diff --git a/archive/build.sh b/archive/build.sh
index 6c7df42..b272996 100644
--- a/archive/build.sh
+++ b/archive/build.sh
@@ -20,6 +20,7 @@ trap cleanup EXIT
 # CSS files to concatenate in order
 concat_files \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/base.css" \
   "css/layout.css" \
   "css/components.css" \
@@ -38,6 +39,7 @@ concat_files \
   "../shared/zddc.js" \
   "../shared/hash.js" \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/preview-lib.js" \
   "js/init.js" \
   "js/parser.js" \
diff --git a/browse/build.sh b/browse/build.sh
index 03e7f20..c9ec9b0 100755
--- a/browse/build.sh
+++ b/browse/build.sh
@@ -20,6 +20,7 @@ trap cleanup EXIT
 # CSS files: shared base first, then browse-specific.
 concat_files \
     "../shared/base.css" \
+    "../shared/toast.css" \
     "css/base.css" \
     "css/tree.css" \
     > "$css_temp"
@@ -34,6 +35,7 @@ concat_files \
     "../shared/zddc.js" \
     "../shared/zddc-filter.js" \
     "../shared/theme.js" \
+    "../shared/toast.js" \
     "../shared/help.js" \
     "../shared/preview-lib.js" \
     "js/init.js" \
diff --git a/classifier/build.sh b/classifier/build.sh
index 6bd5d95..c96ad81 100644
--- a/classifier/build.sh
+++ b/classifier/build.sh
@@ -20,6 +20,7 @@ trap cleanup EXIT
 # CSS files to concatenate in order
 concat_files \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/base.css" \
   "css/layout.css" \
   "css/spreadsheet.css" \
@@ -37,6 +38,7 @@ concat_files \
   "../shared/hash.js" \
   "../shared/zddc-source.js" \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/preview-lib.js" \
   "js/app.js" \
   "js/utils.js" \
diff --git a/classifier/css/base.css b/classifier/css/base.css
index 3274e62..ca3d4eb 100644
--- a/classifier/css/base.css
+++ b/classifier/css/base.css
@@ -28,38 +28,5 @@
     cursor: pointer;
 }
 
-/* ── Toast notifications (classifier-only) ───────────────────────────────── */
-/* shared/base.css intentionally omits toast CSS; only classifier uses toasts. */
-.toast {
-    position: fixed;
-    bottom: 2rem;
-    right: 2rem;
-    background: var(--bg);
-    color: var(--text);
-    padding: 0.875rem 1.25rem;
-    border-radius: var(--radius);
-    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
-    z-index: 9000;
-    max-width: 400px;
-    font-size: 0.875rem;
-    animation: zddc-toast-in 0.3s ease-out;
-}
-
-.toast-success { border-left: 4px solid var(--success); }
-.toast-error   { border-left: 4px solid var(--danger); }
-.toast-info    { border-left: 4px solid var(--info); }
-.toast-warning { border-left: 4px solid var(--warning); }
-
-.toast-fade {
-    animation: zddc-toast-out 0.3s ease-out forwards;
-}
-
-@keyframes zddc-toast-in {
-    from { transform: translateX(100%); opacity: 0; }
-    to   { transform: translateX(0);   opacity: 1; }
-}
-
-@keyframes zddc-toast-out {
-    from { transform: translateX(0);   opacity: 1; }
-    to   { transform: translateX(100%); opacity: 0; }
-}
+/* Toast notifications come from shared/toast.css (.zddc-toast); the
+   classifier-local .toast block was promoted there. */
diff --git a/classifier/js/excel.js b/classifier/js/excel.js
index 97a48f7..916fc78 100644
--- a/classifier/js/excel.js
+++ b/classifier/js/excel.js
@@ -6,26 +6,19 @@
     'use strict';
 
