diff --git a/toki-tui/src/api/dev_backend.rs b/toki-tui/src/api/dev_backend.rs
index 1a586aa3..28a90a57 100644
--- a/toki-tui/src/api/dev_backend.rs
+++ b/toki-tui/src/api/dev_backend.rs
@@ -49,6 +49,7 @@ impl DevBackend {
                 start_time: Some(e.start_time),
                 end_time: e.end_time,
                 week_number: e.start_time.iso_week(),
+                attest_level: Default::default(),
             })
             .collect()
     }
diff --git a/toki-tui/src/app/edit.rs b/toki-tui/src/app/edit.rs
index 93b5f9fd..2733bef6 100644
--- a/toki-tui/src/app/edit.rs
+++ b/toki-tui/src/app/edit.rs
@@ -1,5 +1,8 @@
 use super::*;
 
+const LOCKED_ENTRY_MSG: &str = "Entry is locked and cannot be edited";
+const LOCKED_DELETE_MSG: &str = "Entry is locked and cannot be deleted";
+
 impl App {
     /// Enter edit mode for the currently focused This Week entry
     pub fn enter_this_week_edit_mode(&mut self) {
@@ -27,6 +30,13 @@ impl App {
                 } else {
                     idx
                 };
+                // Guard: locked entries cannot be edited
+                if let Some(entry) = self.this_week_history().get(db_idx) {
+                    if entry.attest_level.is_locked() {
+                        self.set_status(LOCKED_ENTRY_MSG.to_string());
+                        return;
+                    }
+                }
                 let entry_data = self.this_week_history().get(db_idx).map(|e| {
                     let (start_time, end_time) =
                         derive_start_end(e.start_time, e.end_time, &e.date, e.hours);
@@ -72,6 +82,13 @@ impl App {
     pub fn enter_history_edit_mode(&mut self) {
         if let Some(list_idx) = self.focused_history_index {
             if let Some(&history_idx) = self.history_list_entries.get(list_idx) {
+                // Guard: locked entries cannot be edited
+                if let Some(entry) = self.time_entries.get(history_idx) {
+                    if entry.attest_level.is_locked() {
+                        self.set_status(LOCKED_ENTRY_MSG.to_string());
+                        return;
+                    }
+                }
                 let entry_data = self.time_entries.get(history_idx).map(|e| {
                     let (start_time, end_time) =
                         derive_start_end(e.start_time, e.end_time, &e.date, e.hours);
@@ -566,6 +583,37 @@ impl App {
         }
     }
 
+    /// Returns true if the currently focused history entry is locked.
+    pub fn focused_history_entry_is_locked(&self) -> bool {
+        self.focused_history_index
+            .and_then(|list_idx| self.history_list_entries.get(list_idx))
+            .and_then(|&history_idx| self.time_entries.get(history_idx))
+            .map(|e| e.attest_level.is_locked())
+            .unwrap_or(false)
+    }
+
+    /// Returns true if the currently focused This Week entry is locked.
+    pub fn focused_this_week_entry_is_locked(&self) -> bool {
+        self.focused_this_week_index
+            .map(|idx| {
+                let db_idx = if self.timer_state == TimerState::Running {
+                    idx.saturating_sub(1)
+                } else {
+                    idx
+                };
+                self.this_week_history()
+                    .get(db_idx)
+                    .map(|e| e.attest_level.is_locked())
+                    .unwrap_or(false)
+            })
+            .unwrap_or(false)
+    }
+
+    /// Set the status message for a locked-entry delete attempt.
+    pub fn set_locked_delete_status(&mut self) {
+        self.set_status(LOCKED_DELETE_MSG.to_string());
+    }
+
     /// Check if we're in any edit mode
     pub fn is_in_edit_mode(&self) -> bool {
         self.this_week_edit_state.is_some() || self.history_edit_state.is_some()
diff --git a/toki-tui/src/runtime/views/history.rs b/toki-tui/src/runtime/views/history.rs
index ffa0b4a6..5f49f955 100644
--- a/toki-tui/src/runtime/views/history.rs
+++ b/toki-tui/src/runtime/views/history.rs
@@ -110,13 +110,21 @@ pub(super) fn handle_history_key(key: KeyEvent, app: &mut App, action_tx: &Actio
             }
             KeyCode::Char('q') | KeyCode::Char('Q') => app.quit(),
             KeyCode::Delete | KeyCode::Backspace if app.focused_history_index.is_some() => {
-                app.enter_delete_confirm(app::DeleteOrigin::History);
+                if app.focused_history_entry_is_locked() {
+                    app.set_locked_delete_status();
+                } else {
+                    app.enter_delete_confirm(app::DeleteOrigin::History);
+                }
             }
             KeyCode::Char('x')
                 if key.modifiers.contains(KeyModifiers::CONTROL)
                     && app.focused_history_index.is_some() =>
             {
-                app.enter_delete_confirm(app::DeleteOrigin::History);
+                if app.focused_history_entry_is_locked() {
+                    app.set_locked_delete_status();
+                } else {
+                    app.enter_delete_confirm(app::DeleteOrigin::History);
+                }
             }
             _ => {}
         }
diff --git a/toki-tui/src/runtime/views/timer.rs b/toki-tui/src/runtime/views/timer.rs
index 6b0186ae..9e9ebd04 100644
--- a/toki-tui/src/runtime/views/timer.rs
+++ b/toki-tui/src/runtime/views/timer.rs
@@ -95,7 +95,11 @@ pub(super) fn handle_timer_key(key: KeyEvent, app: &mut App, action_tx: &ActionT
                     app.entry_edit_backspace();
                 }
             } else if is_persisted_today_row_selected(app) {
-                app.enter_delete_confirm(app::DeleteOrigin::Timer);
+                if app.focused_this_week_entry_is_locked() {
+                    app.set_locked_delete_status();
+                } else {
+                    app.enter_delete_confirm(app::DeleteOrigin::Timer);
+                }
             }
         }
         KeyCode::Esc => {
@@ -123,7 +127,11 @@ pub(super) fn handle_timer_key(key: KeyEvent, app: &mut App, action_tx: &ActionT
             handle_ctrl_x_key(app, action_tx);
         }
         KeyCode::Delete if !is_editing_this_week(app) && is_persisted_today_row_selected(app) => {
-            app.enter_delete_confirm(app::DeleteOrigin::Timer);
+            if app.focused_this_week_entry_is_locked() {
+                app.set_locked_delete_status();
+            } else {
+                app.enter_delete_confirm(app::DeleteOrigin::Timer);
+            }
         }
         KeyCode::Char('z') | KeyCode::Char('Z') => app.toggle_zen_mode(),
         _ => {}
@@ -233,7 +241,11 @@ fn handle_ctrl_x_key(app: &mut App, action_tx: &ActionTx) {
     }
 
