diff --git a/Cargo.lock b/Cargo.lock
index dfdde30e7..a39620f96 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -995,10 +995,21 @@ dependencies = [
  "zip 9.1.0",
 ]
 
+[[package]]
+name = "craft-web-api"
+version = "0.1.0"
+source = "git+https://github.com/storytold/craft-libs?rev=fd5e2feff6ea25bed371a99cc732b3968d621505#fd5e2feff6ea25bed371a99cc732b3968d621505"
+dependencies = [
+ "js-sys",
+ "serde_json",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+]
+
 [[package]]
 name = "craft-web-host"
 version = "0.1.0"
-source = "git+https://github.com/storytold/craft-libs?rev=2e2312ddaf21bc3d85cd3395d0955c7d239306f6#2e2312ddaf21bc3d85cd3395d0955c7d239306f6"
+source = "git+https://github.com/storytold/craft-libs?rev=fd5e2feff6ea25bed371a99cc732b3968d621505#fd5e2feff6ea25bed371a99cc732b3968d621505"
 dependencies = [
  "wasm-bindgen",
  "web-sys",
@@ -2195,6 +2206,7 @@ dependencies = [
 name = "gridcraft-web"
 version = "0.16.0"
 dependencies = [
+ "craft-web-api",
  "craft-web-host",
  "eframe",
  "egui",
diff --git a/apps/gridcraft-web/Cargo.toml b/apps/gridcraft-web/Cargo.toml
index e5c599bd8..09c6d7e2a 100644
--- a/apps/gridcraft-web/Cargo.toml
+++ b/apps/gridcraft-web/Cargo.toml
@@ -17,7 +17,9 @@ path = "src/main.rs"
 gridcraft-engine = { workspace = true }
 gridcraft-ui-egui = { workspace = true }
 # The host messages (storytold/craft-libs): one contract and one bridge for the web builds.
-craft-web-host = { git = "https://github.com/storytold/craft-libs", rev = "2e2312ddaf21bc3d85cd3395d0955c7d239306f6", version = "0.1.0" }
+# The page command API (storytold/craft-libs#413): window.gridcraft over the control channel.
+craft-web-api = { git = "https://github.com/storytold/craft-libs", rev = "fd5e2feff6ea25bed371a99cc732b3968d621505", version = "0.1.0" }
+craft-web-host = { git = "https://github.com/storytold/craft-libs", rev = "fd5e2feff6ea25bed371a99cc732b3968d621505", version = "0.1.0" }
 egui = { workspace = true }
 log = { workspace = true }
 serde_json = { workspace = true }
diff --git a/apps/gridcraft-web/src/api.rs b/apps/gridcraft-web/src/api.rs
new file mode 100644
index 000000000..74f7206f6
--- /dev/null
+++ b/apps/gridcraft-web/src/api.rs
@@ -0,0 +1,151 @@
+//! `window.gridcraft`: the page command API (`craft-web-api`, storytold/craft-libs#413) over the
+//! app's own control channel, the one the desktop control server drives (`docs/control-protocol.md`).
+//!
+//! The crate owns the JavaScript side (`request`, `execute`, `commands`, `docInspect`, `uiInspect`,
+//! `screenshot`, as promises with a timeout). This module is GridCraft's part: a [`Request`] that
+//! queues a [`ControlRequest`] for the app, which answers it on its next frame, and waits for the
+//! reply. A call the page gave up on is released ([`Pending`]), so the app drops it unrun instead of
+//! applying a command the page was told had failed.
+
+use std::sync::Arc;
+use std::sync::atomic::AtomicU8;
+use std::sync::mpsc::{Receiver, TryRecvError};
+
+use gridcraft_ui_egui::ControlRequest;
+use serde_json::{Value, json};
+
+/// How often a waiting call looks for the app's reply, in milliseconds (about a frame).
+#[cfg(target_arch = "wasm32")]
+const POLL_MS: i32 = 16;
+
+/// A queued control request whose reply has not arrived. Dropping it before the reply (the page's
+/// timeout fired, or the call was abandoned) releases the request: the app skips it unrun.
