projectdiscovery/subfinder ? reverse-engineered prompt

Build me a command-line tool for security reconnaissance, specifically for passive subdomain enumeration. I'm a bug bounty hunter and need a fast, lightweight tool written in Go.

Its main job is to take a domain name, or a list of domains from a file, and discover all its subdomains using a wide variety of public online sources. It needs to be smart about filtering out wildcards and bad results.

The tool should be able to output results as a simple list, save them to a file, or export as JSON so I can use it with other scripts. It's really important that I can also pipe domains into it and chain its output with other tools in my workflow. Also include options to filter the results and maybe choose or exclude certain data sources. Some of these sources might need API keys, so make sure there's a config file to handle that.