     if is_persisted_today_row_selected(app) {
-        app.enter_delete_confirm(app::DeleteOrigin::Timer);
+        if app.focused_this_week_entry_is_locked() {
+            app.set_locked_delete_status();
+        } else {
+            app.enter_delete_confirm(app::DeleteOrigin::Timer);
+        }
         return;
     }
 
diff --git a/toki-tui/src/types.rs b/toki-tui/src/types.rs
index f9cd15e0..b075f008 100644
--- a/toki-tui/src/types.rs
+++ b/toki-tui/src/types.rs
@@ -16,6 +16,32 @@ pub struct Activity {
     pub project_id: String,
 }
 
+/// Attestation / lock level for a time entry, matching the Milltime API value.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, serde::Deserialize)]
+#[serde(from = "u8")]
+pub enum AttestLevel {
+    #[default]
+    None = 0,
+    Week = 1,
+    Month = 2,
+}
+
+impl From<u8> for AttestLevel {
+    fn from(v: u8) -> Self {
+        match v {
+            1 => AttestLevel::Week,
+            2 => AttestLevel::Month,
+            _ => AttestLevel::None,
+        }
+    }
+}
+
+impl AttestLevel {
+    pub fn is_locked(self) -> bool {
+        self != AttestLevel::None
+    }
+}
+
 /// A completed time entry from Milltime (via GET /time-tracking/time-entries).
 /// start_time / end_time are optional — present only if a local timer history record exists.
 #[derive(Debug, Clone, Deserialize)]
@@ -36,6 +62,8 @@ pub struct TimeEntry {
     pub end_time: Option<OffsetDateTime>,
     #[allow(dead_code)]
     pub week_number: u8,
+    #[serde(default)]
+    pub attest_level: AttestLevel,
 }
 
 /// The current user, as returned by GET /me.
diff --git a/toki-tui/src/ui/widgets.rs b/toki-tui/src/ui/widgets.rs
index f1b33374..d6d61a4c 100644
--- a/toki-tui/src/ui/widgets.rs
+++ b/toki-tui/src/ui/widgets.rs
@@ -73,10 +73,9 @@ pub fn build_display_row(
     is_overlapping: bool,
     available_width: u16,
 ) -> Line<'_> {
-    // Warning emoji for overlapping entries
-    let warning_prefix = if is_overlapping { "⚠ " } else { "" };
+    let is_locked = entry.attest_level.is_locked();
 
-    // Base colors - red for overlapping, normal for non-overlapping
+    // Base colors - red for overlapping, normal otherwise (locked entries keep normal colors)
     let time_color = if is_overlapping {
         Color::Red
     } else {
@@ -132,8 +131,9 @@ pub fn build_display_row(
 
     // Responsive truncation: compute remaining width after fixed prefix.
     // Non-overlapping: "HH:MM - HH:MM " (14) + "[DDh:DDm]" (9) + " | " (3) = 26
-    // Overlapping adds "⚠ " (2 chars: symbol + space) = 28
-    let prefix_len: usize = if is_overlapping { 28 } else { 26 };
+    // Both ⊘ and ⚠ are 2 chars (symbol + space), so same budget = 28
+    let has_prefix = is_locked || is_overlapping;
+    let prefix_len: usize = if has_prefix { 28 } else { 26 };
     let remaining = (available_width as usize).saturating_sub(prefix_len);
 
     let proj_act = format!("{}: {}", project, activity);
@@ -142,12 +142,12 @@ pub fn build_display_row(
     // Build styled line with colors
     let mut spans = vec![];
 
-    // Warning prefix for overlapping entries
-    if is_overlapping {
-        spans.push(Span::styled(
-            warning_prefix,
-            Style::default().fg(Color::Red),
-        ));
+    // Locked takes visual precedence over overlap — attested entries cannot be
+    // edited regardless of overlap, so the lock indicator is more actionable.
+    if is_locked {
+        spans.push(Span::styled("⊘ ", Style::default().fg(Color::Red)));
+    } else if is_overlapping {
+        spans.push(Span::styled("⚠ ", Style::default().fg(Color::Red)));
     }
 
     // Show time range — use real times if available, otherwise a dimmed placeholder