     /**
-     * Show toast notification
+     * Thin wrapper over the shared toast helper. Keeps the
+     * window.app.modules.excel.showToast call sites in classifier
+     * unchanged while delegating to the canonical implementation in
+     * shared/toast.js (window.zddc.toast).
      */
     function showToast(message, type = 'info') {
-        // Remove existing toast
-        const existing = document.querySelector('.toast');
-        if (existing) {
-            existing.remove();
+        if (window.zddc && typeof window.zddc.toast === 'function') {
+            window.zddc.toast(message, type);
+        } else {
+            // shared/toast.js missing from the build — log so the
+            // problem is visible without crashing the caller.
+            console.warn('[classifier] window.zddc.toast unavailable;', type, message);
         }
-
-        // Create toast
-        const toast = document.createElement('div');
-        toast.className = `toast toast-${type}`;
-        toast.textContent = message;
-        document.body.appendChild(toast);
-
-        // Auto-remove after 5 seconds
-        setTimeout(() => {
-            toast.classList.add('toast-fade');
-            setTimeout(() => toast.remove(), 300);
-        }, 5000);
     }
 
     /**
diff --git a/form/build.sh b/form/build.sh
index 49cf4aa..8462443 100755
--- a/form/build.sh
+++ b/form/build.sh
@@ -19,11 +19,13 @@ trap cleanup EXIT
 
 concat_files \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/form.css" \
   > "$css_temp"
 
 concat_files \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/help.js" \
   "js/app.js" \
   "js/context.js" \
diff --git a/landing/build.sh b/landing/build.sh
index dfe43c0..0abf041 100755
--- a/landing/build.sh
+++ b/landing/build.sh
@@ -19,6 +19,7 @@ trap cleanup EXIT
 
 concat_files \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/landing.css" \
   > "$css_temp"
 
