diff --git a/server/src/routes/admin.ts b/server/src/routes/admin.ts
index e57a617..c092acd 100644
--- a/server/src/routes/admin.ts
+++ b/server/src/routes/admin.ts
@@ -4,6 +4,14 @@ import { businessDay, formatLocal, parseDbTime } from '../time.js';
 
 const SESSION_COOKIE = 'wutz_admin';
 
+// Generous ceiling for a single drink price or deposit amount — bounds a
+// typo (or a `2.5`/`"abc"` slipping past a missing check) from wrecking a
+// bar's pricing. See wutzcalc#12.
+const MAX_CENTS = 100_000_00; // 100,000 €
+function isValidCents(v: unknown): v is number {
+  return typeof v === 'number' && Number.isInteger(v) && v >= 0 && v <= MAX_CENTS;
+}
+
 function isAuthed(req: FastifyRequest): boolean {
   const expected = process.env.ADMIN_PASSWORD;
   if (!expected) return false;
@@ -50,8 +58,7 @@ export function registerAdminRoutes(app: FastifyInstance, db: DB) {
     async (req, reply) => {
       if (!requireAuth(req, reply)) return;
       const { name, price_cents } = req.body ?? ({} as any);
-      if (!name || !Number.isInteger(price_cents))
-        return reply.code(400).send({ error: 'invalid' });
+      if (!name || !isValidCents(price_cents)) return reply.code(400).send({ error: 'invalid' });
       const info = db
         .prepare('INSERT INTO drinks (name, price_cents) VALUES (?, ?)')
         .run(name, price_cents);
@@ -65,6 +72,9 @@ export function registerAdminRoutes(app: FastifyInstance, db: DB) {
       if (!requireAuth(req, reply)) return;
       const id = Number(req.params.id);
       const { name, price_cents, archived } = req.body ?? {};
+      if (price_cents !== undefined && !isValidCents(price_cents)) {
+        return reply.code(400).send({ error: 'invalid price_cents' });
+      }
       const sets: string[] = [];
       const args: any[] = [];
       if (name !== undefined) { sets.push('name = ?'); args.push(name); }
@@ -115,6 +125,9 @@ export function registerAdminRoutes(app: FastifyInstance, db: DB) {
       const name = req.body?.name?.trim();
       const pfand_cents = req.body?.pfand_cents ?? 0;
       if (!name) return reply.code(400).send({ error: 'name required' });
+      if (!isValidCents(pfand_cents)) {
+        return reply.code(400).send({ error: 'invalid pfand_cents' });
+      }
       try {
         const info = db
           .prepare('INSERT INTO bars (name, pfand_cents) VALUES (?, ?)')
@@ -135,6 +148,9 @@ export function registerAdminRoutes(app: FastifyInstance, db: DB) {
       if (!requireAuth(req, reply)) return;
       const id = Number(req.params.id);
       const { name, pfand_cents, drink_ids } = req.body ?? {};
+      if (pfand_cents !== undefined && !isValidCents(pfand_cents)) {
+        return reply.code(400).send({ error: 'invalid pfand_cents' });
+      }
       try {
         db.transaction(() => {
           if (name !== undefined) {
diff --git a/server/src/routes/public.ts b/server/src/routes/public.ts
index 96a4e53..b574116 100644
--- a/server/src/routes/public.ts
+++ b/server/src/routes/public.ts
@@ -37,10 +37,16 @@ export function registerPublicRoutes(app: FastifyInstance, db: DB) {
     return config;
   });
 
+  // Sane ceilings for money-adjacent quantities — generous for any real
+  // order/return, but bounded so a stuck button or a bad request can't post
+  // an absurd (or precision-losing) total. See wutzcalc#12.
+  const MAX_QTY_PER_LINE = 999;
+  const MAX_PFAND_RETURNS = 999;
+  const MAX_ITEMS_PER_TRANSACTION = 100;
+
   app.post<{ Body: CreateTransactionRequest }>('/api/transactions', async (req, reply) => {
     const body = req.body ?? ({} as CreateTransactionRequest);
     const { client_uuid, bar_id, crew, items } = body;
-    const pfand_returns = Math.max(0, Math.floor(body.pfand_returns ?? 0));
 
     if (!client_uuid || typeof client_uuid !== 'string') {
       return reply.code(400).send({ error: 'client_uuid required' });
@@ -51,6 +57,19 @@ export function registerPublicRoutes(app: FastifyInstance, db: DB) {
     if (!Array.isArray(items)) {
       return reply.code(400).send({ error: 'items required' });
     }
+    if (items.length > MAX_ITEMS_PER_TRANSACTION) {
+      return reply.code(400).send({ error: 'too many items' });
+    }
+
+    const rawPfandReturns = body.pfand_returns ?? 0;
+    if (!Number.isInteger(rawPfandReturns) || rawPfandReturns < 0) {
+      return reply.code(400).send({ error: 'pfand_returns must be a non-negative integer' });
+    }
+    if (rawPfandReturns > MAX_PFAND_RETURNS) {
+      return reply.code(400).send({ error: 'pfand_returns too large' });
+    }
+    const pfand_returns = rawPfandReturns;
+
     if (items.length === 0 && pfand_returns === 0) {
       return reply.code(400).send({ error: 'empty transaction' });
     }
@@ -87,7 +106,12 @@ export function registerPublicRoutes(app: FastifyInstance, db: DB) {
     }> = [];
 
     for (const item of items) {
-      if (!Number.isInteger(item.drink_id) || !Number.isInteger(item.qty) || item.qty <= 0) {
+      if (
+        !Number.isInteger(item.drink_id) ||
+        !Number.isInteger(item.qty) ||
+        item.qty <= 0 ||
+        item.qty > MAX_QTY_PER_LINE
+      ) {
         return reply.code(400).send({ error: 'invalid item' });
       }
       const drink = drinkStmt.get(bar_id, item.drink_id) as