> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gcore.com/llms.txt
> Use this file to discover all available pages before exploring further.

# FastEdge extension for VS Code

The FastEdge extension for VS Code compiles Rust, JavaScript, or AssemblyScript source into a Wasm binary, serves it locally through a bundled debugger, and opens a request panel inside the editor for sending test requests and inspecting responses — no separate build tools or terminal commands required.

<Info>
  The build toolchain for the target language must be installed:

  * Rust: `rustup target add wasm32-wasip1`
  * JavaScript: `@gcoredev/fastedge-sdk-js`
  * AssemblyScript: `assemblyscript`, `@assemblyscript/wasi-shim`, and `@gcoredev/proxy-wasm-sdk-as`
</Info>

## Supported languages and app types

The extension builds both FastEdge application types, each tied to a specific language and SDK:

| App type | Languages            | SDK                                                                                                                                        |
| -------- | -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ |
| HTTP     | Rust, JavaScript     | [FastEdge-sdk-rust](https://github.com/G-Core/FastEdge-sdk-rust), [FastEdge-sdk-js](https://github.com/G-Core/FastEdge-sdk-js)             |
| CDN      | Rust, AssemblyScript | [proxy-wasm-sdk-rust](https://github.com/proxy-wasm/proxy-wasm-rust-sdk), [proxy-wasm-sdk-as](https://github.com/G-Core/proxy-wasm-sdk-as) |

Once a project is opened, the extension detects its language automatically, from whichever signal is present: a VS Code language ID of `rust` for Rust, an `asconfig.json` file at the project root for AssemblyScript, or a JS/TS file without `asconfig.json` for JavaScript.

## Install the extension

Install [FastEdge Launcher](https://marketplace.visualstudio.com/items?itemName=G-CoreLabsSA.fastedge) from the Visual Studio Marketplace.

<Info>
  Editors built on the VS Code extension host without access to the Visual Studio Marketplace can install the OS-specific `.vsix` package instead, downloaded from [GitHub releases](https://github.com/G-Core/FastEdge-vscode/releases): `{editor-cli} --install-extension fastedge-{os}-{version}.vsix`.
</Info>

## Initialize a workspace

A `.vscode/launch.json` file is required before debugging. Create one automatically from the Command Palette (`Ctrl+Shift+P`): `FastEdge: Initialize workspace (create launch.json)`.

```json theme={null}
{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "FastEdge App Runner: Launch",
      "type": "fastedge",
      "request": "launch",
      "entrypoint": "file"
    }
  ]
}
```

The `entrypoint` field is the only value the extension reads from `launch.json`:

| Value            | Behavior                                                         |
| ---------------- | ---------------------------------------------------------------- |
| `file` (default) | Builds the active editor file                                    |
| `package`        | Builds from the `main` field in `package.json` — JavaScript only |

## Debug an application

Press `F5`, or run `Debug: Start Debug` from the Command Palette, to build the active file and open the debugger. Each running app gets an isolated local server on a port between 5179 and 5188, so multiple apps in the same workspace can be debugged at the same time.

The debugger opens as a panel inside the editor for building a request — URL, method, headers, body — sending it to the running app, and inspecting the response. Test configurations can be saved and reloaded from the same panel.

| Command                             | Description                                                       |
| ----------------------------------- | ----------------------------------------------------------------- |
| Debug: FastEdge App (Current File)  | Builds the active file and starts the debugger                    |
| Debug: FastEdge App (Package Entry) | Builds from the `package.json` main field and starts the debugger |
| FastEdge: Initialize workspace      | Creates `.vscode/launch.json` with the default configuration      |
| FastEdge (Generate mcp.json)        | Adds the FastEdge MCP server to the workspace                     |
| FastEdge (Setup Codespace Secrets)  | Configures GitHub Codespaces secrets for FastEdge                 |

Two more actions are available from the file explorer's right-click menu instead of the Command Palette: **FastEdge: Load in Debugger** on a `.wasm` file loads a precompiled binary directly, and **FastEdge: Load Config in Debugger** on a `*test.json` file loads a saved test configuration.

## Configure runtime values

Environment variables, secrets, and request or response headers are set through test configuration files, not `launch.json`. The debugger panel writes and reads these controls from a `fastedge-config.test.json` file in the app root.

<p>As an alternative, the extension auto-discovers `.env` files in the app root. Add both to `.gitignore` before storing secrets in either:</p>

```
.vscode/
.env
.env.*
.fastedge-debug/
```

## Connect the FastEdge MCP server

Beyond local debugging, the extension can also configure the FastEdge MCP server for AI-assisted workflows. AI clients that support the Model Context Protocol can reach the server directly from VS Code. Running `FastEdge (Generate mcp.json)` from the Command Palette writes a working server configuration into the workspace — the same Docker-based setup described in [AI-assisted development](/fastedge/local-development/ai-assisted-development#connect-other-ai-clients) — without editing the JSON file by hand.

## Settings

Two settings control the bundled debugger and its generated MCP configuration:

| Setting               | Description                                                                                                            |
| --------------------- | ---------------------------------------------------------------------------------------------------------------------- |
| `fastedge.cliVersion` | Version of the bundled debugger — read-only                                                                            |
| `fastedge.apiUrl`     | API host the generated MCP configuration points to — defaults to `https://api.gcore.com`; override for preprod testing |