Subfinder

Fast, passive subdomain discovery tool written in Go that uses certificate transparency logs, search engines, and DNS data sources.

OSINT Passive Discovery Fast Enumeration Bug Bounty

Overview

Subfinder is a fast, reliable subdomain discovery tool built in Go. It operates passively, collecting subdomains from certificate transparency logs, search engines, and various DNS data sources without directly interacting with target systems. Key features include high performance, multiple data source integration, JSON output support, and compatibility with other bug bounty tools. Subfinder is widely used in penetration testing, bug bounty hunting, and asset discovery.

Primary Use Cases

✔ Discovering subdomains and attack surfaces during penetration testing and bug bounty hunting.

✔ Performing asset discovery through passive data collection from certificate transparency logs.

✔ Conducting initial reconnaissance for security assessments and vulnerability research.

Frequently Asked Questions

Subfinder is a fast, passive subdomain discovery tool created by ProjectDiscovery. It's written in Go and collects subdomains from certificate transparency logs and public data sources.

Yes, Subfinder is completely free and open-source under the MIT license. It's maintained by the ProjectDiscovery community.

Subfinder focuses on fast, passive subdomain discovery using certificate logs and data sources, while Amass offers a broader range of techniques including active enumeration. Both complement each other in reconnaissance workflows.

Subfinder uses certificate transparency logs, search engines, DNS data sources, and various public APIs to discover subdomains passively.

Subfinder supports multiple output formats including JSON, CSV, and plain text, making it compatible with other security tools and automation workflows.

Metadata

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Category Info

Open Source Intelligence (OSINT) tools for gathering and analyzing publicly available information from various sources including websites, social media, DNS records, public databases, and other open data sources for security investigations and threat intelligence.

Added On

August 18, 2026

Last Updated

August 18, 2026