diff --git a/crates/service/Cargo.toml b/crates/service/Cargo.toml
index b5f0824a..1b04e03f 100644
--- a/crates/service/Cargo.toml
+++ b/crates/service/Cargo.toml
@@ -18,7 +18,9 @@ rustc-hash = "2.0"
 salsa = "0.16"
 serde.workspace = true
 smallvec = "1.13"
-wat_formatter = { path = "../formatter", version = "0.1" }
+wat_formatter = { path = "../formatter", version = "0.1", features = [
+    "config_serde",
+] }
 wat_parser = { path = "../parser", version = "0.1" }
 wat_syntax = { path = "../syntax", version = "0.1" }
 
diff --git a/crates/service/src/config.rs b/crates/service/src/config.rs
index c6a66b3b..c60d3d62 100644
--- a/crates/service/src/config.rs
+++ b/crates/service/src/config.rs
@@ -3,5 +3,6 @@ use serde::{Deserialize, Serialize};
 #[derive(Clone, Debug, Default, Serialize, Deserialize)]
 /// Language service configuration. This can be different for each document.
 pub struct ServiceConfig {
-    //
+    /// Configuration about formatting.
+    pub format: wat_formatter::config::LanguageOptions,
 }
diff --git a/crates/service/src/features/formatting.rs b/crates/service/src/features/formatting.rs
index e6f24dc4..a33bba6a 100644
--- a/crates/service/src/features/formatting.rs
+++ b/crates/service/src/features/formatting.rs
@@ -4,7 +4,7 @@ use lsp_types::{
     DocumentFormattingParams, DocumentRangeFormattingParams, FormattingOptions, TextEdit,
 };
 use rowan::ast::AstNode;
-use wat_formatter::config::{FormatOptions, LayoutOptions};
+use wat_formatter::config::{FormatOptions, LanguageOptions, LayoutOptions};
 use wat_syntax::{ast::Root, SyntaxNode};
 
 impl LanguageService {
@@ -13,7 +13,16 @@ impl LanguageService {
         let uri = self.uri(params.text_document.uri);
         let line_index = self.line_index(uri);
         let root = Root::cast(SyntaxNode::new_root(self.root(uri)))?;
-        let formatted = wat_formatter::format(&root, &build_options(&params.options));
+        let formatted = wat_formatter::format(
+            &root,
+            &build_options(
+                &params.options,
+                self.configs
+                    .get(&uri)
+                    .map(|config| config.format.clone())
+                    .unwrap_or_default(),
+            ),
+        );
         let text_edit = TextEdit {
             range: helpers::rowan_range_to_lsp_range(&line_index, root.syntax().text_range()),
             new_text: formatted,
@@ -28,7 +37,13 @@ impl LanguageService {
         let root = Root::cast(SyntaxNode::new_root(self.root(uri)))?;
         let (formatted, range) = wat_formatter::format_range(
             &root,
-            &build_options(&params.options),
+            &build_options(
+                &params.options,
+                self.configs
+                    .get(&uri)
+                    .map(|config| config.format.clone())
+                    .unwrap_or_default(),
+            ),
             helpers::lsp_range_to_rowan_range(&line_index, params.range)?,
             &line_index,
         )?;
@@ -40,13 +55,13 @@ impl LanguageService {
     }
 }
 
-fn build_options(options: &FormattingOptions) -> FormatOptions {
+fn build_options(layout: &FormattingOptions, language: LanguageOptions) -> FormatOptions {
     FormatOptions {
         layout: LayoutOptions {
-            indent_width: options.tab_size as usize,
-            use_tabs: !options.insert_spaces,
+            indent_width: layout.tab_size as usize,
+            use_tabs: !layout.insert_spaces,
             ..Default::default()
         },
-        language: Default::default(),
+        language,
     }
 }
diff --git a/crates/service/tests/formatting/full.rs b/crates/service/tests/formatting/full.rs
index 1c07ff58..c5a7a594 100644
--- a/crates/service/tests/formatting/full.rs
+++ b/crates/service/tests/formatting/full.rs
@@ -1,6 +1,6 @@
 use insta::assert_json_snapshot;
 use lsp_types::{DocumentFormattingParams, FormattingOptions, TextDocumentIdentifier, Uri};
-use wat_service::LanguageService;
+use wat_service::{LanguageService, ServiceConfig};
 
