diff --git a/crates/agent/src/agent/tools/fs_write.rs b/crates/agent/src/agent/tools/fs_write.rs
index 2b99f81ed3..00a697252a 100644
--- a/crates/agent/src/agent/tools/fs_write.rs
+++ b/crates/agent/src/agent/tools/fs_write.rs
@@ -220,7 +220,10 @@ impl StrReplace {
             .await
             .map_err(|e| ToolExecutionError::io(format!("failed to read {}", path.to_string_lossy()), e))?;
 
-        let matches = file.match_indices(&self.old_str).collect::<Vec<_>>();
+        let line_ending = if file.contains("\r\n") { "\r\n" } else { "\n" };
+        let old_str = self.old_str.replace("\r\n", "\n").replace('\n', line_ending);
+        let new_str = self.new_str.replace("\r\n", "\n").replace('\n', line_ending);
+        let matches = file.match_indices(&old_str).collect::<Vec<_>>();
         match matches.len() {
             0 => {
                 return Err(ToolExecutionError::Custom(format!(
@@ -229,7 +232,7 @@ impl StrReplace {
                 )));
             },
             1 => {
-                let file = file.replacen(&self.old_str, &self.new_str, 1);
+                let file = file.replacen(&old_str, &new_str, 1);
                 tokio::fs::write(path, file)
                     .await
                     .map_err(|e| ToolExecutionError::io(format!("failed to read {}", path.to_string_lossy()), e))?;
@@ -240,7 +243,7 @@ impl StrReplace {
                         "{x} occurrences of old_str were found when only 1 is expected"
                     )));
                 }
-                let file = file.replace(&self.old_str, &self.new_str);
+                let file = file.replace(&old_str, &new_str);
                 tokio::fs::write(path, file)
                     .await
                     .map_err(|e| ToolExecutionError::io(format!("failed to read {}", path.to_string_lossy()), e))?;
@@ -421,6 +424,25 @@ mod tests {
         assert_eq!(content, "baz bar baz");
     }
 
+    #[tokio::test]
+    async fn test_str_replace_preserves_crlf() {
+        let test_base = TestBase::new()
+            .await
+            .with_file(("test.txt", "first\r\nsecond\r\nthird"))
+            .await;
+
+        let tool = FsWrite::StrReplace(StrReplace {
+            path: test_base.join("test.txt").to_string_lossy().to_string(),
+            old_str: "first\nsecond".to_string(),
+            new_str: "one\ntwo".to_string(),
+            replace_all: false,
+        });
+
+        assert!(tool.execute(None, &test_base).await.is_ok());
+        let content = tokio::fs::read_to_string(test_base.join("test.txt")).await.unwrap();
+        assert_eq!(content, "one\r\ntwo\r\nthird");
+    }
+
     #[tokio::test]
     async fn test_str_replace_no_match() {
         let test_base = TestBase::new().await.with_file(("test.txt", "hello world")).await;
diff --git a/crates/chat-cli/src/cli/chat/tools/fs_write.rs b/crates/chat-cli/src/cli/chat/tools/fs_write.rs
index 09a64058a1..af24b7138a 100644
--- a/crates/chat-cli/src/cli/chat/tools/fs_write.rs
+++ b/crates/chat-cli/src/cli/chat/tools/fs_write.rs
@@ -133,7 +133,10 @@ impl FsWrite {
             },
             FsWrite::StrReplace { old_str, new_str, .. } => {
                 let file = os.fs.read_to_string(&path).await?;
-                let matches = file.match_indices(old_str).collect::<Vec<_>>();
+                let line_ending = if file.contains("\r\n") { "\r\n" } else { "\n" };
+                let old_str = old_str.replace("\r\n", "\n").replace('\n', line_ending);
+                let new_str = new_str.replace("\r\n", "\n").replace('\n', line_ending);
+                let matches = file.match_indices(&old_str).collect::<Vec<_>>();
                 queue!(
                     output,
                     style::Print("Updating: "),
@@ -145,7 +148,7 @@ impl FsWrite {
                 match matches.len() {
                     0 => return Err(eyre!("no occurrences of \"{old_str}\" were found")),
                     1 => {
-                        let file = file.replacen(old_str, new_str, 1);
+                        let file = file.replacen(&old_str, &new_str, 1);
                         os.fs.write(&path, file).await?;
                     },
                     x => return Err(eyre!("{x} occurrences of old_str were found when only 1 is expected")),
@@ -1068,6 +1071,29 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn test_fs_write_tool_str_replace_preserves_crlf() {
+        let os = Os::new().await.unwrap();
+        let mut stdout = std::io::stdout();
+        let mut line_tracker = HashMap::new();
+        let path = "/crlf.txt";
+        os.fs.write(path, "first\r\nsecond\r\nthird").await.unwrap();
+
+        let v = serde_json::json!({
+            "path": path,
+            "command": "str_replace",
+            "old_str": "first\nsecond",
+            "new_str": "one\ntwo",
+        });
+        serde_json::from_value::<FsWrite>(v)
+            .unwrap()
+            .invoke(&os, &mut stdout, &mut line_tracker)
+            .await
+            .unwrap();
+
+        assert_eq!(os.fs.read_to_string(path).await.unwrap(), "one\r\ntwo\r\nthird");
+    }
+
     #[tokio::test]
     async fn test_fs_write_tool_insert_at_beginning() {
         let os = setup_test_directory().await;