subfinder README

Fast passive subdomain enumeration tool.

Features • Install • Usage • API Setup • Library • Join Discord

subfinder is a subdomain discovery tool that returns valid subdomains for websites, using passive online sources. It has a simple, modular architecture and is optimized for speed. subfinder is built for doing one thing only - passive subdomain enumeration, and it does that very well.

We have made it to comply with all the used passive source licenses and usage restrictions. The passive model guarantees speed and stealthiness that can be leveraged by both penetration testers and bug bounty hunters alike.

Features

Fast and powerful resolution and wildcard elimination modules
Curated passive sources to maximize results
Multiple output formats supported (JSON, file, stdout)
Optimized for speed and lightweight on resources
STDIN/OUT support enables easy integration into workflows

Usage

subfinder -h

This will display help for the tool. Here are all the switches it supports.

Usage:
  ./subfinder [flags]

Flags:
INPUT:
  -d, -domain string[]  domains to find subdomains for
  -dL, -list string     file containing list of domains for subdomain discovery

SOURCE:
  -s, -sources string[]           specific sources to use for discovery (-s crtsh,github). Use -ls to display all available sources.
  -recursive                      use only sources that can handle subdomains recursively (e.g. subdomain.domain.tld vs domain.tld)
  -all                            use all sources for enumeration (slow)
  -es, -exclude-sources string[]  sources to exclude from enumeration (-es alienvault,zoomeyeapi)

FILTER:
  -m, -match string[]   subdomain or list of subdomain to match (file or comma separated)
  -f, -filter string[]   subdomain or list of subdomain to filter (file or comma separated)

RATE-LIMIT:
  -rl, -rate-limit int  maximum number of http requests to send per second
  -rls value            maximum number of http requests to send per second for providers in key=value format (-rls "hackertarget=10/s,shodan=15/s")
  -t int                number of concurrent goroutines for resolving (-active only) (default 10)

UPDATE:
  -up, -update                 update subfinder to latest version
  -duc, -disable-update-check  disable automatic subfinder update check

OUTPUT:
  -o, -output string       file to write output to
  -oJ, -json               write output in JSONL(ines) format
  -oD, -output-dir string  directory to write output (-dL only)
  -cs, -collect-sources    include all sources in the output (-json only)
  -oI, -ip                 include host IP in output (-active only)

CONFIGURATION:
  -config string                flag config file (default "$CONFIG/subfinder/config.yaml")
  -pc, -provider-config string  provider config file (default "$CONFIG/subfinder/provider-config.yaml")
  -r string[]                   comma separated list of resolvers to use
  -rL, -rlist string            file containing list of resolvers to use
  -nW, -active                  display active subdomains only
  -proxy string                 http proxy to use with subfinder
  -ei, -exclude-ip              exclude IPs from the list of domains
  -mr, -max-results int         limit the number of results per source (0 = unlimited; honored by paginating sources)

DEBUG:
  -silent             show only subdomains in output
  -version            show version of subfinder
  -v                  show verbose output
  -nc, -no-color      disable color in output
  -ls, -list-sources  list all available sources (-oJ for JSON)

OPTIMIZATION:
  -timeout int                  seconds to wait before timing out (default 30)
  -max-time int                 minutes to wait for enumeration results (default 10)
  -rsr, -response-size-read int max response body size to read in bytes from passive sources (0 = unlimited)

Environment Variables

Subfinder supports environment variables to specify custom paths for configuration files:

SUBFINDER_CONFIG - Path to config.yaml file (overrides default $CONFIG/subfinder/config.yaml)
SUBFINDER_PROVIDER_CONFIG - Path to provider-config.yaml file (overrides default $CONFIG/subfinder/provider-config.yaml)

Installation

subfinder requires go1.24 to install successfully. Run the following command to install the latest version:

go install -v github.com/projectdiscovery/subfinder/v2/cmd/subfinder@latest

Learn about more ways to install subfinder here: https://docs.projectdiscovery.io/tools/subfinder/install.

Post Installation Instructions

subfinder can be used right after the installation, however many sources required API keys to work. Learn more here: https://docs.projectdiscovery.io/tools/subfinder/install#post-install-configuration.

Running Subfinder

Learn about how to run Subfinder here: https://docs.projectdiscovery.io/tools/subfinder/running.

Subfinder Go library

Subfinder can also be used as library and a minimal examples of using subfinder SDK is available here

Resources

Recon with Me !!!

License

subfinder is made with 🖤 by the projectdiscovery team. Community contributions have made the project what it is. See the THANKS.md file for more details.

Read the usage disclaimer at DISCLAIMER.md and contact us for any API removal.

14.6K ·GitHub

Subfinder

What is this?

Subfinder is a fast passive subdomain enumeration tool that returns valid subdomains for a website by querying passive online sources, built for penetration testers and bug bounty hunters.

Is this just a CLI tool, or can I use it as a library too?

It is primarily a CLI tool, but it also ships as a Go library (SDK) that you can import directly into your own Go programs for subdomain enumeration.

Do I need API keys to use it?

You can run Subfinder right after installing it, but many of its passive sources require API keys to actually return results, configured via a provider-config.yaml file.

Does it do active scanning or brute-forcing?

No, it is strictly passive — it only queries curated passive sources and does not perform active probing, which keeps it fast and stealthy but limits results to what those sources expose.

Who is this tool mainly built for?

It targets penetration testers and bug bounty hunters who need fast, stealthy subdomain discovery as part of their reconnaissance workflow.

Can I run this on any OS?

Yes, since it's a Go binary it runs cross-platform on Linux, macOS, and Windows.

Does it respect the licensing terms of the sources it queries?

Yes, the project is designed to comply with the usage restrictions and licenses of all the passive data sources it integrates with.

What output formats does it support?

Subfinder supports multiple output formats including JSON, file output, and stdout, and it works well with STDIN/STDOUT for piping into other tools.

Can I customize where config files live?

Yes, you can override the default config and provider-config paths using the SUBFINDER_CONFIG and SUBFINDER_PROVIDER_CONFIG environment variables.

Is there a Docker image available?

Yes, the project provides Docker support so you can run Subfinder in a container without installing Go locally.

What are similar projects?

bbot, httpx, OneForAll, awesome-hacker-search-engines, gobuster, ffuf, theHarvester, redamon

Which topics is it in?

subdomain-enumeration, bugbounty, reconnaissance, osint, penetration-testing, hacking, cybersecurity, hacktoberfest, go, security, terminal, library

Creator: projectdiscovery
Size: 10.1 MB
Stars: 14.6K
Updated: CommitOct 08 Releasev2.17.0Oct 08
Age: 8y
Commits · 90 Days