diff --git a/src/ViperIDE.html b/src/ViperIDE.html
index d7dbd76..0900c1a 100644
--- a/src/ViperIDE.html
+++ b/src/ViperIDE.html
@@ -32,6 +32,7 @@
             <button title="Run File [F5]"        onclick="app.runCurrentFile()"  id="btn-run"><i class="fa-solid fa-circle-play" id="btn-run-icon"></i></button>
         </div>
         <div>
+            <span id="boot-status" role="status" hidden><i class="fa-solid fa-spinner fa-spin"></i> <span id="boot-status-text">Starting…</span></span>
             <button title="Simulator (virtual device)" onclick="app.connectDevice('sim')" id="btn-conn-sim" disabled><i class="fa-solid fa-display"></i></button>
             <button title="Connect WebREPL"      onclick="app.connectDevice('ws')"  id="btn-conn-ws" disabled ><i class="fa-solid fa-link"></i></button>
             <button title="Connect Bluetooth"    onclick="app.connectDevice('ble')" id="btn-conn-ble" disabled><i class="fa-brands fa-bluetooth-b"></i></button>
diff --git a/src/app.js b/src/app.js
index f91634b..3a7a01f 100644
--- a/src/app.js
+++ b/src/app.js
@@ -491,6 +491,16 @@ function wirePort(new_port) {
     new_port.onDisconnect(handlePortDisconnect)
 }
 
+/* The "starting" sign: a spinner and a word beside the connect buttons, and
+   the clicked button pulsing. Cleared by the caller on success and failure. */
+function setBooting(on, type) {
+    QID('boot-status').hidden = !on
+    QID('boot-status-text').textContent = (type === 'sim') ? 'Starting simulator…' : 'Connecting…'
+    for (const t of ['sim', 'ws', 'ble', 'usb']) {
+        QID(`btn-conn-${t}`).classList.toggle('booting', on && t === type)
+    }
+}
+
 export async function connectDevice(type) {
     if (port) {
         const msg = (deviceState === 'reconnecting') ? 'Stop reconnecting and disconnect?'
@@ -500,12 +510,26 @@ export async function connectDevice(type) {
         return
     }
 
-    const new_port = await prepareNewPort(type)
-    if (!new_port) { return }
-    /* A ?vm=1 link arrives as type 'ws' but hands back the simulator; from
-       here on everything - connType, the stage, audio, the button highlight -
-       should treat it as what it is. */
-    if (new_port.isSimulator) { type = 'sim' }
+    /* Booting the simulator takes a while, and most of it is inside
+       prepareNewPort (requestAccess starts the VM): say so from the click
+       until the prompt is up, whether that ends in a session or an error.
+       Other connections only start once their picker has been answered. */
+    setBooting(type === 'sim', type)
+    try {
+        const new_port = await prepareNewPort(type)
+        if (!new_port) { return }
+        /* A ?vm=1 link arrives as type 'ws' but hands back the simulator; from
+           here on everything - connType, the stage, audio, the button highlight -
+           should treat it as what it is. */
+        if (new_port.isSimulator) { type = 'sim' }
+        setBooting(true, type)
+        await bringUpPort(new_port, type)
+    } finally {
+        setBooting(false)
+    }
+}
+
+async function bringUpPort(new_port, type) {
     // Connect new port
     try {
         await new_port.connect()
diff --git a/src/app_common.css b/src/app_common.css
index 6ec114e..d992252 100644
--- a/src/app_common.css
+++ b/src/app_common.css
@@ -152,12 +152,23 @@ button.reconnecting {
     animation: reconnecting-pulse 1.2s ease-in-out infinite;
 }
 
+/* The simulator or a board is coming up after a click on Connect */
+button.booting {
+    animation: reconnecting-pulse 1.2s ease-in-out infinite;
+}
+
+#boot-status {
+    font-size: 0.9rem;
+    opacity: 0.85;
+    white-space: nowrap;
+}
+
 @keyframes reconnecting-pulse {
     50% { opacity: 0.25; }
 }
 
 @media (prefers-reduced-motion: reduce) {
-    button.reconnecting {
+    button.reconnecting, button.booting {
         animation: none;
         opacity: 0.6;
     }
diff --git a/test/browser/booting-indicator.spec.js b/test/browser/booting-indicator.spec.js
new file mode 100644
index 0000000..e835bbb
--- /dev/null
+++ b/test/browser/booting-indicator.spec.js
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: MIT
+//
+// Launching the simulator used to show nothing until the board appeared, so
+// the click looked ignored. The page now shows a "Starting" status from the
+// click until the prompt is up, and clears it when the boot fails too.
+import { test, expect } from '@playwright/test'
+
+test('a booting indicator shows from the click until the prompt is up', async ({ page }) => {
+    await page.goto('/')
+    const status = page.locator('#boot-status')
+    await expect(status).toBeHidden()
+    await page.click('#btn-conn-sim')
+    await expect(status).toBeVisible({ timeout: 2000 })
+    await expect(status).toContainText('Starting')
+    await expect(page.locator('#btn-conn-sim')).toHaveClass(/booting/)
+    await expect(page.locator('#xterm')).toContainText('>>>', { timeout: 45_000 })
+    await expect(status).toBeHidden()
+    await expect(page.locator('#btn-conn-sim')).not.toHaveClass(/booting/)
+})
+
+test('the booting indicator shows, then clears, when the simulator fails to start', async ({ page }) => {
+    await page.route('**/micropython.wasm', (route) => route.abort())
+    await page.goto('/')
+    // A failed boot can be over in well under a poll, so watch for the sign
+    // from inside the page instead of racing it.
+    await page.evaluate(() => {
+        const el = document.getElementById('boot-status')
+        window.__sawBooting = false
+        new MutationObserver(() => { if (!el.hidden) window.__sawBooting = true })
+            .observe(el, { attributes: true, attributeFilter: ['hidden'] })
+    })
+    await page.click('#btn-conn-sim')
+    await expect.poll(() => page.evaluate(() => window.__sawBooting), { timeout: 30_000 }).toBe(true)
+    await expect(page.locator('#boot-status')).toBeHidden({ timeout: 30_000 })
+    await expect(page.locator('#btn-conn-sim')).not.toHaveClass(/booting/)
+    await expect(page.locator('#xterm')).not.toContainText('>>>')
+})