Use client browser timezone instead of server timezone for agent tools

app/src/services/chatService.ts

@@ -227,7 +227,7 @@ class ChatService {
       }, 30000);
       this.pendingRequests.set(requestId, { resolve: resolve as any, reject, timer });
 
-      const payload: any = { type: 'send_message', message: content, requestId };
+      const payload: any = { type: 'send_message', message: content, requestId, timezone: Intl.DateTimeFormat().resolvedOptions().timeZone };
       if (conversationId) {
         // Defense-in-depth: validate conversationId format on the client side too
         if (!/^[a-zA-Z0-9_-]{1,64}$/.test(conversationId)) {

backend/src/agent/agent.ts

@@ -23,19 +23,19 @@ When the user asks to create, update, or delete events, use the corresponding to
 
 Always confirm what you're about to do before taking action. Be concise and helpful. All times to be displayed to the user must be in their local time always unless they specify otherwise.`;
 
-export async function createCalendarAgent(accessToken: string) {
+export async function createCalendarAgent(accessToken: string, timezone?: string) {
   const llm = createLLM();
 
   const tools = [
-    createGetCurrentDateTimeTool(),
+    createGetCurrentDateTimeTool(timezone),
     createListCalendarsTool(accessToken),
-    createListEventsTool(accessToken),
-    createSearchEventsTool(accessToken),
+    createListEventsTool(accessToken, timezone),
+    createSearchEventsTool(accessToken, timezone),
     createGetFreeBusyTool(accessToken),
-    createCreateEventTool(),
-    createUpdateEventTool(),
+    createCreateEventTool(timezone),
+    createUpdateEventTool(timezone),
     createDeleteEventTool(),
-    createDateTimeMathTool(),
+    createDateTimeMathTool(timezone),
   ];
 
   const agent = createReactAgent({

backend/src/agent/tools/createEventTool.ts

@@ -1,13 +1,13 @@
 import { tool } from '@langchain/core/tools';
 import { z } from 'zod';
 
-export function createCreateEventTool() {
+export function createCreateEventTool(clientTimezone?: string) {
   return tool(
     async (input) => {
       return JSON.stringify({
         pendingAction: true,
         actionType: 'create_event',
-        payload: input,
+        payload: { ...input, timeZone: input.timeZone || clientTimezone },
       });
     },
     {
@@ -20,6 +20,7 @@ export function createCreateEventTool() {
         calendarId: z.string().describe('Calendar ID. Use "primary" for default calendar.'),
         description: z.string().optional().describe('Event description'),
         location: z.string().optional().describe('Event location'),
+        timeZone: z.string().optional().describe('IANA timezone for the event (e.g. "America/New_York"). Defaults to user\'s browser timezone.'),
       }),
     }
   );

backend/src/agent/tools/dateTimeMathTool.ts

@@ -2,15 +2,18 @@ import { tool } from '@langchain/core/tools';
 import { z } from 'zod';
 import { DateTime, Duration } from 'luxon';
 
-export function createDateTimeMathTool() {
+export function createDateTimeMathTool(clientTimezone?: string) {
   return tool(
     async (input) => {
       const { operation } = input;
 
       switch (operation) {
         case 'add':
         case 'subtract': {
-          const dt = DateTime.fromISO(input.datetime!);
+          let dt = DateTime.fromISO(input.datetime!);
+          if (clientTimezone && !input.datetime!.match(/[+-]\d{2}:\d{2}$|Z$/)) {
+            dt = DateTime.fromISO(input.datetime!, { zone: clientTimezone });
+          }
           if (!dt.isValid) return JSON.stringify({ error: `Invalid datetime: ${input.datetime}` });
 
           const dur = Duration.fromObject({

backend/src/agent/tools/getCurrentDateTimeTool.ts

@@ -2,10 +2,12 @@ import { tool } from '@langchain/core/tools';
 import { z } from 'zod';
 import { DateTime } from 'luxon';
 
-export function createGetCurrentDateTimeTool() {
+export function createGetCurrentDateTimeTool(clientTimezone?: string) {
   return tool(
     async () => {
-      const now = DateTime.now();
+      const now = clientTimezone
+        ? DateTime.now().setZone(clientTimezone)
+        : DateTime.now();
 
       return JSON.stringify({
         date: now.toFormat('yyyy-MM-dd'),

backend/src/agent/tools/listEventsTool.ts

@@ -5,20 +5,20 @@ import { DateTime } from 'luxon';
 import { calendarService } from '../../services/calendar.service';
 import { CalendarEvent } from '../../types';
 
-function convertEventTimesToLocal(events: CalendarEvent[]): CalendarEvent[] {
-  const localZone = DateTime.now().zoneName;
+function convertEventTimesToLocal(events: CalendarEvent[], clientTimezone?: string): CalendarEvent[] {
+  const zone = clientTimezone || DateTime.now().zoneName;
   return events.map((event) => ({
     ...event,
     start: event.start?.dateTime
-      ? { ...event.start, dateTime: DateTime.fromISO(event.start.dateTime).setZone(localZone).toISO()! }
+      ? { ...event.start, dateTime: DateTime.fromISO(event.start.dateTime).setZone(zone).toISO()! }
       : event.start,
     end: event.end?.dateTime
-      ? { ...event.end, dateTime: DateTime.fromISO(event.end.dateTime).setZone(localZone).toISO()! }
+      ? { ...event.end, dateTime: DateTime.fromISO(event.end.dateTime).setZone(zone).toISO()! }
       : event.end,
   }));
 }
 
