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+# Datetime Timezone Issue
+
+## Problem Description
+
+The API returns datetime strings without timezone suffixes, causing frontend JavaScript to parse them as local time instead of UTC time.
+
+### Example
+
+| Aspect | Value |
+|--------|-------|
+| Actual time (Beijing) | 2026-03-07 01:30 |
+| Backend returns | `2026-03-06T16:31:36.547762` (no timezone) |
+| Frontend displays | March 6, 16:31 |
+| Should display | March 7, 00:31 (UTC 16:31 + 8 hours) |
+
+### Root Cause
+
+- Backend stores UTC time in database as naive datetime (no timezone info)
+- FastAPI's `jsonable_encoder` serializes datetime as ISO 8601 **without timezone suffix**
+- JavaScript `new Date()` treats strings without 'Z' or timezone offset as **local time**
+
+```
+Backend intention: 2026-03-06T16:31:36Z (UTC)
+Actually returned: 2026-03-06T16:31:36.547762 (no timezone)
+JavaScript parses as: local time 16:31
+Should be: UTC 16:31 → Beijing time 00:31 (next day)
+```
+
+---
+
+## Frontend Solutions
+
+### Solution 1: Use dayjs UTC Parsing (Recommended)
+
+```typescript
+import dayjs from 'dayjs';
+import utc from 'dayjs/plugin/utc';
+import timezone from 'dayjs/plugin/timezone';
+
+dayjs.extend(utc);
+dayjs.extend(timezone);
+
+// Parse naive datetime as UTC
+const createdAt = '2026-03-06T16:31:36.547762';
+const date = dayjs.utc(createdAt).tz('Asia/Shanghai');
+console.log(date.format('YYYY-MM-DD HH:mm')); // 2026-03-07 00:31
+```
+
+### Solution 2: Add 'Z' Suffix Manually
+
+```typescript
+// Utility function to normalize API dates
+function parseAPIDate(dateStr: string): Date {
+  // Add 'Z' suffix if no timezone info present
+  const normalized = dateStr.includes('Z') || dateStr.includes('+')
+    ? dateStr
+    : `${dateStr}Z`;
+  return new Date(normalized);
+}
+
+// Usage
+const date = parseAPIDate('2026-03-06T16:31:36.547762');
+console.log(date.toLocaleString('zh-CN', { timeZone: 'Asia/Shanghai' }));
+```
+
+### Solution 3: Global Axios Interceptor (Most Thorough)
+
+```typescript
+import axios from 'axios';
+
+api.interceptors.response.use((response) => {
+  // Recursively normalize all date fields
+  function normalizeDates(obj: any): any {
+    // Match ISO 8601 datetime pattern without timezone
+    if (typeof obj === 'string' && /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}/.test(obj)) {
+      return obj.includes('Z') || obj.includes('+') ? obj : `${obj}Z`;
+    }
+    if (Array.isArray(obj)) {
+      return obj.map(normalizeDates);
+    }
+    if (obj && typeof obj === 'object') {
+      return Object.fromEntries(
+        Object.entries(obj).map(([k, v]) => [k, normalizeDates(v)])
+      );
+    }
+    return obj;
+  }
+
+  response.data = normalizeDates(response.data);
+  return response;
+});
+```
+
+---
+
+## Backend Context
+
+### Current Implementation
+
+**File**: `gns3server/api/server.py:58-64`
+
+```python
+application = FastAPI(
+    title="GNS3 controller API",
+    description="This page describes the public controller API for GNS3",
+    version="v3",
+    docs_url=None,
+    redoc_url=None
+)
+```
+
+**File**: `gns3server/db/models/base.py`
+
+```python
+from fastapi.encoders import jsonable_encoder
+
+class Base:
+    def asjson(self):
+        return jsonable_encoder(self.asdict())
+```
+
+### Datetime Flow
+
+1. Database stores naive datetime (no timezone)
+2. FastAPI uses `jsonable_encoder` to serialize
+3. Output format: `YYYY-MM-DDTHH:MM:SS.ffffff` (no 'Z' suffix)
+4. JavaScript interprets as local time
+
+### Affected Fields
+
+- `created_at`
+- `updated_at`
+- `last_login`
+- Any other datetime fields in API responses
+
+---
+
+## Testing Checklist
+
+- [ ] Verify datetime displays correctly in Beijing timezone (UTC+8)
+- [ ] Test with other timezones (e.g., UTC-5, UTC+0)
+- [ ] Check daylight saving time transitions (if applicable)
+- [ ] Verify datetime input/insertion still works correctly
+
+---
+
+## Related Files
+
+- Backend: `gns3server/api/server.py`
+- Backend: `gns3server/db/models/base.py`
+- Schemas: `gns3server/schemas/controller/base.py`