Nuclei is a fast, customizable vulnerability scanner written in Go that uses a simple YAML-based domain-specific language to enable security professionals to create and share vulnerability detection templates. The tool is designed to find vulnerabilities across applications, APIs, networks, DNS, and cloud configurations by leveraging templates contributed by thousands of security researchers globally. The YAML-based approach allows users to define custom vulnerability detection scenarios that mimic real-world conditions, which the project claims leads to zero false positives by simulating actual attack steps rather than relying on simple pattern matching.

The scanner supports multiple protocols including TCP, DNS, HTTP, SSL, WHOIS, JavaScript, and Code, enabling comprehensive security testing across diverse infrastructure types. Nuclei can perform single target scans, bulk scanning of multiple targets from files, and network-wide scanning for issues like open ports and misconfigured services. The tool integrates into CI/CD pipelines for continuous vulnerability detection and regression testing, and supports integration with platforms like Jira, Splunk, GitHub, Elastic, and GitLab for streamlined vulnerability management and reporting.

According to GitGenius activity tracking, the repository shows significant community engagement with 1043 tracked issues and pull requests. The most active contributors include dogancanbakir with 830 events, dwisiswant0 with 693 events, and Mzack9999 with 482 events. The issue tracker reveals that Type: Bug reports are the most common category with 553 items, followed by Type: Enhancement requests with 311 items, indicating active bug fixing and feature development. The median response latency for issues and pull requests is 0.0 hours, though the mean latency of 3940.9 hours reflects the natural variation in response times across the large volume of submissions.

The project maintains a separate nuclei-templates repository containing the community-contributed detection templates that power the scanner. The README indicates support for multiple languages including English, Chinese, Korean, Indonesian, Spanish, Japanese, Portuguese, and Turkish, reflecting the tool's global user base. The project offers both open-source and commercial editions, with Pro and Enterprise versions providing cloud-hosted scanning at scale, integrations with cloud services like AWS, GCP, and Azure, and additional features such as real-time scanning and SAML SSO.

Nuclei emphasizes ultra-fast parallel scan processing and request clustering to handle large-scale vulnerability assessments efficiently. The project includes a free cloud tier with generous monthly limits for storing findings, writing templates, accessing the latest template library, and discovering targets. The repository is actively maintained with breaking changes expected between releases, and the project explicitly notes that running Nuclei as a service may pose security risks and recommends using it primarily as a standalone CLI tool with appropriate security measures.