egui_inspection

Inspection for egui apps.

egui_inspection defines a wire protocol and an [egui::Plugin] (InspectionPlugin) that serves it. An external inspector — such as the egui_mcp MCP server — connects and can:

• read the app's AccessKit tree (GetTree),
• inject input events (HandleEvents — clicks, typing, scrolling, …),
• capture a screenshot on request (Screenshot),
• resize the window (Resize).

The protocol is strictly request → response, which maps cleanly onto both a TCP socket and a unary RPC (so the same machinery can be tunnelled over another transport).

Screenshots need a visible window. Reading the tree and injecting input work even while the app is in the background, but capturing a screenshot requires a rendered frame — which the OS won't produce for a fully-occluded or minimized window (notably on macOS, where the GPU surface isn't available). Bring the window to the foreground to capture it; the Screenshot request times out otherwise.

What it's for

egui_inspection is the shared foundation for tools that observe or drive an egui app from the outside. Anything that speaks the protocol (over TCP, or another transport) can be a consumer:

• egui_mcp — an MCP server that exposes the app to AI agents and other tooling: query the widget tree, click / type / scroll, take screenshots.
• An egui inspector GUI (planned) — a visual debugger that connects to a running app to browse its widget tree and drive it interactively.
• Test inspection & frame streaming (planned) — attach to egui_kittest tests, and stream frames for live mirroring of an app's window.

Enabling it in an eframe app

Enable eframe's inspection feature, then set the EGUI_INSPECTION env var at runtime. It's either truthy, falsy, or a bind address:

EGUI_INSPECTION=1 cargo run --features inspection            # binds 127.0.0.1:5719
EGUI_INSPECTION=0.0.0.0:5719 cargo run --features inspection # reachable across devices

When the variable is unset or falsy (0 / false), inspection is completely off (production-safe).

⚠️ Binding a non-loopback address exposes full control of the app — and its screenshots — to anyone who can reach the port, with no authentication. A warning is logged when you do so. Prefer loopback + an SSH tunnel for remote debugging.

Using the plugin directly

# let ctx = egui::Context::default();
ctx.add_plugin(egui_inspection::InspectionPlugin::new(Some("my app".to_owned())));
egui_inspection::serve(&ctx, "127.0.0.1:5719").unwrap();