diff --git a/package-lock.json b/package-lock.json
index c6a082f..be1aa15 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2720,9 +2720,9 @@
       }
     },
     "node_modules/caniuse-lite": {
-      "version": "1.0.30001702",
-      "resolved": "https://registry.npmjs.org/caniuse-lite/-/caniuse-lite-1.0.30001702.tgz",
-      "integrity": "sha512-LoPe/D7zioC0REI5W73PeR1e1MLCipRGq/VkovJnd6Df+QVqT+vT33OXCp8QUd7kA7RZrHWxb1B36OQKI/0gOA==",
+      "version": "1.0.30001757",
+      "resolved": "https://registry.npmjs.org/caniuse-lite/-/caniuse-lite-1.0.30001757.tgz",
+      "integrity": "sha512-r0nnL/I28Zi/yjk1el6ilj27tKcdjLsNqAOZr0yVjWPrSQyHgKI2INaEWw21bAQSv2LXRt1XuCS/GomNpWOxsQ==",
       "dev": true,
       "funding": [
         {
diff --git a/src/lib/Toasts.svelte b/src/lib/Toasts.svelte
new file mode 100644
index 0000000..e7f33e0
--- /dev/null
+++ b/src/lib/Toasts.svelte
@@ -0,0 +1,84 @@
+<script lang="ts" module>
+  export type Toast = {
+    message: string;
+    style?: "error";
+  };
+
+  export function showToast(toast: Toast) {
+    toastQueue.push(toast);
+    mainLoop();
+  }
+
+  let toastQueue: Toast[] = [];
+  let currentToast: Toast | undefined = $state();
+
+  let active = false;
+  async function mainLoop() {
+    if (active) {
+      return;
+    }
+
+    active = true;
+
+    while (toastQueue.length > 0) {
+      currentToast = toastQueue.shift();
+      await wait(5_000);
+
+      currentToast = undefined;
+      await wait(1_000);
+    }
+
+    active = false;
+  }
+
+  function wait(ms: number): Promise<void> {
+    return new Promise((resolve) => setTimeout(resolve, ms));
+  }
+</script>
+
+<script lang="ts">
+  import "$lib/hexagons.css";
+  import { fade, fly } from "svelte/transition";
+
+  let height: number = $state(48);
+</script>
+
+{#if currentToast != undefined}
+  <div
+    class="toast clip-hexagon {currentToast.style}"
+    in:fly={{ y: "100%" }}
+    out:fade
+    bind:clientHeight={height}
+    style:--height="{height}px"
+  >
+    {currentToast.message}
+  </div>
+{/if}
+
+<style>
+  .toast {
+    color: var(--background-color);
+    background-color: var(--foreground-color);
+    font-size: 14pt;
+    font-weight: 400;
+    position: fixed;
+    left: 0;
+    bottom: 0;
+    margin: 24px;
+    min-height: 48px;
+    padding: 12px calc(var(--height) / 3.4641 + 6px);
+    display: grid;
+    place-content: center;
+  }
+
+  .toast.error {
+    background-color: var(--red);
+    color: white;
+  }
+
+  @media (width < 600px) {
+    .toast {
+      right: 0;
+    }
+  }
+</style>
diff --git a/src/lib/errors.test.ts b/src/lib/errors.test.ts
new file mode 100644
index 0000000..ad09d9e
--- /dev/null
+++ b/src/lib/errors.test.ts
@@ -0,0 +1,12 @@
+import { describe, expect, it } from "vitest";
+import { getErrorMessage } from "./errors";
+
+describe("getErrorMessage", () => {
+  it("should return string unchanged", () => {
+    expect(getErrorMessage("example string")).toBe("example string");
+  });
+
+  it("should get message from error", () => {
+    expect(getErrorMessage(new Error("example message"))).toBe("example message");
+  });
+});
diff --git a/src/lib/errors.ts b/src/lib/errors.ts
new file mode 100644
index 0000000..bfb4753
--- /dev/null
+++ b/src/lib/errors.ts
@@ -0,0 +1,42 @@
+import { showToast } from "./Toasts.svelte";
+
+export function getErrorMessage(error: unknown): string {
+  if (typeof error == "string") {
+    return error;
+  }
+
+  if (
+    typeof error == "object" &&
+    error != null &&
+    "message" in error &&
+    typeof error.message == "string"
+  ) {
+    return error.message;
+  }
+
+  console.error("unknown error", error);
+  return String(error);
+}
+
+export function toastError(error: unknown) {
+  console.error(error);
+
+  const message = getErrorMessage(error);
+
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-call -- this is just eslint getting confused by svelte
+  showToast({ message, style: "error" });
+}
+
+export async function assertOk(response: Response | Promise<Response>): Promise<Response> {
+  response = await response;
+
+  if (response.ok) {
+    return response;
+  }
+
+  if (response.headers.get("Content-Type")?.startsWith("application/json")) {
+    throw await response.json();
+  } else {
+    throw await response.text();
+  }
+}
diff --git a/src/lib/themes.css b/src/lib/themes.css
index 5fba398..6ac48ab 100644
--- a/src/lib/themes.css
+++ b/src/lib/themes.css
@@ -1,7 +1,7 @@
 :root {
   color-scheme: light dark;
-  background-color: light-dark(white, #121212);
-  color: light-dark(black, white);
+  background-color: var(--background-color);
+  color: var(--foreground-color);
   accent-color: var(--primary);
 
