diff --git a/lib/ai.js b/lib/ai.js
index f25c1f5..c107082 100644
--- a/lib/ai.js
+++ b/lib/ai.js
@@ -40,6 +40,15 @@ class ReplyError extends Error {}
 
 const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));
 
+// Cuts text to at most max UTF-16 units without splitting an emoji in half. A lone
+// half (surrogate) is still sent as JSON, but some APIs (DeepSeek) refuse to parse it.
+function clip(text, max) {
+  const s = String(text);
+  if (s.length <= max) return s;
+  const cut = s.slice(0, max);
+  return /[\uD800-\uDBFF]$/.test(cut) ? cut.slice(0, -1) : cut;
+}
+
 // Settings values (ai_provider, ai_base_url, …) -> a client config, filling the
 // gaps from the provider's preset.
 function configFrom(values = {}) {
@@ -88,7 +97,7 @@ function modelSummary(model, knownTags = []) {
   const size = modelSize(model);
   if (size) lines.push(`Size: ${size}`);
   if (model.tags && model.tags.length) lines.push(`Tags so far: ${model.tags.join(', ')}`);
-  if (model.description && model.description.trim()) lines.push(`Description so far: ${model.description.trim().slice(0, 800)}`);
+  if (model.description && model.description.trim()) lines.push(`Description so far: ${clip(model.description.trim(), 800)}`);
   if (knownTags.length) lines.push(`Tags already used in this library: ${knownTags.join(', ')}`);
   return lines.join('\n');
 }
@@ -108,6 +117,8 @@ function buildMessages(model, {
     + (describe ? DESCRIBE_PROMPT : '')
     + (suggestName ? NAME_PROMPT : '')
     + (suggestCollections ? COLLECTIONS_PROMPT : '');
+  // Stored names and descriptions may already hold a broken emoji; send a stand-in instead.
+  text = text.toWellFormed();
   const content = image
     ? [{ type: 'text', text }, { type: 'image_url', image_url: { url: image } }]
     : text;
@@ -118,12 +129,11 @@ function normalizeTags(value) {
   const list = Array.isArray(value) ? value : typeof value === 'string' ? value.split(',') : [];
   const tags = [];
   for (const raw of list) {
-    const tag = String(raw).toLowerCase()
+    const tag = clip(String(raw).toLowerCase()
       .replace(/^#+/, '')
       .replace(/[_\s]+/g, ' ')
       .replace(/[^\p{L}\p{N} +&'-]/gu, '')
-      .trim()
-      .slice(0, 40)
+      .trim(), 40)
       .trim();
     if (tag && !GENERIC_TAGS.has(tag) && !tags.includes(tag)) tags.push(tag);
   }
@@ -137,11 +147,10 @@ const stripQuotes = (s) => String(s).replace(/^["'“”‘’]+|["'“”‘’
 // written differently.
 function cleanName(value, currentName) {
   if (typeof value !== 'string') return null;
-  const name = stripQuotes(value)
+  const name = clip(stripQuotes(value)
     .replace(/\.(stl|3mf|obj|fbx|step|stp|3dm|gcode|zip|7z|rar)$/i, '')
     .replace(/\s+/g, ' ')
-    .trim()
-    .slice(0, 80)
+    .trim(), 80)
     .trim();
   return name && comparable(name) !== comparable(currentName) ? name : null;
 }
@@ -151,7 +160,7 @@ function normalizeCollections(value) {
   const list = Array.isArray(value) ? value : typeof value === 'string' ? value.split(',') : [];
   const names = [];
   for (const raw of list) {
-    const name = stripQuotes(raw).replace(/\s+/g, ' ').trim().slice(0, 60).trim();
+    const name = clip(stripQuotes(raw).replace(/\s+/g, ' ').trim(), 60).trim();
     if (name && !names.some((n) => comparable(n) === comparable(name))) names.push(name);
   }
   return names.slice(0, 3);
@@ -171,7 +180,7 @@ function parseReply(content, options = {}) {
   }
   if (!data || typeof data !== 'object') throw new ReplyError('The AI reply wasn’t the JSON asked for');
   const tags = describe ? normalizeTags(data.tags) : [];
-  const description = describe && typeof data.description === 'string' ? data.description.trim().slice(0, 600) : '';
+  const description = describe && typeof data.description === 'string' ? clip(data.description.trim(), 600) : '';
   if (describe && !tags.length && !description) throw new ReplyError('The AI reply had no tags or description');
   return {
     tags,
diff --git a/test/ai.test.js b/test/ai.test.js
index 4a59435..d4705f1 100644
--- a/test/ai.test.js
+++ b/test/ai.test.js
@@ -146,6 +146,23 @@ test('a reply that isn’t JSON is asked again once, and both answers count towa
   }
 });
 
+test('text sent to the AI never holds half an emoji', () => {
+  // The panda starts at unit 799, so a plain cut at 800 would split it.
+  const description = `${'a'.repeat(799)}🐼 red panda`;
+  const [, user] = ai.buildMessages({ name: 'Red panda', files: [], tags: [], description });
+  assert.ok(user.content.isWellFormed());
+  assert.ok(!user.content.includes('\uFFFD'), 'clipped before the emoji, not replaced');
+  assert.match(user.content, /Description so far: a{799}$/m);
+
+  // Text that's already broken in the library is made safe before it's sent.
+  const [, broken] = ai.buildMessages({ name: 'Bad \uD83D name', files: [], tags: ['ok'], description: '' }, { knownTags: ['tag\uDC3C'] });
+  assert.ok(broken.content.isWellFormed());
+
+  const reply = JSON.stringify({ name: `x${'🐼'.repeat(50)}`, tags: ['panda'], description: `x${'🐼'.repeat(400)}`, collections: [`x${'🐼'.repeat(40)}`] });
+  const parsed = ai.parseReply(reply, { currentName: 'Red panda', collections: true });
+  assert.ok(parsed.name.isWellFormed() && parsed.description.isWellFormed() && parsed.collections[0].isWellFormed());
+});
+
 test('a rejected key is fatal for a run; a bad reply is not', async () => {
   const provider = await fakeProvider([() => [401, { error: { message: 'Authentication Fails' } }]]);
   try {