# agent_gtk `agent_gtk` walks a live GTK 4 widget hierarchy into [agent_core](/docs/packages/agent_core). It classifies widgets through their GObject ancestry, reads their current geometry and content, and implements the same grant-aware backend used on the other platforms. ```cplus import "agent_gtk/agent_gtk" as agent; import "agent_core/auth" as auth; agent::set_agent_id(button.raw(), #str_ptr("save\0")); var surface = agent::open(window.raw()); let nodes = surface.describe(auth::reader()); let result = surface.click(auth::operator(), "save"); ``` `set_agent_policy` pins Protected, Private, or excluded content to a widget. `mcp_backend()` supplies the platform-neutral vtable for `agent_mcp` and `agent_inapp`. Actions include live-tree refresh, exposure and affordance checks, capability grants, versioned text writes, and semantic event delivery. GTK remains single-threaded; callers running the backend away from the GTK main thread must marshal according to the same rule as other GTK code. Facet applications normally use [facet_agent](/docs/packages/facet_agent), which selects this backend on Linux.