diff --git a/Cargo.lock b/Cargo.lock
index 83c1d95..8ae478d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -11,6 +11,17 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "alejandra"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2523e3312f47f4b28c443249c1d25fe7a71e4719198a8889fcc41a155032cb7f"
+dependencies = [
+ "mimalloc",
+ "rnix",
+ "rowan",
+]
+
 [[package]]
 name = "ansi_term"
 version = "0.12.1"
@@ -61,6 +72,12 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "cc"
+version = "1.0.73"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2fff2a6927b3bb87f9595d67196a70493f627687a71d87a0d692242c33f58c11"
+
 [[package]]
 name = "cfg-if"
 version = "0.1.10"
@@ -295,6 +312,15 @@ version = "0.2.126"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "349d5a591cd28b49e1d1037471617a32ddcda5731b99419008085f72d5a53836"
 
+[[package]]
+name = "libmimalloc-sys"
+version = "0.1.25"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "11ca136052550448f55df7898c6dbe651c6b574fe38a0d9ea687a9f8088a2e2c"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "log"
 version = "0.4.17"
@@ -356,6 +382,15 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "mimalloc"
+version = "0.1.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2f64ad83c969af2e732e907564deb0d0ed393cec4af80776f77dd77a1a427698"
+dependencies = [
+ "libmimalloc-sys",
+]
+
 [[package]]
 name = "nixpkgs-fmt-rnix"
 version = "1.2.0"
@@ -462,6 +497,7 @@ dependencies = [
 name = "rnix-lsp"
 version = "0.3.0-dev"
 dependencies = [
+ "alejandra",
  "dirs",
  "env_logger",
  "gc",
diff --git a/Cargo.toml b/Cargo.toml
index 39d5233..3794f7b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -20,10 +20,11 @@ log = "0.4.17"
 lsp-server = "0.6.0"
 lsp-types = { version = "0.93.0", features = ["proposed"] }
 regex = "1.5.6"
+alejandra = { version = "1.5.0", optional = true }
 rnix = "0.10.2"
 serde = "1.0.138"
 serde_json = "1.0.82"
-nixpkgs-fmt-rnix = "1.2.0"
+nixpkgs-fmt-rnix = { version = "1.2.0", optional = true }
 
 [dev-dependencies]
 stoppable_thread = "0.2.1"
@@ -32,7 +33,7 @@ maplit = "1"
 [features]
 
 # Set this to ["verbose"] when debugging
-default = []
+default = [ "nixpkgs-fmt-rnix" ]
 
 # Enable showing internal errors via editor UI, such as via hover popups.
 # This can be helpful for debugging, but we don't want the evaluator to
diff --git a/src/main.rs b/src/main.rs
index 6f92189..88c8f0a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -209,16 +209,40 @@ impl App {
             let document_links = self.document_links(&params).unwrap_or_default();
             self.reply(Response::new_ok(id, document_links));
         } else if let Some((id, params)) = cast::<Formatting>(&mut req) {
-            let changes = if let Some((ast, code, _)) = self.files.get(&params.text_document.uri) {
-                let fmt = nixpkgs_fmt::reformat_node(&ast.node());
-                vec![TextEdit {
-                    range: utils::range(&code, TextRange::up_to(ast.node().text().len())),
-                    new_text: fmt.text().to_string(),
-                }]
+            if let Some((ast, code, _)) = self.files.get(&params.text_document.uri) {
+                let node = ast.node();
+                let range = utils::range(&code, TextRange::up_to(node.text().len()));
+                if cfg!(feature = "alejandra") {
+                    #[cfg(feature = "alejandra")]
+                    match alejandra::format::in_memory(
+                        params.text_document.uri.to_string(),
+                        code.to_string(),
+                    ) {
+                        (alejandra::format::Status::Changed(true), new_text) => {
+                            self.reply(Response::new_ok(id, vec![TextEdit { range, new_text }]))
+                        }
+                        (alejandra::format::Status::Changed(false), _) => {
+                            self.reply(Response::new_ok(id, ()))
+                        }
+                        (alejandra::format::Status::Error(e), _) => {
+                            self.reply(Response::new_err(id, ErrorCode::InternalError as i32, e))
+                        }
+                    }
+                } else if cfg!(feature = "nixpkgs-fmt-rnix") {
+                    #[cfg(feature = "nixpkgs-fmt-rnix")]
+                    self.reply(Response::new_ok(
+                        id,
+                        vec![TextEdit {
+                            range,
+                            new_text: nixpkgs_fmt::reformat_node(&node).text().to_string(),
+                        }],
+                    ));
+                } else {
+                    self.reply(Response::new_ok(id, ()))
+                }
             } else {
-                Vec::new()
-            };
-            self.reply(Response::new_ok(id, changes));
+                self.reply(Response::new_ok(id, ()))
+            }
         } else if let Some((id, params)) = cast::<HoverRequest>(&mut req) {
             if let Some((range, markdown)) = self.hover(params) {
                 self.reply(Response::new_ok(