diff --git a/web/public/assets/js/app/__tests__/message-limit.test.js b/web/public/assets/js/app/__tests__/message-limit.test.js
new file mode 100644
index 0000000..257811a
--- /dev/null
+++ b/web/public/assets/js/app/__tests__/message-limit.test.js
@@ -0,0 +1,41 @@
+/*
+ * Copyright © 2025-26 l5yth & contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import { MESSAGE_LIMIT, normaliseMessageLimit } from '../message-limit.js';
+
+test('normaliseMessageLimit defaults to the message limit for invalid input', () => {
+  assert.equal(normaliseMessageLimit(undefined), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit(null), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit(''), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit('abc'), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit(-100), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit(0), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit(Number.POSITIVE_INFINITY), MESSAGE_LIMIT);
+});
+
+test('normaliseMessageLimit clamps numeric input to the upper bound', () => {
+  assert.equal(normaliseMessageLimit(MESSAGE_LIMIT + 1), MESSAGE_LIMIT);
+  assert.equal(normaliseMessageLimit(MESSAGE_LIMIT * 2), MESSAGE_LIMIT);
+});
+
+test('normaliseMessageLimit accepts positive finite values', () => {
+  assert.equal(normaliseMessageLimit(250), 250);
+  assert.equal(normaliseMessageLimit('750'), 750);
+  assert.equal(normaliseMessageLimit(42.9), 42);
+});
diff --git a/web/public/assets/js/app/main.js b/web/public/assets/js/app/main.js
index 80174be..b4c7821 100644
--- a/web/public/assets/js/app/main.js
+++ b/web/public/assets/js/app/main.js
@@ -38,6 +38,7 @@ import {
   formatChatPresetTag
 } from './chat-format.js';
 import { initializeInstanceSelector } from './instance-selector.js';
+import { MESSAGE_LIMIT, normaliseMessageLimit } from './message-limit.js';
 import { CHAT_LOG_ENTRY_TYPES, buildChatTabModel, MAX_CHANNEL_INDEX } from './chat-log-tabs.js';
 import { renderChatTabs } from './chat-tabs.js';
 import { formatPositionHighlights, formatTelemetryHighlights } from './chat-log-highlights.js';
@@ -142,7 +143,7 @@ let messagesById = new Map();
     logger: console,
   });
   const NODE_LIMIT = 1000;
-  const CHAT_LIMIT = 1000;
+  const CHAT_LIMIT = MESSAGE_LIMIT;
   const CHAT_RECENT_WINDOW_SECONDS = 7 * 24 * 60 * 60;
   const REFRESH_MS = config.refreshMs;
   const CHAT_ENABLED = Boolean(config.chatEnabled);
@@ -2997,9 +2998,10 @@ let messagesById = new Map();
    * @param {number} [limit=NODE_LIMIT] Maximum number of rows.
    * @returns {Promise<Array<Object>>} Parsed message payloads.
    */
-  async function fetchMessages(limit = NODE_LIMIT) {
+  async function fetchMessages(limit = MESSAGE_LIMIT) {
     if (!CHAT_ENABLED) return [];
-    const r = await fetch(`/api/messages?limit=${limit}`, { cache: 'no-store' });
+    const safeLimit = normaliseMessageLimit(limit);
+    const r = await fetch(`/api/messages?limit=${safeLimit}`, { cache: 'no-store' });
     if (!r.ok) throw new Error('HTTP ' + r.status);
     return r.json();
   }
@@ -3636,7 +3638,7 @@ let messagesById = new Map();
         fetchNodes(),
         positionsPromise,
         neighborPromise,
-        fetchMessages(),
+        fetchMessages(MESSAGE_LIMIT),
         telemetryPromise,
       ]);
       nodes.forEach(applyNodeNameFallback);
diff --git a/web/public/assets/js/app/message-limit.js b/web/public/assets/js/app/message-limit.js
new file mode 100644
index 0000000..0dd653c
--- /dev/null
+++ b/web/public/assets/js/app/message-limit.js
@@ -0,0 +1,43 @@
+/*
+ * Copyright © 2025-26 l5yth & contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Maximum number of chat messages that the API can return in a single request.
+ * @type {number}
+ */
+export const MESSAGE_LIMIT = 1000;
+
+/**
+ * Normalise a candidate limit for the messages API to remain within supported bounds.
+ *
+ * The API clamps responses to {@link MESSAGE_LIMIT}, so this helper ensures the
+ * frontend always requests an allowed value while defaulting to the upper bound
+ * when callers omit or provide invalid data.
+ *
+ * @param {*} limit Candidate limit value supplied by the caller.
+ * @returns {number} Safe, positive limit capped at {@link MESSAGE_LIMIT}.
+ */
+export function normaliseMessageLimit(limit) {
+  const parsed = Number.parseFloat(limit);
+  if (!Number.isFinite(parsed) || parsed <= 0) {
+    return MESSAGE_LIMIT;
+  }
+  const floored = Math.floor(parsed);
+  if (floored <= 0) {
+    return MESSAGE_LIMIT;
+  }
+  return Math.min(floored, MESSAGE_LIMIT);
+}