diff --git a/.replit b/.replit
index 90b1d94..4827ed6 100644
--- a/.replit
+++ b/.replit
@@ -19,6 +19,10 @@ externalPort = 80
 localPort = 33035
 externalPort = 3001
 
+[[ports]]
+localPort = 37831
+externalPort = 5173
+
 [[ports]]
 localPort = 41343
 externalPort = 3000
diff --git a/replit.md b/replit.md
index 6d491d3..1403953 100644
--- a/replit.md
+++ b/replit.md
@@ -10,6 +10,43 @@ VigilanzaTurni is a professional 24/7 shift management system designed for secur
 - Focus su efficienza e densità informativa
 - **Testing**: Tutti i test vengono eseguiti ESCLUSIVAMENTE sul server esterno (vt.alfacom.it) con autenticazione locale (non Replit Auth)
 
+## ⚠️ CRITICAL: Date/Timezone Handling Rules
+**PROBLEMA RICORRENTE**: Quando si assegna una guardia per il giorno X, appare assegnata al giorno X±1 a causa di conversioni timezone.
+
+**REGOLE OBBLIGATORIE** per evitare questo bug:
+
+1. **MAI usare `parseISO()` su date YYYY-MM-DD**
+   - ❌ SBAGLIATO: `const date = parseISO("2025-10-20")` → converte in UTC causando shift
+   - ✅ CORRETTO: `const [y, m, d] = "2025-10-20".split("-").map(Number); const date = new Date(y, m-1, d)`
+
+2. **Costruire Date da componenti, NON da stringhe ISO**
+   ```typescript
+   // ✅ CORRETTO - date components (no timezone conversion)
+   const [year, month, day] = startDate.split("-").map(Number);
+   const shiftDate = new Date(year, month - 1, day);
+   const shiftStart = new Date(year, month - 1, day, startHour, startMin, 0, 0);
+   
+   // ❌ SBAGLIATO - parseISO o new Date(string ISO)
+   const date = parseISO(startDate); // converte in UTC!
+   const date = new Date("2025-10-20"); // timezone-dependent!
+   ```
+
+3. **Validazione date: usare regex, NON parseISO**
+   ```typescript
+   // ✅ CORRETTO
+   const dateRegex = /^\d{4}-\d{2}-\d{2}$/;
+   if (!dateRegex.test(dateStr)) { /* invalid */ }
+   
+   // ❌ SBAGLIATO
+   const parsed = parseISO(dateStr);
+   if (!isValid(parsed)) { /* invalid */ }
+   ```
+
+4. **File da verificare sempre**: `server/routes.ts` - tutte le route che ricevono date dal frontend
+5. **Testare sempre**: Assegnare guardia giorno X → verificare appaia nel giorno X (non X±1)
+
+**RIFERIMENTI FIX**: Vedere commit "Fix timezone bug in shift creation" - linee 1148-1184, 615-621, 753-759 in server/routes.ts
+
 ## System Architecture
 
 ### Stack Tecnologico
diff --git a/server/routes.ts b/server/routes.ts
index 7ae8682..2dc6cad 100644
--- a/server/routes.ts
+++ b/server/routes.ts
@@ -609,13 +609,13 @@ export async function registerRoutes(app: Express): Promise<Server> {
       const rawDateStr = req.query.date as string || format(new Date(), "yyyy-MM-dd");
       const normalizedDateStr = rawDateStr.split("/")[0]; // Prende solo la prima parte se c'è uno slash
       
-      // Valida la data
-      const parsedDate = parseISO(normalizedDateStr);
-      if (!isValid(parsedDate)) {
+      // TIMEZONE FIX: Valida formato senza parseISO per evitare shift timezone
+      const dateRegex = /^\d{4}-\d{2}-\d{2}$/;
+      if (!dateRegex.test(normalizedDateStr)) {
         return res.status(400).json({ message: "Invalid date format. Use yyyy-MM-dd" });
       }
       
-      const dateStr = format(parsedDate, "yyyy-MM-dd");
+      const dateStr = normalizedDateStr;
       
       // Ottieni location dalla query (default: roccapiemonte)
       const location = req.query.location as string || "roccapiemonte";
@@ -748,13 +748,13 @@ export async function registerRoutes(app: Express): Promise<Server> {
       const rawDateStr = req.query.date as string || format(new Date(), "yyyy-MM-dd");
       const normalizedDateStr = rawDateStr.split("/")[0]; // Prende solo la prima parte se c'è uno slash
       
-      // Valida la data
-      const parsedDate = parseISO(normalizedDateStr);
-      if (!isValid(parsedDate)) {
+      // TIMEZONE FIX: Valida formato senza parseISO per evitare shift timezone
+      const dateRegex = /^\d{4}-\d{2}-\d{2}$/;
+      if (!dateRegex.test(normalizedDateStr)) {
         return res.status(400).json({ message: "Invalid date format. Use yyyy-MM-dd" });
       }
       
-      const dateStr = format(parsedDate, "yyyy-MM-dd");
+      const dateStr = normalizedDateStr;
       
       // Ottieni location dalla query (default: roccapiemonte)
       const location = req.query.location as string || "roccapiemonte";
@@ -1142,9 +1142,12 @@ export async function registerRoutes(app: Express): Promise<Server> {
       }
       
       // Pre-validate all dates are within contract period
-      const startDateParsed = parseISO(startDate);
+      // TIMEZONE FIX: Parse date as YYYY-MM-DD components to avoid timezone shifts
+      const [year, month, day] = startDate.split("-").map(Number);
+      
       for (let dayOffset = 0; dayOffset < days; dayOffset++) {
-        const shiftDate = addDays(startDateParsed, dayOffset);
+        // Create date using local timezone components (no UTC conversion)
+        const shiftDate = new Date(year, month - 1, day + dayOffset);
         const shiftDateStr = format(shiftDate, "yyyy-MM-dd");
         
         if (site.contractStartDate && site.contractEndDate) {
@@ -1163,7 +1166,8 @@ export async function registerRoutes(app: Express): Promise<Server> {
         const createdShiftsInTx = [];
         
         for (let dayOffset = 0; dayOffset < days; dayOffset++) {
-          const shiftDate = addDays(startDateParsed, dayOffset);
+          // TIMEZONE FIX: Build date from components to maintain correct day
+          const shiftDate = new Date(year, month - 1, day + dayOffset);
           
           // Use site service schedule or default 24h
           const serviceStart = site.serviceStartTime || "00:00";
@@ -1172,11 +1176,9 @@ export async function registerRoutes(app: Express): Promise<Server> {
           const [startHour, startMin] = serviceStart.split(":").map(Number);
           const [endHour, endMin] = serviceEnd.split(":").map(Number);
           
-          const shiftStart = new Date(shiftDate);
-          shiftStart.setHours(startHour, startMin, 0, 0);
-          
-          const shiftEnd = new Date(shiftDate);
-          shiftEnd.setHours(endHour, endMin, 0, 0);
+          // Build timestamps using date components (no timezone conversion)
+          const shiftStart = new Date(year, month - 1, day + dayOffset, startHour, startMin, 0, 0);
+          const shiftEnd = new Date(year, month - 1, day + dayOffset, endHour, endMin, 0, 0);
           
           // If service ends before it starts, it spans midnight (add 1 day to end)
           if (shiftEnd <= shiftStart) {