diff --git a/crates/ruff_server/src/message.rs b/crates/ruff_server/src/message.rs
index 79d7c63ec347a..ef692e3561488 100644
--- a/crates/ruff_server/src/message.rs
+++ b/crates/ruff_server/src/message.rs
@@ -37,10 +37,18 @@ pub(super) fn try_show_message(
     Ok(())
 }
 
-/// Sends an error to the client with a formatted message. The error is sent in a
-/// `window/showMessage` notification.
+/// Sends a request to display an error to the client with a formatted message. The error is sent
+/// in a `window/showMessage` notification.
 macro_rules! show_err_msg {
     ($msg:expr$(, $($arg:tt),*)?) => {
         crate::message::show_message(::core::format_args!($msg, $($($arg),*)?).to_string(), lsp_types::MessageType::ERROR)
     };
 }
+
+/// Sends a request to display a warning to the client with a formatted message. The warning is
+/// sent in a `window/showMessage` notification.
+macro_rules! show_warn_msg {
+    ($msg:expr$(, $($arg:tt),*)?) => {
+        crate::message::show_message(::core::format_args!($msg, $($($arg),*)?).to_string(), lsp_types::MessageType::WARNING)
+    };
+}
diff --git a/crates/ruff_server/src/session/index.rs b/crates/ruff_server/src/session/index.rs
index feace554a5445..cca313d817605 100644
--- a/crates/ruff_server/src/session/index.rs
+++ b/crates/ruff_server/src/session/index.rs
@@ -200,16 +200,21 @@ impl Index {
         workspace_settings: Option<ClientSettings>,
         global_settings: &ClientSettings,
     ) -> crate::Result<()> {
+        if workspace_url.scheme() != "file" {
+            tracing::warn!("Ignoring non-file workspace: {workspace_url}");
+            show_warn_msg!("Ruff does not support non-file workspaces; Ignoring {workspace_url}");
+            return Ok(());
+        }
+        let workspace_path = workspace_url.to_file_path().map_err(|()| {
+            anyhow!("Failed to convert workspace URL to file path: {workspace_url}")
+        })?;
+
         let client_settings = if let Some(workspace_settings) = workspace_settings {
             ResolvedClientSettings::with_workspace(&workspace_settings, global_settings)
         } else {
             ResolvedClientSettings::global(global_settings)
         };
 
-        let workspace_path = workspace_url
-            .to_file_path()
-            .map_err(|()| anyhow!("workspace URL was not a file path!"))?;
-
         let workspace_settings_index = ruff_settings::RuffSettingsIndex::new(
             &workspace_path,
             client_settings.editor_settings(),
@@ -227,9 +232,9 @@ impl Index {
     }
 
     pub(super) fn close_workspace_folder(&mut self, workspace_url: &Url) -> crate::Result<()> {
-        let workspace_path = workspace_url
-            .to_file_path()
-            .map_err(|()| anyhow!("workspace URL was not a file path!"))?;
+        let workspace_path = workspace_url.to_file_path().map_err(|()| {
+            anyhow!("Failed to convert workspace URL to file path: {workspace_url}")
+        })?;
 
         self.settings.remove(&workspace_path).ok_or_else(|| {
             anyhow!(