diff --git a/README.md b/README.md
index a778eae..c389c35 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,24 @@
 # analyse
 
+> [!WARNING]
+> **webpack analyse is deprecated.** It is no longer maintained and will not
+> gain new features. Use
+> [webpack-bundle-analyzer](https://github.com/webpack/webpack-bundle-analyzer)
+> instead: it reads the same `stats.json`, runs as a webpack plugin or from the
+> command line, and is where the work continues. The features this app has that
+> bundle-analyzer does not yet are tracked in
+> [webpack-bundle-analyzer#737](https://github.com/webpack/webpack-bundle-analyzer/issues/737).
+>
+> Moving over:
+>
+> ```bash
+> npm install --save-dev webpack-bundle-analyzer
+> npx webpack-bundle-analyzer stats.json
+> ```
+>
+> The site stays up and the repository stays open so existing links keep
+> working, but expect fixes only for what breaks outright.
+
 A browser-based dashboard for exploring webpack bundle statistics. It reads a webpack stats JSON file and visualizes modules, chunks, assets, warnings, errors, and optimization hints so you can understand bundle size and dependency structure.
 
 This project is a lightweight front-end viewer for webpack output generated with `--profile --json`.
diff --git a/app/deprecation.pug b/app/deprecation.pug
new file mode 100644
index 0000000..bf82753
--- /dev/null
+++ b/app/deprecation.pug
@@ -0,0 +1,7 @@
+//- Shown on every page: both application shells include it. Keep the wording
+//- in step with the notice at the top of README.md.
+.deprecation-banner(role="status")
+	strong webpack analyse is deprecated.
+	|  It is no longer maintained and will not gain new features. Use
+	|  #[a(href="https://github.com/webpack/webpack-bundle-analyzer", target="_blank", rel="noopener noreferrer") webpack-bundle-analyzer]
+	|  instead — it reads the same stats file and is where the work continues.
diff --git a/app/pages/select/application.pug b/app/pages/select/application.pug
index aee0546..62e1b87 100644
--- a/app/pages/select/application.pug
+++ b/app/pages/select/application.pug
@@ -1,3 +1,4 @@
+include ../../deprecation.pug
 nav.navbar.navbar-default
 	.container-fluid
 		ul.nav.navbar-nav
diff --git a/app/pages/upload/application.pug b/app/pages/upload/application.pug
index 2200441..41af5f7 100644
--- a/app/pages/upload/application.pug
+++ b/app/pages/upload/application.pug
@@ -1,3 +1,4 @@
+include ../../deprecation.pug
 nav.navbar.navbar-default
 	.container-fluid
 		ul.nav.navbar-nav
diff --git a/app/style.css b/app/style.css
index 8de293b..8cda084 100644
--- a/app/style.css
+++ b/app/style.css
@@ -135,3 +135,16 @@ table pre {
 .module-filter-summary {
 	color: #777;
 }
+
+/* Deprecation notice above the navbar, on every page. Bootstrap 3 has no
+   colour for "retired", so this borrows the warning palette a shade darker. */
+.deprecation-banner {
+	padding: 10px 15px;
+	border-bottom: 1px solid #f0c36d;
+	background: #fcf5d8;
+	color: #7a5b13;
+}
+.deprecation-banner a {
+	color: #7a5b13;
+	text-decoration: underline;
+}
diff --git a/test/deprecation.test.js b/test/deprecation.test.js
new file mode 100644
index 0000000..cbd6517
--- /dev/null
+++ b/test/deprecation.test.js
@@ -0,0 +1,27 @@
+// The deprecation notice is the one thing every visitor has to see, and it
+// lives in a partial two shells include. Run with `npm test`.
+var test = require("node:test");
+var assert = require("node:assert");
+var path = require("node:path");
+var pug = require("pug");
+
+var shells = {
+	upload: { file: "app/pages/upload/application.pug", locals: {} },
+	select: { file: "app/pages/select/application.pug", locals: { children: [] } }
+};
+
+Object.keys(shells).forEach(function(name) {
+	test("the " + name + " shell carries the deprecation notice", function() {
+		var shell = shells[name];
+		var html = pug.renderFile(
+			path.join(__dirname, "..", shell.file),
+			shell.locals
+		);
+		assert.match(html, /webpack analyse is deprecated/);
+		assert.match(
+			html,
+			/https:\/\/github\.com\/webpack\/webpack-bundle-analyzer/,
+			"and points at what replaces it"
+		);
+	});
+});