-export function createListEventsTool(accessToken: string) {
+export function createListEventsTool(accessToken: string, clientTimezone?: string) {
   const oauth2Client = new google.auth.OAuth2();
   oauth2Client.setCredentials({ access_token: accessToken });
 
@@ -28,7 +28,7 @@ export function createListEventsTool(accessToken: string) {
         timeMin: input.timeMin,
         timeMax: input.timeMax,
       });
-      return JSON.stringify(convertEventTimesToLocal(events));
+      return JSON.stringify(convertEventTimesToLocal(events, clientTimezone));
     },
     {
       name: 'list_events',

backend/src/agent/tools/searchEventsTool.ts

@@ -5,20 +5,20 @@ import { DateTime } from 'luxon';
 import { calendarService } from '../../services/calendar.service';
 import { CalendarEvent } from '../../types';
 
-function convertEventTimesToLocal(events: CalendarEvent[]): CalendarEvent[] {
-  const localZone = DateTime.now().zoneName;
+function convertEventTimesToLocal(events: CalendarEvent[], clientTimezone?: string): CalendarEvent[] {
+  const zone = clientTimezone || DateTime.now().zoneName;
   return events.map((event) => ({
     ...event,
     start: event.start?.dateTime
-      ? { ...event.start, dateTime: DateTime.fromISO(event.start.dateTime).setZone(localZone).toISO()! }
+      ? { ...event.start, dateTime: DateTime.fromISO(event.start.dateTime).setZone(zone).toISO()! }
       : event.start,
     end: event.end?.dateTime
-      ? { ...event.end, dateTime: DateTime.fromISO(event.end.dateTime).setZone(localZone).toISO()! }
+      ? { ...event.end, dateTime: DateTime.fromISO(event.end.dateTime).setZone(zone).toISO()! }
       : event.end,
   }));
 }
 
-export function createSearchEventsTool(accessToken: string) {
+export function createSearchEventsTool(accessToken: string, clientTimezone?: string) {
   const oauth2Client = new google.auth.OAuth2();
   oauth2Client.setCredentials({ access_token: accessToken });
 
@@ -33,7 +33,7 @@ export function createSearchEventsTool(accessToken: string) {
           timeMax: input.timeMax,
         }
       );
-      return JSON.stringify(convertEventTimesToLocal(events));
+      return JSON.stringify(convertEventTimesToLocal(events, clientTimezone));
     },
     {
       name: 'search_events',

backend/src/agent/tools/updateEventTool.ts

@@ -1,13 +1,13 @@
 import { tool } from '@langchain/core/tools';
 import { z } from 'zod';
 
-export function createUpdateEventTool() {
+export function createUpdateEventTool(clientTimezone?: string) {
   return tool(
     async (input) => {
       return JSON.stringify({
         pendingAction: true,
         actionType: 'update_event',
-        payload: input,
+        payload: { ...input, timeZone: input.timeZone || clientTimezone },
       });
     },
     {
@@ -21,6 +21,7 @@ export function createUpdateEventTool() {
         endDateTime: z.string().optional().describe('New end date/time in ISO 8601 format with timezone offset (e.g. "2026-01-30T10:00:00-05:00"). Use the utcOffset from get_current_datetime.'),
         description: z.string().optional().describe('New event description'),
         location: z.string().optional().describe('New event location'),
+        timeZone: z.string().optional().describe('IANA timezone for the event (e.g. "America/New_York"). Defaults to user\'s browser timezone.'),
       }),
     }
   );

backend/src/services/chat.service.ts

@@ -19,12 +19,13 @@ const MUTATING_ACTIONS: Record<string, ActionType> = {
  */
 async function callAgent(
   langchainMessages: BaseMessage[],
-  accessToken: string
+  accessToken: string,
+  timezone?: string
 ): Promise<{
   reply: string;
   toolCalls: { name: string; params: Record<string, any>; description: string }[];
 }> {
-  const agent = await createCalendarAgent(accessToken);
+  const agent = await createCalendarAgent(accessToken, timezone);
 
   const result = await agent.invoke({ messages: langchainMessages });
 
@@ -62,7 +63,8 @@ export class ChatService {
     userId: string,
     conversationId: string | null,
     message: string,
-    accessToken: string
+    accessToken: string,
+    timezone?: string
   ): Promise<ChatResponse> {
     // Load or create conversation
     let convId = conversationId;
@@ -92,7 +94,7 @@ export class ChatService {
     const langchainMessages = await chatHistory.getMessages();
 
     // Call agent
-    const agentResult = await callAgent(langchainMessages, accessToken);
+    const agentResult = await callAgent(langchainMessages, accessToken, timezone);
 
     // Save assistant reply (manual persistence — no duplication since agent
     // has no checkpointer and does not auto-persist)

backend/src/ws.ts

@@ -81,12 +81,16 @@ export function setupWebSocket(server: HttpServer): WebSocketServer {
         return;
       }
 
+      // Client timezone (IANA, e.g. "America/New_York")
+      const timezone = typeof parsed.timezone === 'string' ? parsed.timezone : undefined;
+
       try {
         const result = await chatService.sendMessage(
           userId,
           conversationId,
           message,
           accessToken,
+          timezone,
         );
         const data: any = { ...result };
         if (result.pendingAction) {