diff --git a/services/spamshield/src/circuit-breaker/circuit-breaker.ts b/services/spamshield/src/circuit-breaker/circuit-breaker.ts
new file mode 100644
index 0000000..60604d8
--- /dev/null
+++ b/services/spamshield/src/circuit-breaker/circuit-breaker.ts
@@ -0,0 +1,173 @@
+export type CircuitState = 'CLOSED' | 'OPEN' | 'HALF_OPEN';
+
+export interface CircuitBreakerMetrics {
+  state: CircuitState;
+  failureCount: number;
+  successCount: number;
+  lastFailureTime: Date | null;
+  lastSuccessTime: Date | null;
+  stateChangedAt: Date | null;
+  totalExecutions: number;
+  totalFailures: number;
+  totalSuccesses: number;
+}
+
+export interface CircuitBreakerOptions {
+  failureThreshold?: number;
+  successThreshold?: number;
+  timeout?: number;
+  onStateChange?: (state: CircuitState, previousState: CircuitState) => void;
+}
+
+const DEFAULT_FAILURE_THRESHOLD = 5;
+const DEFAULT_SUCCESS_THRESHOLD = 3;
+const DEFAULT_TIMEOUT_MS = 60000;
+
+export class CircuitBreakerError extends Error {
+  public readonly state: CircuitState;
+
+  constructor(message: string, state: CircuitState) {
+    super(message);
+    this.name = 'CircuitBreakerError';
+    this.state = state;
+  }
+}
+
+export class CircuitBreaker {
+  private state: CircuitState = 'CLOSED';
+  private failureCount = 0;
+  private successCount = 0;
+  private lastFailureTime: Date | null = null;
+  private lastSuccessTime: Date | null = null;
+  private stateChangedAt: Date | null = null;
+  private totalExecutions = 0;
+  private totalFailures = 0;
+  private totalSuccesses = 0;
+
+  private readonly failureThreshold: number;
+  private readonly successThreshold: number;
+  private readonly timeout: number;
+  private readonly onStateChange?: (state: CircuitState, previousState: CircuitState) => void;
+
+  constructor(options?: CircuitBreakerOptions) {
+    this.failureThreshold = options?.failureThreshold ?? DEFAULT_FAILURE_THRESHOLD;
+    this.successThreshold = options?.successThreshold ?? DEFAULT_SUCCESS_THRESHOLD;
+    this.timeout = options?.timeout ?? DEFAULT_TIMEOUT_MS;
+    this.onStateChange = options?.onStateChange;
+    this.stateChangedAt = new Date();
+  }
+
+  public getState(): CircuitState {
+    if (this.state === 'OPEN') {
+      const elapsed = Date.now() - this.lastFailureTime!.getTime();
+      if (elapsed >= this.timeout) {
+        this.transitionTo('HALF_OPEN');
+      }
+    }
+    return this.state;
+  }
+
+  public async execute<T>(
+    fn: () => Promise<T>,
+    fallback?: () => T | Promise<T>
+  ): Promise<T> {
+    this.totalExecutions++;
+    const currentState = this.getState();
+
+    try {
+      let result: T;
+
+      if (currentState === 'OPEN') {
+        throw new CircuitBreakerError(
+          `Circuit is OPEN. Failures: ${this.failureCount}/${this.failureThreshold}`,
+          this.state
+        );
+      }
+
+      result = await fn();
+      this.recordSuccess();
+      return result;
+    } catch (error) {
+      this.recordFailure();
+
+      if (fallback) {
+        try {
+          return fallback();
+        } catch (fallbackError) {
+          throw error;
+        }
+      }
+
+      throw error;
+    }
+  }
+
+  public getMetrics(): CircuitBreakerMetrics {
+    return {
+      state: this.getState(),
+      failureCount: this.failureCount,
+      successCount: this.successCount,
+      lastFailureTime: this.lastFailureTime,
+      lastSuccessTime: this.lastSuccessTime,
