When authoring a custom plugin for Copilot for Security that queries security telemetry and returns structured results, the expected query/target format is Kusto Query Language (KQL). Copilot for Security integrates with Microsoft security data platforms (Microsoft Sentinel/Log Analytics and Defender tables) where investigative and hunting queries are expressed in KQL. Official plugin examples and guidance show the plugin invoking a KQL query against a workspace or a Defender table and returning the results in the plugin response payload. KQL is the language used to interrogate event, alert, and entity tables (for example, DeviceProcessEvents, SecurityAlert, MicrosoftGraphActivityLogs) and is the supported format when a plugin's purpose is to retrieve and return telemetry to Copilot for Security. Other formats listed (API, GPT, SQL) are not the standard query language for Defender/Sentinel data: APIs are endpoints for programmatic access, GPT is a model format, and SQL is not used for Azure Monitor / Sentinel tables. Therefore when the plugin's <target> must specify the query format against security telemetry, KQL is the correct choice.