diff --git a/src/AppDelegate.swift b/src/AppDelegate.swift
index 16f9e82..5b9f79f 100644
--- a/src/AppDelegate.swift
+++ b/src/AppDelegate.swift
@@ -186,13 +186,26 @@ class AppDelegate: NSObject, NSApplicationDelegate {
     @objc private func saveNoteAs() {
         let panel = NSSavePanel()
         panel.allowedContentTypes = [UTType(filenameExtension: "md")!]
-        panel.nameFieldStringValue = "note.md"
+        panel.nameFieldStringValue = defaultFilename()
         panel.beginSheetModal(for: window) { [weak self] response in
             guard response == .OK, let url = panel.url else { return }
             self?.appState.saveNoteToFile(url)
         }
     }
 
+    private func defaultFilename() -> String {
+        let firstLine = appState.documentText
+            .components(separatedBy: "\n").first?
+            .trimmingCharacters(in: .whitespaces) ?? ""
+        let stripped = firstLine.replacingOccurrences(
+            of: "^#+\\s*", with: "", options: .regularExpression
+        )
+        let trimmed = stripped.trimmingCharacters(in: .whitespaces)
+        guard !trimmed.isEmpty, trimmed != "Untitled" else { return "note.md" }
+        let sanitized = trimmed.map { "/:\\\\".contains($0) ? "-" : String($0) }.joined()
+        return sanitized.prefix(80) + ".md"
+    }
+
     @objc private func openSettings() {
         SettingsWindowController.show()
     }