+      stateChangedAt: this.stateChangedAt,
+      totalExecutions: this.totalExecutions,
+      totalFailures: this.totalFailures,
+      totalSuccesses: this.totalSuccesses,
+    };
+  }
+
+  public reset(): void {
+    const previousState = this.state;
+    this.state = 'CLOSED';
+    this.failureCount = 0;
+    this.successCount = 0;
+    this.lastFailureTime = null;
+    this.lastSuccessTime = null;
+    this.stateChangedAt = new Date();
+    if (previousState !== 'CLOSED') {
+      this.emitStateChange('CLOSED', previousState);
+    }
+  }
+
+  private recordSuccess(): void {
+    this.lastSuccessTime = new Date();
+    this.totalSuccesses++;
+
+    if (this.state === 'HALF_OPEN') {
+      this.successCount++;
+      if (this.successCount >= this.successThreshold) {
+        this.transitionTo('CLOSED');
+        this.failureCount = 0;
+        this.successCount = 0;
+      }
+    }
+  }
+
+  private recordFailure(): void {
+    this.lastFailureTime = new Date();
+    this.totalFailures++;
+    this.failureCount++;
+
+    if (this.state === 'HALF_OPEN') {
+      this.transitionTo('OPEN');
+    } else if (this.state === 'CLOSED' && this.failureCount >= this.failureThreshold) {
+      this.transitionTo('OPEN');
+    }
+  }
+
+  private transitionTo(newState: CircuitState): void {
+    const previousState = this.state;
+    this.state = newState;
+    this.stateChangedAt = new Date();
+    if (newState === 'CLOSED') {
+      this.successCount = 0;
+    }
+    this.emitStateChange(newState, previousState);
+  }
+
+  private emitStateChange(newState: CircuitState, previousState: CircuitState): void {
+    if (this.onStateChange && newState !== previousState) {
+      this.onStateChange(newState, previousState);
+    }
+  }
+}
diff --git a/services/spamshield/src/circuit-breaker/index.ts b/services/spamshield/src/circuit-breaker/index.ts
new file mode 100644
index 0000000..6465e15
--- /dev/null
+++ b/services/spamshield/src/circuit-breaker/index.ts
@@ -0,0 +1,2 @@
+export { CircuitBreaker, CircuitBreakerError } from './circuit-breaker';
+export type { CircuitState, CircuitBreakerMetrics, CircuitBreakerOptions } from './circuit-breaker';
diff --git a/services/spamshield/src/index.ts b/services/spamshield/src/index.ts
new file mode 100644
index 0000000..e01cb95
--- /dev/null
+++ b/services/spamshield/src/index.ts
@@ -0,0 +1,5 @@
+export { SpamShieldService } from './services/spamshield.service';
+export type { ReputationResult, CircuitMetrics } from './services/spamshield.service';
+export { spamRateLimits, spamFeatureFlags, spamConfig } from './config/spamshield.config';
+export { CircuitBreaker, CircuitBreakerError } from './circuit-breaker';
+export type { CircuitState, CircuitBreakerMetrics, CircuitBreakerOptions } from './circuit-breaker';
diff --git a/services/spamshield/src/services/spamshield.service.ts b/services/spamshield/src/services/spamshield.service.ts
new file mode 100644
index 0000000..93a961c
--- /dev/null
+++ b/services/spamshield/src/services/spamshield.service.ts
@@ -0,0 +1,285 @@
+import { PrismaClient, SpamFeedback, SpamRule, SpamAuditLog } from '@prisma/client';
+import { FieldEncryptionService } from '@shieldai/db';
+import { spamConfig, spamFeatureFlags } from '../config/spamshield.config';
+import { CircuitBreaker, CircuitBreakerError, CircuitState, CircuitBreakerMetrics } from '../circuit-breaker';
+
+const prisma = new PrismaClient() as PrismaClient & {
+  spamFeedback: {
