diff --git a/app.py b/app.py
index b0164e7..143fade 100644
--- a/app.py
+++ b/app.py
@@ -2,7 +2,7 @@
 from __future__ import annotations
 
 import click
-from flask import Flask
+from flask import Flask, render_template
 
 from auth import current_user_id, is_logged_in
 from config import Config
@@ -42,6 +42,14 @@ def create_app(config_overrides: dict | None = None) -> Flask:
     app.register_blueprint(account_bp)
     app.register_blueprint(leagues_bp)
 
+    @app.errorhandler(404)
+    def not_found(e):
+        return render_template("404.html"), 404
+
+    @app.errorhandler(403)
+    def forbidden(e):
+        return render_template("403.html"), 403
+
     @app.cli.command("init-db")
     def init_db_command() -> None:
         if not database_extensions_available() or db is None:
diff --git a/config.py b/config.py
index 38f0056..1c128a4 100644
--- a/config.py
+++ b/config.py
@@ -9,7 +9,7 @@ DATA_PATH = BASE_DIR / "data" / "entries.csv"
 DEFAULT_DATABASE_URL = f"sqlite:///{BASE_DIR / 'data' / 'boker-dev.sqlite3'}"
 
 ELIGIBLE_MIN_SESSIONS = 3
-APP_VERSION = "2.5.10"
+APP_VERSION = "2.5.11"
 
 
 def load_local_env(env_path: Path) -> None:
diff --git a/static/css/style.css b/static/css/style.css
index 28145ff..efc6a39 100644
--- a/static/css/style.css
+++ b/static/css/style.css
@@ -5604,6 +5604,91 @@ select.control { cursor: pointer; }
   }
 }
 
+/* ================================================================
+   ERROR PAGES (404, 403)
+   ================================================================ */
+.page--error {
+  padding: 0;
+  max-width: none;
+}
+
+.error-pg {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  min-height: calc(100vh - 62px);
+  position: relative;
+  overflow: hidden;
+  background:
+    radial-gradient(ellipse 90% 70% at 50% 60%, #1c0e3e 0%, #100820 55%, var(--bg) 100%),
+    radial-gradient(ellipse 50% 40% at 80% 20%, rgba(155,140,240,.07) 0%, transparent 55%);
+}
+
+/* large suit watermark */
+.error-pg__suit {
+  position: absolute;
+  font-size: clamp(320px, 46vw, 660px);
+  color: rgba(155,140,240,.065);
+  line-height: 1;
+  pointer-events: none;
+  user-select: none;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+  transition: none;
+}
+.error-pg--403 .error-pg__suit {
+  color: rgba(155,140,240,.06);
+}
+
+.error-pg__body {
+  position: relative;
+  z-index: 1;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  text-align: center;
+  gap: 0;
+  padding: clamp(32px, 5vw, 64px) clamp(24px, 5vw, 48px);
+}
+
+.error-pg__code {
+  font-family: var(--font-mono);
+  font-size: clamp(80px, 13vw, 148px);
+  font-weight: 900;
+  letter-spacing: -.04em;
+  line-height: 1;
+  background: linear-gradient(135deg, var(--accent) 0%, rgba(155,140,240,.35) 100%);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+  margin-bottom: 8px;
+}
+
+.error-pg__title {
+  font-size: clamp(28px, 4vw, 52px);
+  font-weight: 800;
+  color: var(--text);
+  letter-spacing: -.04em;
+  margin: 0 0 16px;
+  line-height: 1.1;
+}
+
+.error-pg__sub {
+  font-size: clamp(14px, 1.3vw, 16px);
+  color: rgba(255,255,255,.42);
+  max-width: 40ch;
+  line-height: 1.68;
+  margin: 0 0 28px;
+}
+
+.error-pg__actions {
+  display: flex;
+  gap: 12px;
+  flex-wrap: wrap;
+  justify-content: center;
+}
+
 /* ================================================================
    LANDING — hero kicker (replaces pill eyebrow in hero only)
    ================================================================ */
diff --git a/templates/403.html b/templates/403.html
new file mode 100644
index 0000000..625f376
--- /dev/null
+++ b/templates/403.html
@@ -0,0 +1,23 @@
+{% extends "base.html" %}
+{% block title %}403 · Access Denied · myboker.org{% endblock %}
+{% block page_class %}page--error{% endblock %}
+{% block content %}
+
+<div class="error-pg error-pg--403">
+    <div class="error-pg__suit" aria-hidden="true">♣</div>
+    <div class="error-pg__body">
+        <span class="error-pg__code">403</span>
+        <h1 class="error-pg__title">Access denied.</h1>
+        <p class="error-pg__sub">You don't have permission to view this page. If you think this is a mistake, contact your league owner.</p>
+        <div class="error-pg__actions">
+            <a class="btn btn--primary btn--lg" href="{{ url_for('public.home') }}">Go home →</a>
+            {% if not is_logged_in %}
+            <a class="btn btn--ghost btn--lg" href="{{ url_for('account.login') }}">Sign in</a>
+            {% else %}
+            <a class="btn btn--ghost btn--lg" href="javascript:history.back()">Go back</a>
+            {% endif %}
+        </div>
+    </div>
+</div>
+
+{% endblock %}
diff --git a/templates/404.html b/templates/404.html
new file mode 100644
index 0000000..22dc7f9
--- /dev/null
+++ b/templates/404.html
@@ -0,0 +1,19 @@
+{% extends "base.html" %}
+{% block title %}404 · Page Not Found · myboker.org{% endblock %}
+{% block page_class %}page--error{% endblock %}
+{% block content %}
+
+<div class="error-pg">
+    <div class="error-pg__suit" aria-hidden="true">♠</div>
+    <div class="error-pg__body">
+        <span class="error-pg__code">404</span>
+        <h1 class="error-pg__title">Page not found.</h1>
+        <p class="error-pg__sub">That URL doesn't exist or the page has been moved. Double-check the address or head back to safety.</p>
+        <div class="error-pg__actions">
+            <a class="btn btn--primary btn--lg" href="{{ url_for('public.home') }}">Go home →</a>
+            <a class="btn btn--ghost btn--lg" href="javascript:history.back()">Go back</a>
+        </div>
+    </div>
+</div>
+
+{% endblock %}