   --red: oklch(57% 0.26 28deg);
@@ -12,4 +12,6 @@
   --purple: oklch(48% 0.24 311deg);
   --pink: oklch(77% 0.19 356deg);
   --primary: light-dark(var(--blue), var(--aqua));
+  --background-color: light-dark(white, #121212);
+  --foreground-color: light-dark(black, white);
 }
diff --git a/src/routes/+layout.svelte b/src/routes/+layout.svelte
index ce9bd52..e7cc81b 100644
--- a/src/routes/+layout.svelte
+++ b/src/routes/+layout.svelte
@@ -13,6 +13,8 @@
   import Modal from "$lib/Modal.svelte";
   import EditNameForm from "$lib/EditNameForm.svelte";
   import AccountModal from "$lib/AccountModal.svelte";
+  import Toasts from "$lib/Toasts.svelte";
+  import { toastError } from "$lib/errors.js";
 
   let { data, children } = $props();
   let { supabase, session, user, profilePromise, lightModeCookie } = $derived(data);
@@ -54,6 +56,11 @@
   <link rel="preconnect" href={PUBLIC_SUPABASE_URL} />
 </svelte:head>
 
+<svelte:window
+  onerror={(event) => toastError(event instanceof ErrorEvent ? event.error : event)}
+  onunhandledrejection={(event) => toastError(event.reason)}
+/>
+
 <header>
   <h1><a href="/">Connexagon</a></h1>
 
@@ -78,6 +85,8 @@
   <AccountModal {supabase} {user} {profilePromise} bind:open={showAccountModal} />
 {/if}
 
+<Toasts />
+
 <style>
   header {
     padding: 12px;
diff --git a/src/routes/games/[game_id]/+page.svelte b/src/routes/games/[game_id]/+page.svelte
index 0094270..6c9c7fd 100644
--- a/src/routes/games/[game_id]/+page.svelte
+++ b/src/routes/games/[game_id]/+page.svelte
@@ -6,6 +6,7 @@
   import Board from "$lib/Board.svelte";
   import Button from "$lib/Button.svelte";
   import type { Tables } from "$lib/database-types";
+  import { assertOk } from "$lib/errors.js";
 
   const { data } = $props();
   const { supabase, user } = $derived(data);
@@ -99,11 +100,16 @@
   let selection: number[] = $state([]);
 
   async function startGame() {
-    await fetch(`/games/${game.id}/start`, { method: "POST" });
+    await assertOk(fetch(`/games/${game.id}/start`, { method: "POST" }));
   }
 
   async function makeTurn() {
-    await fetch(`/games/${game.id}/turns`, { method: "POST", body: JSON.stringify(selection) });
+    await assertOk(
+      fetch(`/games/${game.id}/turns`, {
+        method: "POST",
+        body: JSON.stringify(selection),
+      }),
+    );
     selection = [];
   }