diff --git a/src/app.module.ts b/src/app.module.ts
index 41f8cb9..680b687 100644
--- a/src/app.module.ts
+++ b/src/app.module.ts
@@ -21,6 +21,7 @@ import { RulesEngineModule } from './rules-engine/rules-engine.module';
 import { ConfigThemeModule } from './config/config-theme.module';
 import { WidgetModule } from './widget/widget.module';
 import { TeamModule } from './team/team.module';
+import { MasterdataModule } from './masterdata/masterdata.module';
 import { TelephonyRegistrationService } from './telephony-registration.service';
 
 @Module({
@@ -49,6 +50,7 @@ import { TelephonyRegistrationService } from './telephony-registration.service';
         ConfigThemeModule,
         WidgetModule,
         TeamModule,
+        MasterdataModule,
     ],
     providers: [TelephonyRegistrationService],
 })
diff --git a/src/masterdata/masterdata.controller.ts b/src/masterdata/masterdata.controller.ts
new file mode 100644
index 0000000..9bfaf2a
--- /dev/null
+++ b/src/masterdata/masterdata.controller.ts
@@ -0,0 +1,45 @@
+import { Controller, Get, Query, Logger } from '@nestjs/common';
+import { MasterdataService } from './masterdata.service';
+
+@Controller('api/masterdata')
+export class MasterdataController {
+    private readonly logger = new Logger(MasterdataController.name);
+
+    constructor(private masterdata: MasterdataService) {}
+
+    @Get('departments')
+    async departments() {
+        return this.masterdata.getDepartments();
+    }
+
+    @Get('doctors')
+    async doctors() {
+        return this.masterdata.getDoctors();
+    }
+
+    @Get('clinics')
+    async clinics() {
+        return this.masterdata.getClinics();
+    }
+
+    // Available time slots for a doctor on a given date.
+    // Computed from DoctorVisitSlot entities (doctor × clinic × dayOfWeek).
+    // Returns 30-min slots within the doctor's visiting window for that day.
+    //
+    // GET /api/masterdata/slots?doctorId=xxx&date=2026-04-15
+    @Get('slots')
+    async slots(
+        @Query('doctorId') doctorId: string,
+        @Query('date') date: string,
+    ) {
+        if (!doctorId || !date) return [];
+        return this.masterdata.getAvailableSlots(doctorId, date);
+    }
+
+    // Force cache refresh (admin use)
+    @Get('refresh')
+    async refresh() {
+        await this.masterdata.invalidateAll();
+        return { refreshed: true };
+    }
+}
diff --git a/src/masterdata/masterdata.module.ts b/src/masterdata/masterdata.module.ts
new file mode 100644
index 0000000..8e76bf5
--- /dev/null
+++ b/src/masterdata/masterdata.module.ts
@@ -0,0 +1,13 @@
+import { Module } from '@nestjs/common';
+import { PlatformModule } from '../platform/platform.module';
+import { AuthModule } from '../auth/auth.module';
+import { MasterdataController } from './masterdata.controller';
+import { MasterdataService } from './masterdata.service';
+
+@Module({
+    imports: [PlatformModule, AuthModule],
+    controllers: [MasterdataController],
+    providers: [MasterdataService],
+    exports: [MasterdataService],
+})
+export class MasterdataModule {}
diff --git a/src/masterdata/masterdata.service.ts b/src/masterdata/masterdata.service.ts
new file mode 100644
index 0000000..d64f63c
--- /dev/null
+++ b/src/masterdata/masterdata.service.ts
@@ -0,0 +1,183 @@
+import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import { PlatformGraphqlService } from '../platform/platform-graphql.service';
+import { SessionService } from '../auth/session.service';
+
+// Master data: cached lookups for departments, doctors, clinics.
+// Fetched from the platform on first request, cached in Redis with TTL.
+// Frontend dropdowns use these instead of direct GraphQL queries.
+
+const CACHE_TTL = 300; // 5 minutes
+const KEY_DEPARTMENTS = 'masterdata:departments';
+const KEY_DOCTORS = 'masterdata:doctors';
+const KEY_CLINICS = 'masterdata:clinics';
+
+@Injectable()
+export class MasterdataService implements OnModuleInit {
+    private readonly logger = new Logger(MasterdataService.name);
+    private readonly apiKey: string;
+
+    constructor(
+        private config: ConfigService,
+        private platform: PlatformGraphqlService,
+        private cache: SessionService,
+    ) {
+        this.apiKey = this.config.get<string>('platform.apiKey') ?? process.env.PLATFORM_API_KEY ?? '';
+    }
+
+    async onModuleInit() {
+        // Warm cache on startup
+        try {
+            await this.getDepartments();
+            await this.getDoctors();
+            await this.getClinics();
+            this.logger.log('Master data cache warmed');
+        } catch (err: any) {
+            this.logger.warn(`Cache warm failed: ${err.message}`);
+        }
+    }
+
+    async getDepartments(): Promise<string[]> {
+        const cached = await this.cache.getCache(KEY_DEPARTMENTS);
+        if (cached) return JSON.parse(cached);
+
+        const auth = `Bearer ${this.apiKey}`;
+        const data = await this.platform.queryWithAuth<any>(
+            `{ doctors(first: 500) { edges { node { department } } } }`,
+            undefined, auth,
+        );
+
+        const departments = Array.from(new Set(
+            data.doctors.edges
+                .map((e: any) => e.node.department)
+                .filter((d: string) => d && d.trim()),
+        )).sort() as string[];
+
+        await this.cache.setCache(KEY_DEPARTMENTS, JSON.stringify(departments), CACHE_TTL);
+        this.logger.log(`Cached ${departments.length} departments`);
+        return departments;
+    }
+
