Which AWS tool or feature acts as a VPC firewall at the subnet level?

Network ACLs (NACLs) are subnet-level firewalls in AWS, controlling inbound and outbound traffic for VPC subnets. They provide an additional layer of security by allowing or denying traffic based on IP protocol, source and destination IP, and port. Security groups operate at the instance level, while Traffic Mirroring and Internet Gateways do not function as firewalls at the subnet level.