+struct Pending {
+    reply: Receiver<Value>,
+    state: Arc<AtomicU8>,
+    answered: bool,
+}
+
+impl Pending {
+    /// `Some` once the app has answered or gone away; `None` while the request is still waiting.
+    fn poll(&mut self) -> Option<Value> {
+        match self.reply.try_recv() {
+            Ok(reply) => {
+                self.answered = true;
+                Some(reply)
+            }
+            Err(TryRecvError::Empty) => None,
+            Err(TryRecvError::Disconnected) => {
+                self.answered = true;
+                Some(json!({"ok": false, "error": "the app dropped the request"}))
+            }
+        }
+    }
+}
+
+impl Drop for Pending {
+    fn drop(&mut self) {
+        if !self.answered {
+            ControlRequest::abandon(&self.state);
+        }
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+pub use web::install;
+
+#[cfg(target_arch = "wasm32")]
+mod web {
+    use std::rc::Rc;
+    use std::sync::mpsc::channel;
+
+    use craft_web_api::methods::Methods;
+    use craft_web_api::page::{PageApi, Request};
+    use gridcraft_ui_egui::{ControlRequest, SheetApp};
+    use serde_json::json;
+    use wasm_bindgen_futures::JsFuture;
+
+    use super::{POLL_MS, Pending};
+
+    /// The app id in `window.<app>`.
+    const APP: &str = "gridcraft";
+
+    /// Give the app its control queue and put `window.gridcraft` on the page. An existing
+    /// `window.gridcraft` keeps the functions it already has.
+    pub fn install(app: &mut SheetApp, ctx: egui::Context) {
+        let (queue, requests) = channel::<ControlRequest>();
+        app.control_rx = Some(requests);
+        let request: Request = Rc::new(move |method, params| {
+            let (control, reply) = ControlRequest::new(method, params);
+            let mut pending = Pending { reply, state: control.state.clone(), answered: false };
+            if queue.send(control).is_err() {
+                pending.answered = true;
+                return Box::pin(async { json!({"ok": false, "error": "the app is not running"}) });
+            }
+            ctx.request_repaint();
+            Box::pin(async move {
+                loop {
+                    if let Some(reply) = pending.poll() {
+                        return reply;
+                    }
+                    sleep(POLL_MS).await;
+                }
+            })
+        });
+        if let Err(e) = Rc::new(PageApi::new(APP, Methods::default(), request)).install() {
+            log::warn!("couldn't install window.{APP}: {e:?}");
+        }
+    }
+
+    async fn sleep(ms: i32) {
+        let promise = js_sys::Promise::new(&mut |resolve, _| {
+            if let Some(window) = web_sys::window() {
+                let _ = window.set_timeout_with_callback_and_timeout_and_arguments_0(&resolve, ms);
+            }
+        });
+        let _ = JsFuture::from(promise).await;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::atomic::Ordering;
+
+    use super::*;
+
+    /// `ControlRequest`'s `state` values (`gridcraft_ui_egui::control`): the app has started it, or its
+    /// sender gave up.
+    const TAKEN: u8 = 1;
+    const ABANDONED: u8 = 2;
+
+    fn pending() -> (Pending, ControlRequest) {
+        let (control, reply) = ControlRequest::new("document.inspect", json!({}));
+        (Pending { reply, state: control.state.clone(), answered: false }, control)
+    }
+
+    #[test]
+    fn a_call_the_page_gave_up_on_is_released_so_the_app_skips_it() {
+        let (waiting, control) = pending();
+        drop(waiting);
+        assert_eq!(control.state.load(Ordering::SeqCst), ABANDONED);
+        assert!(!control.take(), "the app must not run a request the page was told had failed");
+    }
+
+    #[test]
+    fn an_answered_call_is_not_released() {
+        let (mut waiting, control) = pending();
+        assert!(control.take());
+        control.reply.send(json!({"ok": true, "result": 1})).unwrap_or_default();
+        assert_eq!(waiting.poll(), Some(json!({"ok": true, "result": 1})));
+        drop(waiting);
+        assert_eq!(control.state.load(Ordering::SeqCst), TAKEN);
+    }
+
+    #[test]
+    fn a_request_the_app_never_runs_waits_until_it_is_dropped() {
+        let (mut waiting, control) = pending();
+        assert_eq!(waiting.poll(), None);
+        drop(control);
+        assert_eq!(waiting.poll().and_then(|r| r["ok"].as_bool()), Some(false), "the app went away");
+    }
+}
diff --git a/apps/gridcraft-web/src/main.rs b/apps/gridcraft-web/src/main.rs
index 2c701feb4..823a68e9b 100644
--- a/apps/gridcraft-web/src/main.rs
+++ b/apps/gridcraft-web/src/main.rs
@@ -13,11 +13,16 @@
 //! workbook to open and stores what GridCraft saves (`host`). A page can host GridCraft in its
 //! own document (no iframe) with `data-host="page"` on the canvas, talking over DOM `CustomEvent`s
 //! on the canvas. `&author=` names the user for notes and comments in either host mode.