+    async getDoctors(): Promise<Array<{ id: string; name: string; department: string; qualifications: string }>> {
+        const cached = await this.cache.getCache(KEY_DOCTORS);
+        if (cached) return JSON.parse(cached);
+
+        const auth = `Bearer ${this.apiKey}`;
+        const data = await this.platform.queryWithAuth<any>(
+            `{ doctors(first: 500) { edges { node {
+                id name department qualifications specialty active
+                fullName { firstName lastName }
+            } } } }`,
+            undefined, auth,
+        );
+
+        const doctors = data.doctors.edges
+            .map((e: any) => ({
+                id: e.node.id,
+                name: e.node.name ?? `${e.node.fullName?.firstName ?? ''} ${e.node.fullName?.lastName ?? ''}`.trim(),
+                department: e.node.department ?? '',
+                qualifications: e.node.qualifications ?? '',
+                specialty: e.node.specialty ?? '',
+                active: e.node.active ?? true,
+            }))
+            .filter((d: any) => d.active !== false);
+
+        await this.cache.setCache(KEY_DOCTORS, JSON.stringify(doctors), CACHE_TTL);
+        this.logger.log(`Cached ${doctors.length} doctors`);
+        return doctors;
+    }
+
+    async getClinics(): Promise<Array<{ id: string; name: string; phone: string; address: string; opensAt: string; closesAt: string }>> {
+        const cached = await this.cache.getCache(KEY_CLINICS);
+        if (cached) return JSON.parse(cached);
+
+        const auth = `Bearer ${this.apiKey}`;
+        const data = await this.platform.queryWithAuth<any>(
+            `{ clinics(first: 50) { edges { node {
+                id clinicName status opensAt closesAt
+                phone { primaryPhoneNumber }
+                addressCustom { addressCity addressState }
+            } } } }`,
+            undefined, auth,
+        );
+
+        const clinics = data.clinics.edges
+            .filter((e: any) => e.node.status !== 'INACTIVE')
+            .map((e: any) => ({
+                id: e.node.id,
+                name: e.node.clinicName ?? '',
+                phone: e.node.phone?.primaryPhoneNumber ?? '',
+                opensAt: e.node.opensAt ?? '08:00',
+                closesAt: e.node.closesAt ?? '20:00',
+                address: [e.node.addressCustom?.addressCity, e.node.addressCustom?.addressState].filter(Boolean).join(', '),
+            }));
+
+        await this.cache.setCache(KEY_CLINICS, JSON.stringify(clinics), CACHE_TTL);
+        this.logger.log(`Cached ${clinics.length} clinics`);
+        return clinics;
+    }
+
+    // Available time slots for a doctor on a given date.
+    // Reads DoctorVisitSlot entities for the matching dayOfWeek,
+    // then generates 30-min slots within each visiting window.
+    async getAvailableSlots(doctorId: string, date: string): Promise<Array<{ time: string; label: string; clinicId: string; clinicName: string }>> {
+        const dayOfWeek = new Date(date).toLocaleDateString('en-US', { weekday: 'long' }).toUpperCase();
+        const cacheKey = `masterdata:slots:${doctorId}:${dayOfWeek}`;
+
+        const cached = await this.cache.getCache(cacheKey);
+        if (cached) return JSON.parse(cached);
+
+        const auth = `Bearer ${this.apiKey}`;
+        const data = await this.platform.queryWithAuth<any>(
+            `{ doctorVisitSlots(first: 100, filter: { doctorId: { eq: "${doctorId}" }, dayOfWeek: { eq: ${dayOfWeek} } }) {
+                edges { node { id startTime endTime clinic { id clinicName } } }
+            } }`,
+            undefined, auth,
+        );
+
+        const slots: Array<{ time: string; label: string; clinicId: string; clinicName: string }> = [];
+
+        for (const edge of data.doctorVisitSlots?.edges ?? []) {
+            const node = edge.node;
+            const clinicId = node.clinic?.id ?? '';
+            const clinicName = node.clinic?.clinicName ?? '';
+            const startTime = node.startTime ?? '09:00';
+            const endTime = node.endTime ?? '17:00';
+
+            // Generate 30-min slots within visiting window
+            const [startH, startM] = startTime.split(':').map(Number);
+            const [endH, endM] = endTime.split(':').map(Number);
+            let h = startH, m = startM ?? 0;
+            const endMin = endH * 60 + (endM ?? 0);
+
+            while (h * 60 + m < endMin) {
+                const hh = h.toString().padStart(2, '0');
+                const mm = m.toString().padStart(2, '0');
+                const ampm = h < 12 ? 'AM' : 'PM';
+                const displayH = h === 0 ? 12 : h > 12 ? h - 12 : h;
+                slots.push({
+                    time: `${hh}:${mm}`,
+                    label: `${displayH}:${mm.toString().padStart(2, '0')} ${ampm} — ${clinicName}`,
+                    clinicId,
+                    clinicName,
+                });
+                m += 30;
+                if (m >= 60) { h++; m = 0; }
+            }
+        }
+
+        // Sort by time
+        slots.sort((a, b) => a.time.localeCompare(b.time));
+
+        await this.cache.setCache(cacheKey, JSON.stringify(slots), CACHE_TTL);
+        this.logger.log(`Generated ${slots.length} slots for doctor ${doctorId} on ${dayOfWeek}`);
+        return slots;
+    }
+
+    async invalidateAll(): Promise<void> {
+        await this.cache.setCache(KEY_DEPARTMENTS, '', 1);
+        await this.cache.setCache(KEY_DOCTORS, '', 1);
+        await this.cache.setCache(KEY_CLINICS, '', 1);
+        this.logger.log('Master data cache invalidated');
+    }
+}