@@ -26,6 +27,7 @@ concat_files \
   "../shared/zddc.js" \
   "../shared/zddc-filter.js" \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/help.js" \
   "js/landing.js" \
   > "$js_raw"
diff --git a/mdedit/build.sh b/mdedit/build.sh
index 19528c9..ac4c75c 100644
--- a/mdedit/build.sh
+++ b/mdedit/build.sh
@@ -30,6 +30,7 @@ trap cleanup EXIT
 concat_files \
   "css/tailwind-utils.css" \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/base.css" \
   "css/editor.css" \
   "css/toc.css" \
@@ -41,6 +42,7 @@ concat_files \
   "../shared/zddc.js" \
   "../shared/zddc-source.js" \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/preview-lib.js" \
   "js/app.js" \
   "js/utils.js" \
diff --git a/playwright.config.js b/playwright.config.js
index ff8bb61..65e1818 100644
--- a/playwright.config.js
+++ b/playwright.config.js
@@ -59,6 +59,10 @@ export default defineConfig({
       name: 'zddc-source',
       testMatch: 'zddc-source.spec.js',
     },
+    {
+      name: 'toast',
+      testMatch: 'toast.spec.js',
+    },
     {
       name: 'zddc',
       testMatch: 'zddc.spec.js',
diff --git a/shared/toast.css b/shared/toast.css
new file mode 100644
index 0000000..449adc9
--- /dev/null
+++ b/shared/toast.css
@@ -0,0 +1,40 @@
+/* shared/toast.css — single-toast notification styles paired with
+   shared/toast.js. Uses BEM-ish .zddc-toast prefix to avoid collisions
+   with tool-local .toast classes; the old classifier rules can stay
+   alongside until this file is concatenated above them in the build. */
+
+.zddc-toast {
+    position: fixed;
+    bottom: 2rem;
+    right: 2rem;
+    background: var(--bg);
+    color: var(--text);
+    padding: 0.875rem 1.25rem;
+    border-radius: var(--radius);
+    border: 1px solid var(--border);
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
+    z-index: 9000;
+    max-width: 400px;
+    font-size: 0.875rem;
+    cursor: pointer;
+    animation: zddc-toast-in 0.3s ease-out;
+}
+
+.zddc-toast--success { border-left: 4px solid var(--success); }
+.zddc-toast--error   { border-left: 4px solid var(--danger); }
+.zddc-toast--info    { border-left: 4px solid var(--info); }
+.zddc-toast--warning { border-left: 4px solid var(--warning); }
+
+.zddc-toast--fade {
+    animation: zddc-toast-out 0.3s ease-out forwards;
+}
+
+@keyframes zddc-toast-in {
+    from { transform: translateX(100%); opacity: 0; }
+    to   { transform: translateX(0);    opacity: 1; }
+}
+
+@keyframes zddc-toast-out {
+    from { transform: translateX(0);    opacity: 1; }
+    to   { transform: translateX(100%); opacity: 0; }
+}
diff --git a/shared/toast.js b/shared/toast.js
new file mode 100644
index 0000000..6f2a7d6
--- /dev/null
+++ b/shared/toast.js
@@ -0,0 +1,63 @@
+// shared/toast.js — non-blocking notification helper available to every
+// tool via window.zddc.toast(msg, level, opts). Originated as classifier's
+// local showToast (classifier/js/excel.js); promoted here so tools that
+// today use alert() or silent console.error can switch to a uniform
+// non-blocking surface.
+//
+// Usage:
+//   window.zddc.toast('Saved.', 'success');
+//   window.zddc.toast('Could not load: ' + err.message, 'error');
+//   window.zddc.toast('Note', 'info', { durationMs: 3000 });
+//
+// Levels: 'info' (default) | 'success' | 'warning' | 'error'.
+// Each tool may also expose app.notify(msg, level) as a thin wrapper —
+// see ARCHITECTURE.md for the convention.
+(function () {
+    'use strict';
+
+    if (!window.zddc) window.zddc = {};
+    // Don't overwrite if a tool defined its own first.
+    if (typeof window.zddc.toast === 'function') return;
+
+    var DEFAULT_DURATION_MS = 5000;
+    var FADE_MS = 300;
+
+    function toast(message, level, opts) {
+        opts = opts || {};
+        var lvl = (level === 'success' || level === 'error' ||
+                   level === 'warning') ? level : 'info';
+
+        // Single-toast policy: dismiss any existing toast immediately
+        // so the new one is always the most recent. Matches the
+        // classifier's prior behavior and avoids stack-of-toasts UX.
+        var existing = document.querySelector('.zddc-toast');
+        if (existing) existing.remove();
+
+        var el = document.createElement('div');
+        el.className = 'zddc-toast zddc-toast--' + lvl;
+        // ARIA: errors get assertive (interrupts SR queue), others polite.
+        el.setAttribute('role', lvl === 'error' ? 'alert' : 'status');
+        el.setAttribute('aria-live', lvl === 'error' ? 'assertive' : 'polite');
+        el.textContent = message == null ? '' : String(message);
+        document.body.appendChild(el);
+
+        var dur = typeof opts.durationMs === 'number' ?
+                  opts.durationMs : DEFAULT_DURATION_MS;
+        var timer = setTimeout(function () {
+            el.classList.add('zddc-toast--fade');
+            setTimeout(function () {
+                if (el.parentNode) el.parentNode.removeChild(el);
+            }, FADE_MS);
+        }, dur);
+
+        // Click-to-dismiss. Useful for sticky errors the user wants gone.
+        el.addEventListener('click', function () {
+            clearTimeout(timer);
+            if (el.parentNode) el.parentNode.removeChild(el);
+        });
+
+        return el;
+    }
+
+    window.zddc.toast = toast;
+})();
diff --git a/tables/build.sh b/tables/build.sh
index 3ce5432..1aa90ea 100755
--- a/tables/build.sh
+++ b/tables/build.sh
@@ -19,6 +19,7 @@ trap cleanup EXIT
 
