Nuclei is an open-source scanning engine that can be used to detect security vulnerabilities, misconfigurations, and exposed services across web applications, infrastructure, cloud environments, and networks. It requires Go version 1.21 or higher to install and can be installed using the `go install -v` command. Nuclei templates are structured in YAML Ain't Markup Language (YAML) and provide a human-readable syntax for defining requests and parsing responses. The tool provides a Domain Specific Language (DSL) for writing complex expressions, making it powerful and easy to read. Templates can be used to systematically replicate discoveries across targets en masse. Nuclei has an active community of hackers and regular maintenance, ensuring that templates stay up-to-date with the latest exploits and attack vectors. The tool allows users to view available templates, filter output, select specific templates, and generate Markdown reports. It also provides out-of-band testing capabilities through integration with ProjectDiscovery's Interactsh tool. Users can create custom templates using YAML and DSL syntax, allowing them to harness the full potential of Nuclei. With its extensibility and customizable nature, Nuclei is a valuable asset for bug bounty hunters and security professionals.