diff --git a/tuner/tuner/candidate_gen.py b/tuner/tuner/candidate_gen.py
index 51c2d5114..e7a83a507 100644
--- a/tuner/tuner/candidate_gen.py
+++ b/tuner/tuner/candidate_gen.py
@@ -290,7 +290,7 @@ def strip_compilation_info(input_path: Path) -> str:
     return result.process_res.stdout
 
 
-def main():
+def main() -> None:
     parser = argparse.ArgumentParser()
     parser.add_argument("input", help="Input mlir file", type=str)
     parser.add_argument(
@@ -349,7 +349,7 @@ def main():
             prefetch_shared_memory=args.prefetch_shared_memory_options,
             no_reduce_shared_memory_bank_conflicts=args.no_reduce_shared_memory_bank_conflicts_options,
         )
-        specs = generate_configs_and_td_specs(
+        specs: list[ir.Module] = generate_configs_and_td_specs(
             mlir_module,
             tuner_ctx,
             args.limit,
@@ -363,9 +363,9 @@ def main():
             spec_path = spec_dir / f"{candidate_num}_spec.mlir"
             spec_dir.mkdir(parents=True, exist_ok=True)
             with open(spec_path, "w") as f:
-                local_scope_spec_str = spec.operation.get_asm(use_local_scope=True)
+                local_scope_spec_str: str = spec.operation.get_asm(use_local_scope=True)
                 f.write(local_scope_spec_str)
 
 
 if __name__ == "__main__":
-    args = main()
+    main()