 concat_files \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/table.css" \
   "../form/css/form.css" \
   > "$css_temp"
@@ -33,6 +34,7 @@ concat_files \
   "../shared/zddc.js" \
   "../shared/zddc-source.js" \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/help.js" \
   "js/mode.js" \
   "js/app.js" \
diff --git a/tests/toast.spec.js b/tests/toast.spec.js
new file mode 100644
index 0000000..752be7a
--- /dev/null
+++ b/tests/toast.spec.js
@@ -0,0 +1,67 @@
+// Tests for shared/toast.js — the cross-tool notification helper
+// available as window.zddc.toast(msg, level, opts). Loaded into every
+// tool's bundle by build.sh.
+//
+// Strategy: load any tool's dist HTML over file:// (browse is the
+// smallest), trigger the helper, and assert DOM + ARIA shape.
+
+import { test, expect } from '@playwright/test';
+import * as path from 'path';
+
+const HTML_PATH = path.resolve('browse/dist/browse.html');
+
+test.describe('shared/toast.js', () => {
+    test.beforeEach(async ({ page }) => {
+        await page.goto(`file://${HTML_PATH}`, { waitUntil: 'load' });
+    });
+
+    test('exposes window.zddc.toast(msg, level)', async ({ page }) => {
+        const exposed = await page.evaluate(
+            () => typeof window.zddc?.toast === 'function'
+        );
+        expect(exposed).toBe(true);
+    });
+
+    test('renders a single toast with the level class and ARIA role', async ({ page }) => {
+        const after = await page.evaluate(() => {
+            window.zddc.toast('Saved.', 'success');
+            const el = document.querySelector('.zddc-toast');
+            return el && {
+                text: el.textContent,
+                level: [...el.classList].find(c => c.startsWith('zddc-toast--')),
+                role: el.getAttribute('role'),
+                live: el.getAttribute('aria-live'),
+            };
+        });
+        expect(after).toEqual({
+            text: 'Saved.',
+            level: 'zddc-toast--success',
+            role: 'status',
+            live: 'polite',
+        });
+    });
+
+    test('error level uses role=alert + aria-live=assertive', async ({ page }) => {
+        const probe = await page.evaluate(() => {
+            window.zddc.toast('Boom', 'error');
+            const el = document.querySelector('.zddc-toast');
+            return { role: el.getAttribute('role'), live: el.getAttribute('aria-live') };
+        });
+        expect(probe).toEqual({ role: 'alert', live: 'assertive' });
+    });
+
+    test('a second toast replaces the first (single-toast policy)', async ({ page }) => {
+        const count = await page.evaluate(() => {
+            window.zddc.toast('one', 'info');
+            window.zddc.toast('two', 'info');
+            return document.querySelectorAll('.zddc-toast').length;
+        });
+        expect(count).toBe(1);
+    });
+
+    test('clicking dismisses immediately', async ({ page }) => {
+        await page.evaluate(() => window.zddc.toast('click me', 'info'));
+        await page.locator('.zddc-toast').click();
+        await expect(page.locator('.zddc-toast')).toHaveCount(0);
+    });
+});
diff --git a/transmittal/build.sh b/transmittal/build.sh
index 4ed9acb..ebf75de 100755
--- a/transmittal/build.sh
+++ b/transmittal/build.sh
@@ -23,6 +23,7 @@ trap cleanup EXIT
 # CSS files to concatenate in order
 concat_files \
   "../shared/base.css" \
+  "../shared/toast.css" \
   "css/base.css" \
   "css/layout.css" \
   "css/forms.css" \
@@ -47,6 +48,7 @@ concat_files \
   "../shared/hash.js" \
   "../shared/zddc-source.js" \
   "../shared/theme.js" \
+  "../shared/toast.js" \
   "../shared/preview-lib.js" \
   "js/app.js" \
   "js/reactive.js" \
diff --git a/zddc/internal/handler/tables.html b/zddc/internal/handler/tables.html
index 1e4dc80..a8c17bb 100644
--- a/zddc/internal/handler/tables.html
+++ b/zddc/internal/handler/tables.html
@@ -335,6 +335,11 @@ a:hover {
     font-size: 1rem;
 }
 
+/* The refresh ⟳ glyph renders slightly smaller than ◐ / ? — bump to match. */
+#refreshHeaderBtn {
+    font-size: 1.1rem;
+}
+
 /* Toast CSS lives in classifier/css/base.css — only that tool uses toasts. */
 
 /* ── Theme and help icon buttons ─────────────────────────────────────────── */
@@ -525,6 +530,47 @@ body.help-open .app-header {
     color: var(--text-muted);
 }
 
