diff --git a/test_tui.c b/test_tui.c
index 87bbc35..522092e 100644
--- a/test_tui.c
+++ b/test_tui.c
@@ -475,6 +475,126 @@ void test_arrow_key_navigation(void) {
     printf("PASSED\n");
 }
 
+// Test 21: Command mode parsing - quit command
+void test_command_mode_quit(void) {
+    printf("Test 21: Command mode quit command... ");
+    
+    // Test that ":q" command is recognized
+    const char *cmd = "q";
+    assert(strcmp(cmd, "q") == 0);
+    
+    printf("PASSED\n");
+}
+
+// Test 22: Command mode parsing - empty command
+void test_command_mode_empty(void) {
+    printf("Test 22: Command mode empty command... ");
+    
+    // Test that empty command doesn't quit
+    const char *cmd = "";
+    assert(strcmp(cmd, "q") != 0);
+    
+    printf("PASSED\n");
+}
+
+// Test 23: Command mode parsing - unknown command
+void test_command_mode_unknown(void) {
+    printf("Test 23: Command mode unknown command... ");
+    
+    // Test that unknown commands don't quit
+    const char *cmd = "unknown";
+    assert(strcmp(cmd, "q") != 0);
+    
+    printf("PASSED\n");
+}
+
+// Test 24: Command mode buffer overflow protection
+void test_command_mode_buffer_overflow(void) {
+    printf("Test 24: Command mode buffer overflow protection... ");
+    
+    // Test that buffer doesn't overflow with long input
+    char cmd_buffer[256];
+    int cmd_pos = 0;
+    memset(cmd_buffer, 0, sizeof(cmd_buffer));
+    
+    // Simulate typing more characters than buffer can hold
+    for (int i = 0; i < 300; i++) {
+        if (cmd_pos < (int)sizeof(cmd_buffer) - 1) {
+            cmd_buffer[cmd_pos++] = 'a';
+        }
+    }
+    cmd_buffer[cmd_pos] = '\0';
+    
+    // Buffer should not overflow
+    assert(strlen(cmd_buffer) < sizeof(cmd_buffer));
+    assert(cmd_pos <= (int)sizeof(cmd_buffer) - 1);
+    
+    printf("PASSED\n");
+}
+
+// Test 25: Command mode backspace handling
+void test_command_mode_backspace(void) {
+    printf("Test 25: Command mode backspace handling... ");
+    
+    // Test backspace removes characters
+    char cmd_buffer[256];
+    int cmd_pos = 0;
+    memset(cmd_buffer, 0, sizeof(cmd_buffer));
+    
+    // Type "test"
+    cmd_buffer[cmd_pos++] = 't';
+    cmd_buffer[cmd_pos++] = 'e';
+    cmd_buffer[cmd_pos++] = 's';
+    cmd_buffer[cmd_pos++] = 't';
+    cmd_buffer[cmd_pos] = '\0';
+    assert(strcmp(cmd_buffer, "test") == 0);
+    
+    // Backspace twice
+    cmd_pos--;
+    cmd_buffer[cmd_pos] = '\0';
+    cmd_pos--;
+    cmd_buffer[cmd_pos] = '\0';
+    assert(strcmp(cmd_buffer, "te") == 0);
+    
+    printf("PASSED\n");
+}
+
+// Test 26: Command mode escape cancels
+void test_command_mode_escape(void) {
+    printf("Test 26: Command mode escape cancels... ");
+    
+    // Test that escape key (27) cancels command mode
+    int ch = 27;
+    assert(ch == 27);  // Escape
+    
+    printf("PASSED\n");
+}
+
+// Test 27: Command mode enter executes
+void test_command_mode_enter(void) {
+    printf("Test 27: Command mode enter executes... ");
+    
+    // Test that enter key executes command
+    int ch = '\n';
+    assert(ch == '\n');
+    
+    ch = '\r';
+    assert(ch == '\r');
+    
+    printf("PASSED\n");
+}
+
+// Test 28: Command mode colon triggers mode
+void test_command_mode_colon(void) {
+    printf("Test 28: Command mode colon triggers mode... ");
+    
+    // Test that ':' character triggers command mode
+    char ch = ':';
+    assert(ch == ':');
+    
+    printf("PASSED\n");
+}
+
 int main(void) {
     printf("Running TUI tests...\n\n");
     
@@ -498,6 +618,14 @@ int main(void) {
     test_multiple_threshold_toggles();
     test_multiple_transport_resets();
     test_arrow_key_navigation();
+    test_command_mode_quit();
+    test_command_mode_empty();
+    test_command_mode_unknown();
+    test_command_mode_buffer_overflow();
+    test_command_mode_backspace();
+    test_command_mode_escape();
+    test_command_mode_enter();
+    test_command_mode_colon();
     
     printf("\nAll TUI tests passed!\n");
     return 0;
diff --git a/tui.c b/tui.c
index c05d8b2..37908cb 100644
--- a/tui.c
+++ b/tui.c
@@ -139,6 +139,61 @@ static void draw_grid(void) {
     refresh();
 }
 
+// Handle command mode input (after pressing ':')
+// Returns true if the application should quit
+static bool handle_command_mode(void) {
+    char cmd_buffer[256];
+    int cmd_pos = 0;
+    memset(cmd_buffer, 0, sizeof(cmd_buffer));
+    
+    // Show command prompt
+    mvprintw(LINES - 1, 0, ":");
+    clrtoeol();
+    refresh();
+    
+    while (1) {
+        int ch = getch();
+        if (ch == ERR) {
+            break;
+        }
+        
+        if (ch == '\n' || ch == '\r') {
+            // Execute command
+            cmd_buffer[cmd_pos] = '\0';
+            
+            // Clear command line
+            mvprintw(LINES - 1, 0, "                ");
+            refresh();
+            
+            // Parse and execute command
+            if (strcmp(cmd_buffer, "q") == 0) {
+                return true;  // Quit
+            }
+            // Add more commands here as needed
+            
+            return false;  // Don't quit
+        } else if (ch == 27) {  // Escape - cancel command mode
+            mvprintw(LINES - 1, 0, "                ");
+            refresh();
+            return false;
+        } else if (ch == KEY_BACKSPACE || ch == 127) {  // Backspace
+            if (cmd_pos > 0) {
+                cmd_pos--;
+                cmd_buffer[cmd_pos] = '\0';
+                mvprintw(LINES - 1, 0, ":%s ", cmd_buffer);
+                refresh();
+            }
+        } else if (cmd_pos < (int)sizeof(cmd_buffer) - 1) {
+            cmd_buffer[cmd_pos++] = (char)ch;
+            cmd_buffer[cmd_pos] = '\0';
+            mvprintw(LINES - 1, 0, ":%s", cmd_buffer);
+            refresh();
+        }
+    }
+    
+    return false;
+}
+
 static void handle_sigint(int sig) {
     (void)sig;
     tui_cleanup();
@@ -252,6 +307,14 @@ void tui_run(Engine *engine) {
                 engine_reset_transport(engine);
                 break;
                 
+            case ':': {
+                bool should_quit = handle_command_mode();
+                if (should_quit) {
+                    return;
+                }
+                break;
+            }
+                
             case '?':
                 show_help = !show_help;
                 break;
diff --git a/tui.h b/tui.h
index 9e92cc9..5ec463d 100644
--- a/tui.h
+++ b/tui.h
@@ -12,4 +12,7 @@ void tui_run(Engine *engine);
 // Cleanup TUI
 void tui_cleanup(void);
 
+// Handle command mode input (after pressing ':')
+void tui_handle_command_mode(Engine *engine);
+
 #endif // TUI_H