there are several other optional files and directories that can be used to add functionality to a Zed extension. An example directory structure of an extension that provides all capabilities is as follows:

```
my-extension/
  extension.toml
  Cargo.toml
  src/
    lib.rs
  languages/
    my-language/
      config.toml
      highlights.scm
  themes/
    my-theme.json
```

## WebAssembly

Procedural parts of extensions are written in Rust and compiled to WebAssembly. To develop an extension that includes custom code, include a `Cargo.toml` like this:

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

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

[dependencies]
zed_extension_api = "0.1.0"
```

Use the latest version of the [`zed_extension_api`](https://crates.io/crates/zed_extension_api) available on crates.io. Make sure it's still [compatible with Zed versions](https://github.com/zed-industries/zed/blob/main/crates/extension_api#compatible-zed-versions) you want to support.