+    create: (data: { data: SpamFeedback }) => Promise<SpamFeedback>;
+  };
+  spamRule: {
+    findMany: (args: { where: { isActive: boolean } }) => Promise<SpamRule[]>;
+  };
+  spamAuditLog: {
+    create: (data: { data: SpamAuditLog }) => Promise<SpamAuditLog>;
+  };
+};
+
+interface InitializationLock {
+  promise: Promise<void>;
+  resolved: boolean;
+}
+
+export interface ReputationResult {
+  score: number;
+  isSpam: boolean;
+  source: 'hiya' | 'truecaller' | 'combined' | 'fallback';
+  hiyaScore?: number;
+  truecallerScore?: number;
+}
+
+export interface CircuitMetrics {
+  hiya: CircuitBreakerMetrics;
+  truecaller: CircuitBreakerMetrics;
+}
+
+export class SpamShieldService {
+  private static instance: SpamShieldService;
+  private initLock: InitializationLock | null = null;
+  private hiyaBreaker: CircuitBreaker = new CircuitBreaker({
+    failureThreshold: spamConfig.circuitBreakerThreshold,
+    timeout: spamConfig.circuitBreakerTimeout,
+  });
+  private truecallerBreaker: CircuitBreaker = new CircuitBreaker({
+    failureThreshold: spamConfig.circuitBreakerThreshold,
+    timeout: spamConfig.circuitBreakerTimeout,
+  });
+
+  private constructor() {}
+
+  static getInstance(): SpamShieldService {
+    if (!SpamShieldService.instance) {
+      SpamShieldService.instance = new SpamShieldService();
+    }
+    return SpamShieldService.instance;
+  }
+
+  async initialize(): Promise<void> {
+    if (this.initLock?.resolved) return;
+
+    if (!this.initLock) {
+      this.initLock = {
+        promise: this._initialize(),
+        resolved: false,
+      };
+    }
+
+    await this.initLock.promise;
+  }
+
+  private async _initialize(): Promise<void> {
+    this.hiyaBreaker = new CircuitBreaker({
+      failureThreshold: spamConfig.circuitBreakerThreshold,
+      timeout: spamConfig.circuitBreakerTimeout,
+      onStateChange: (state: CircuitState, previous: CircuitState) => {
+        console.log(`[SpamShield] Hiya circuit: ${previous} -> ${state}`);
+      },
+    });
+    this.truecallerBreaker = new CircuitBreaker({
+      failureThreshold: spamConfig.circuitBreakerThreshold,
+      timeout: spamConfig.circuitBreakerTimeout,
+      onStateChange: (state: CircuitState, previous: CircuitState) => {
+        console.log(`[SpamShield] Truecaller circuit: ${previous} -> ${state}`);
+      },
+    });
+    this.initLock!.resolved = true;
+  }
+
+  async checkReputation(phoneNumber: string): Promise<ReputationResult> {
+    const validated = this.validatePhoneNumber(phoneNumber);
+
+    const results = await Promise.allSettled([
+      this.fetchHiyaReputation(validated),
+      this.fetchTruecallerReputation(validated),
+    ]);
+
+    const hiyaResult = results[0];
+    const truecallerResult = results[1];
+
+    const hiyaScore = hiyaResult.status === 'fulfilled' ? hiyaResult.value : undefined;
+    const truecallerScore = truecallerResult.status === 'fulfilled' ? truecallerResult.value : undefined;
+
+    if (hiyaScore !== undefined && truecallerScore !== undefined) {
+      const combinedScore = (hiyaScore + truecallerScore) / 2;
+      const isSpam = combinedScore > spamConfig.defaultConfidenceThreshold;
+      return {
+        score: combinedScore,
+        isSpam,
+        source: 'combined',
+        hiyaScore,
+        truecallerScore,
+      };
+    }
+
+    if (hiyaScore !== undefined) {
+      return {
+        score: hiyaScore,
+        isSpam: hiyaScore > spamConfig.defaultConfidenceThreshold,
