How should custom error codes be structured for clarity and scalability?

A common and effective structure for custom error codes involves segmenting them. For example, a prefix could indicate the module or service (e.g., 'AUTH' for authentication), followed by a category (e.g., '001' for invalid credentials), and then a specific instance of that error (e.g., '001-01'). This hierarchical approach aids in organization and scalability as the system grows.