SigmaQuery is a comprehensive online repository and search platform for Sigma detection rules maintained by Nextron Systems. The platform provides access to over 3,000 detection rules designed to identify malicious activity across various platforms including Windows, Linux, macOS, cloud environments (AWS, Azure, GCP), and network infrastructure. The rules are categorized by severity levels (Critical, High, Medium, Low, Informational) and maturity status (Stable, Test, Experimental), with extensive coverage of the MITRE ATT&CK framework spanning 385+ techniques. Each rule includes metadata such as author information, creation date, and targeted products. The platform enables security analysts and threat hunters to search, filter, and browse detection rules by multiple criteria including MITRE ATT&CK technique, severity level, product platform, and rule status. Rules cover diverse threat scenarios from credential dumping and lateral movement to persistence mechanisms and defense evasion techniques. The repository includes detection logic for specific threats like the Microsoft Malware Protection Engine crash, LSASS process crashes, suspicious process behaviors, and various attack techniques across operating systems and cloud platforms. SigmaQuery serves as a centralized resource for security operations teams to implement detection capabilities across their SIEM and security monitoring infrastructure.