> ## 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.
# Set up Rust for FastEdge
The Legacy Rust SDK is based on the `fastedge` crate, Gcore's original Rust library for FastEdge HTTP applications. Most existing FastEdge applications written in Rust use this SDK. Use this setup when working with existing applications built on the `fastedge` crate or when maintaining code that still targets `wasm32-wasip1`.
The crate provides the `#[fastedge::http]` entry-point macro together with APIs for environment variables, secrets, key-value storage, dictionary access, and cache integration.
[Rust and Cargo](https://rustup.rs) are required. On Windows, also install [Visual Studio Build Tools](https://visualstudio.microsoft.com/downloads/#build-tools-for-visual-studio-2022) with the **Desktop development with C++** workload.
For new applications, the [Modern Rust SDK](/fastedge/getting-started/setup-rust-modern) (`wstd`, `wasm32-wasip2`) is the recommended direction — it uses the WASI-HTTP standard and reduces dependency on Gcore-specific tooling.
## Add the WebAssembly target
The Legacy SDK compiles to `wasm32-wasip1`. Add the target once — it applies to all future builds:
```sh theme={null}
rustup target add wasm32-wasip1
```
## Configure a project
FastEdge applications compile to WebAssembly libraries rather than standalone executables. Two changes from the Cargo defaults are needed: the output type must be `cdylib`, and the `fastedge` crate must be listed as a dependency.
1. Create the library crate:
```sh theme={null}
cargo new --lib my-app
cd my-app
```
2. Replace the contents of `Cargo.toml`:
```toml theme={null}
[package]
name = "my_app"
version = "0.1.0"
edition = "2021"
[lib]
crate-type = ["cdylib"]
[dependencies]
fastedge = "0.4"
anyhow = "1.0"
```
`crate-type = ["cdylib"]` changes the output to a format the FastEdge runtime can load. `fastedge = "0.4"` provides the entry-point macro and access to FastEdge-specific APIs. `anyhow` is used for error handling in the verification example below.
## Verify the toolchain
A minimal handler is enough to confirm the toolchain produces a valid WebAssembly binary. Replace `src/lib.rs`:
```rust theme={null}
use fastedge::body::Body;
use fastedge::http::{Request, Response, StatusCode, Error};
#[fastedge::http]
fn main(_req: Request) -> Result, Error> {
Response::builder()
.status(StatusCode::OK)
.body(Body::from("OK"))
}
```
Build it:
```sh theme={null}
cargo build --release --target wasm32-wasip1
```
The first build downloads dependencies and takes one to two minutes. When it completes without errors, the toolchain is ready — the compiled binary is at `./target/wasm32-wasip1/release/my_app.wasm`. That file can be uploaded to FastEdge directly or used as the starting point for the next tutorial.