# agent_appkit The macOS GUI backend for the [agent surface](/docs/agent-surface): it binds the framework-agnostic [agent_core](/docs/packages/agent_core) rules to a live [AppKit](/docs/packages/appkit) window. - **`open(window)`** walks the live NSView tree into a `Surface` — the controllable model an agent sees. - **`describe_ui`** returns a snapshot of the exposed nodes (`Vec[UiNode]`). A node is exposed by giving it an agent id with `set_agent_id`. - **Authorized actions** — `click`, `set_text`, and `scroll_to` run through the `agent_core` authorization brain. Text edits use optimistic-concurrency versioning, so a stale edit is rejected. - **Events** — AppKit notifications are translated into verbs and delivered as the bubbling events `agent_core` defines. - **Main-thread safe** — `click` / `set_text` / `scroll_to` marshal onto the main thread when called off it, so an MCP bridge driven on a background connection can never message AppKit off-main. It is closure-free (a `[NSThread isMainThread]` fast path over `performSelectorOnMainThread:`), and `on_main_thread()` is public if you need the same check. - **Layout diagnostics** — `Surface::layout_diagnostics` reports per-node Auto Layout health (`uses_autolayout`, `has_ambiguous_layout`), so an agent can catch a broken generated layout without taking a screenshot. Pair it with [agent_mcp](/docs/packages/agent_mcp) to expose the surface to an external agent. [AppKit agent surface](/examples/appkit-agent-counter) documents the checked `docs/examples/recipes/appkit_agent` recipe from the C+ source tree: describe the tagged UI, act on a real AppKit button, reject stale text edits, and refuse requests through a closed consent gate.