+/* shared/toast.css — single-toast notification styles paired with
+   shared/toast.js. Uses BEM-ish .zddc-toast prefix to avoid collisions
+   with tool-local .toast classes; the old classifier rules can stay
+   alongside until this file is concatenated above them in the build. */
+
+.zddc-toast {
+    position: fixed;
+    bottom: 2rem;
+    right: 2rem;
+    background: var(--bg);
+    color: var(--text);
+    padding: 0.875rem 1.25rem;
+    border-radius: var(--radius);
+    border: 1px solid var(--border);
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
+    z-index: 9000;
+    max-width: 400px;
+    font-size: 0.875rem;
+    cursor: pointer;
+    animation: zddc-toast-in 0.3s ease-out;
+}
+
+.zddc-toast--success { border-left: 4px solid var(--success); }
+.zddc-toast--error   { border-left: 4px solid var(--danger); }
+.zddc-toast--info    { border-left: 4px solid var(--info); }
+.zddc-toast--warning { border-left: 4px solid var(--warning); }
+
+.zddc-toast--fade {
+    animation: zddc-toast-out 0.3s ease-out forwards;
+}
+
+@keyframes zddc-toast-in {
+    from { transform: translateX(100%); opacity: 0; }
+    to   { transform: translateX(0);    opacity: 1; }
+}
+
+@keyframes zddc-toast-out {
+    from { transform: translateX(0);    opacity: 1; }
+    to   { transform: translateX(100%); opacity: 0; }
+}
+
 /* tables/ — directory-of-YAML table view. Reuses tokens from shared/base.css. */
 
 .table-main {
@@ -967,7 +1013,7 @@ body.help-open .app-header {
             </svg>
             <div class="header-title-group">
                 <span class="app-header__title" id="table-title">ZDDC Table</span>
-                <span class="build-timestamp"><span style="color:red;font-weight:bold">v0.0.17-alpha · 2026-05-09 23:35:43 · 3a4a1c7-dirty</span></span>
+                <span class="build-timestamp"><span style="color:red;font-weight:bold">v0.0.17-alpha · 2026-05-10 00:02:54 · 538167b-dirty</span></span>
             </div>
         </div>
         <div class="header-right">
@@ -1965,6 +2011,70 @@ body.help-open .app-header {
     }
 }());
 
+// shared/toast.js — non-blocking notification helper available to every
+// tool via window.zddc.toast(msg, level, opts). Originated as classifier's
+// local showToast (classifier/js/excel.js); promoted here so tools that
+// today use alert() or silent console.error can switch to a uniform
+// non-blocking surface.
+//
+// Usage:
+//   window.zddc.toast('Saved.', 'success');
+//   window.zddc.toast('Could not load: ' + err.message, 'error');
+//   window.zddc.toast('Note', 'info', { durationMs: 3000 });
+//
+// Levels: 'info' (default) | 'success' | 'warning' | 'error'.
+// Each tool may also expose app.notify(msg, level) as a thin wrapper —
+// see ARCHITECTURE.md for the convention.
+(function () {
+    'use strict';
+
+    if (!window.zddc) window.zddc = {};
+    // Don't overwrite if a tool defined its own first.
+    if (typeof window.zddc.toast === 'function') return;
+
+    var DEFAULT_DURATION_MS = 5000;
+    var FADE_MS = 300;
+
+    function toast(message, level, opts) {
+        opts = opts || {};
+        var lvl = (level === 'success' || level === 'error' ||
+                   level === 'warning') ? level : 'info';
+
+        // Single-toast policy: dismiss any existing toast immediately
+        // so the new one is always the most recent. Matches the
+        // classifier's prior behavior and avoids stack-of-toasts UX.
+        var existing = document.querySelector('.zddc-toast');
+        if (existing) existing.remove();
+
+        var el = document.createElement('div');
+        el.className = 'zddc-toast zddc-toast--' + lvl;
+        // ARIA: errors get assertive (interrupts SR queue), others polite.
+        el.setAttribute('role', lvl === 'error' ? 'alert' : 'status');
+        el.setAttribute('aria-live', lvl === 'error' ? 'assertive' : 'polite');
+        el.textContent = message == null ? '' : String(message);
+        document.body.appendChild(el);
+
+        var dur = typeof opts.durationMs === 'number' ?
+                  opts.durationMs : DEFAULT_DURATION_MS;
+        var timer = setTimeout(function () {
+            el.classList.add('zddc-toast--fade');
+            setTimeout(function () {
+                if (el.parentNode) el.parentNode.removeChild(el);
+            }, FADE_MS);
+        }, dur);
+
+        // Click-to-dismiss. Useful for sticky errors the user wants gone.
+        el.addEventListener('click', function () {
+            clearTimeout(timer);
+            if (el.parentNode) el.parentNode.removeChild(el);
+        });
+
+        return el;
+    }
+
+    window.zddc.toast = toast;
+})();
+
 /**
  * ZDDC shared help panel — open/close logic.
  * Works with all four tools regardless of their module pattern.