diff --git a/agentrace/cli.py b/agentrace/cli.py
index fec377b..36d6753 100644
--- a/agentrace/cli.py
+++ b/agentrace/cli.py
@@ -101,6 +101,9 @@ def cmd_check(args) -> int:
 
 def cmd_show(args) -> int:
     runs = _load(args)
+    if args.id == "":
+        console.print("[red]Please provide a run ID[/]", file=sys.stderr)
+        return 1
     match = [r for r in runs if r.tool_use_id.endswith(args.id)]
     if not match:
         console.print(f"[red]No run matching {args.id!r}[/]")
diff --git a/tests/test_cli.py b/tests/test_cli.py
index ba17ee4..304af54 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -108,6 +108,14 @@ def test_empty_result_names_selected_file(tmp_path):
     assert result.returncode == 0
     assert "No subagent runs found." in result.stdout
     assert f"Looked in {transcript}." in result.stdout
+    
+def test_show_empty_id_errors(tmp_path):
+    transcript = tmp_path / "empty.jsonl"
+    transcript.write_text("")
+    result = run_cli("--file", str(transcript), "show", "")
+
+    assert result.returncode == 1
+    assert "Please provide a run ID" in result.stderr
 
 
 def test_empty_result_names_selected_directory(tmp_path):