 fn create_params(uri: Uri, options: FormattingOptions) -> DocumentFormattingParams {
     DocumentFormattingParams {
@@ -78,3 +78,30 @@ fn tab() {
     ));
     assert_json_snapshot!(response);
 }
+
+#[test]
+fn format_comments() {
+    let uri = "untitled:test".parse::<Uri>().unwrap();
+    let source = ";;comment";
+    let mut service = LanguageService::default();
+    service.commit(uri.clone(), source.into());
+    service.set_config(
+        uri.clone(),
+        ServiceConfig {
+            format: wat_formatter::config::LanguageOptions {
+                format_comments: true,
+                ..Default::default()
+            },
+            ..Default::default()
+        },
+    );
+    let response = service.formatting(create_params(
+        uri,
+        FormattingOptions {
+            tab_size: 2,
+            insert_spaces: true,
+            ..Default::default()
+        },
+    ));
+    assert_json_snapshot!(response);
+}
diff --git a/crates/service/tests/formatting/range.rs b/crates/service/tests/formatting/range.rs
index 1082c795..ab26c4ab 100644
--- a/crates/service/tests/formatting/range.rs
+++ b/crates/service/tests/formatting/range.rs
@@ -2,7 +2,7 @@ use insta::assert_json_snapshot;
 use lsp_types::{
     DocumentRangeFormattingParams, FormattingOptions, Position, Range, TextDocumentIdentifier, Uri,
 };
-use wat_service::LanguageService;
+use wat_service::{LanguageService, ServiceConfig};
 
 fn create_params(uri: Uri, range: Range) -> DocumentRangeFormattingParams {
     DocumentRangeFormattingParams {
@@ -63,3 +63,32 @@ fn overlap() {
     ));
     assert_json_snapshot!(response);
 }
+
+#[test]
+fn format_comments() {
+    let uri = "untitled:test".parse::<Uri>().unwrap();
+    let source = "
+(module
+  (func
+    ;;comment
+  )
+)
+";
+    let mut service = LanguageService::default();
+    service.commit(uri.clone(), source.into());
+    service.set_config(
+        uri.clone(),
+        ServiceConfig {
+            format: wat_formatter::config::LanguageOptions {
+                format_comments: true,
+                ..Default::default()
+            },
+            ..Default::default()
+        },
+    );
+    let response = service.range_formatting(create_params(
+        uri,
+        Range::new(Position::new(3, 4), Position::new(3, 13)),
+    ));
+    assert_json_snapshot!(response);
+}
diff --git a/crates/service/tests/formatting/snapshots/features__formatting__full__format_comments.snap b/crates/service/tests/formatting/snapshots/features__formatting__full__format_comments.snap
new file mode 100644
index 00000000..4e20a6a2
--- /dev/null
+++ b/crates/service/tests/formatting/snapshots/features__formatting__full__format_comments.snap
@@ -0,0 +1,19 @@
+---
+source: crates/service/tests/formatting/full.rs
+expression: response
+---
+[
+  {
+    "range": {
+      "start": {
+        "line": 0,
+        "character": 0
+      },
+      "end": {
+        "line": 0,
+        "character": 9
+      }
+    },
+    "newText": ";; comment\n"
+  }
+]
diff --git a/crates/service/tests/formatting/snapshots/features__formatting__range__format_comments.snap b/crates/service/tests/formatting/snapshots/features__formatting__range__format_comments.snap
new file mode 100644
index 00000000..f5ebdf41
--- /dev/null
+++ b/crates/service/tests/formatting/snapshots/features__formatting__range__format_comments.snap
@@ -0,0 +1,19 @@
+---
+source: crates/service/tests/formatting/range.rs
+expression: response
+---
+[
+  {
+    "range": {
+      "start": {
+        "line": 2,
+        "character": 2
+      },
+      "end": {
+        "line": 4,
+        "character": 3
+      }
+    },
+    "newText": "(func ;; comment\n  )"
+  }
+]