+//! `window.gridcraft` (`craft-web-api`) is the page command API in every mode: `request`,
+//! `execute`, `commands`, `docInspect`, `uiInspect` and `screenshot` over the control methods
+//! (`api`).
 //! `?chrome=none|notitlebar|nofiletab` leaves the title bar and/or the File tab undrawn for a host
 //! that embeds the sheet in its own window (see `Chrome`). Preferences (theme, interface size,
 //! editing options…) are kept in `localStorage` (`prefs`).
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 
+#[cfg(any(target_arch = "wasm32", test))]
+mod api;
 #[cfg(target_arch = "wasm32")]
 mod host;
 #[cfg(any(target_arch = "wasm32", test))]
diff --git a/apps/gridcraft-web/src/web.rs b/apps/gridcraft-web/src/web.rs
index 268560520..1108c4c11 100644
--- a/apps/gridcraft-web/src/web.rs
+++ b/apps/gridcraft-web/src/web.rs
@@ -99,6 +99,7 @@ pub fn start() {
                         }
                         bridge.post_ready();
                     }
+                    crate::api::install(&mut app, cc.egui_ctx.clone());
                     Ok(Box::new(WebShell { app, inbox, bridge: app_bridge, prefs }))
                 }),
             )
diff --git a/packaging/web/README.md b/packaging/web/README.md
index 1f346cde0..833a64e9f 100644
--- a/packaging/web/README.md
+++ b/packaging/web/README.md
@@ -157,6 +157,18 @@ The messages and both transports are the shared contract of [`craft-web-host`](h
 - **Files from the host are untrusted input.** An opened file goes through the same reading as one picked with File ▸ Open or dropped on the window, with the same format limits; before it is copied into the app's memory, its size is checked against the host open limit (512 MiB) and a larger file is refused, and a name is cut to 255 characters.
 - **The event and message names are the interface.** `gridcraft:ready`, `gridcraft:open`, `gridcraft:save`, `gridcraft:dirty` and `gridcraft:failed`, and the fields they carry (the same as the `?host=parent` messages), stay stable; changing one is a breaking change.
 
+### Driving it from the page (`window.gridcraft`)
+
+Every GridCraft web build puts `window.gridcraft` on the page, from [`craft-web-api`](https://github.com/storytold/craft-libs/tree/main/crates/web-api) (storytold/craft-libs#413), the same shape in every Craft app. `gridcraft.request(method, params)` calls any method of the control channel the desktop app serves (`docs/control-protocol.md`), and `execute(command, params)`, `commands()`, `docInspect(params)`, `uiInspect(params)` and `screenshot(params)` are shortcuts for the common ones. Each returns a Promise that resolves with the method's result and rejects with an `Error`; a call the app does not answer within 30 seconds rejects, and the app drops it unrun.
+
+```js
+const book = await gridcraft.docInspect();               // sheets, used ranges, tables, charts, names, selection
+await gridcraft.execute("cell.set", { cell: "A1", input: "Total" });
+const { data } = await gridcraft.screenshot();          // the canvas as PNG (base64)
+```
+
+The API is there in every mode, with or without a host. Opening a workbook, handing a saved or exported file to the page, the file name and the unsaved flag stay with the host messages above.
+
 ## Renderer selection
 
 GridCraft's web build is the same egui app as the desktop one, compiled to wasm