+        source: 'hiya',
+        hiyaScore,
+      };
+    }
+
+    if (truecallerScore !== undefined) {
+      return {
+        score: truecallerScore,
+        isSpam: truecallerScore > spamConfig.defaultConfidenceThreshold,
+        source: 'truecaller',
+        truecallerScore,
+      };
+    }
+
+    return {
+      score: 0,
+      isSpam: false,
+      source: 'fallback',
+    };
+  }
+
+  async analyzeCall(phoneNumber: string, callTimestamp: Date): Promise<{
+    decision: 'BLOCK' | 'FLAG' | 'ALLOW';
+    confidence: number;
+    ruleMatches: string[];
+  }> {
+    const validated = this.validatePhoneNumber(phoneNumber);
+    const rules = await this.getActiveRules();
+
+    const ruleMatches: string[] = [];
+    let confidence = 0;
+
+    for (const rule of rules) {
+      const pattern = new RegExp(rule.pattern);
+      if (pattern.test(validated)) {
+        ruleMatches.push(rule.id);
+        confidence += 0.2;
+      }
+    }
+
+    confidence = Math.min(confidence, 1.0);
+    const decision = confidence > 0.8 ? 'BLOCK' : confidence > 0.5 ? 'FLAG' : 'ALLOW';
+
+    await prisma.spamAuditLog.create({
+      data: {
+        userId: 'system',
+        phoneNumber: validated,
+        decision: decision as any,
+        reason: `Rule-based analysis`,
+        ruleId: ruleMatches[0],
+      },
+    });
+
+    return { decision, confidence, ruleMatches };
+  }
+
+  async recordFeedback(
+    userId: string,
+    phoneNumber: string,
+    isSpam: boolean,
+    label?: string
+  ): Promise<void> {
+    const validated = this.validatePhoneNumber(phoneNumber);
+    const encrypted = FieldEncryptionService.encrypt(validated);
+    const hash = FieldEncryptionService.hashPhoneNumber(validated);
+
+    await prisma.spamFeedback.create({
+      data: {
+        userId,
+        phoneNumber: encrypted,
+        phoneNumberHash: hash,
+        isSpam,
+        label,
+        metadata: JSON.stringify({ source: 'user_feedback' }),
+      },
+    });
+  }
+
+  getCircuitMetrics(): CircuitMetrics {
+    return {
+      hiya: this.hiyaBreaker.getMetrics(),
+      truecaller: this.truecallerBreaker.getMetrics(),
+    };
+  }
+
+  resetCircuits(): void {
+    this.hiyaBreaker.reset();
+    this.truecallerBreaker.reset();
+  }
+
+  private async fetchHiyaReputation(phoneNumber: string): Promise<number> {
+    if (!spamFeatureFlags.enableHiyaIntegration) {
+      throw new Error('Hiya integration disabled');
+    }
+
+    return this.hiyaBreaker.execute(
+      async () => {
+        const url = `https://api.hiya.com/reputation/${encodeURIComponent(phoneNumber)}`;
+        const response = await fetch(url, {
+          method: 'GET',
+          headers: {
+            'Authorization': `Bearer ${process.env.HIYA_API_KEY}`,
+            'Accept': 'application/json',
+          },
+        });
+
+        if (!response.ok) {
+          throw new Error(`Hiya API error: ${response.status} ${response.statusText}`);
+        }
+
+        const data = await response.json() as { spamScore?: number; reputation?: { score?: number } };
+        const score = data.spamScore ?? data.reputation?.score ?? 0;
+        return score;
+      },
+      () => {
+        console.log('[SpamShield] Hiya fallback: circuit OPEN, returning neutral score');
+        return 0.5;
+      }
+    );
+  }
+
+  private async fetchTruecallerReputation(phoneNumber: string): Promise<number> {
+    if (!spamFeatureFlags.enableTruecallerIntegration) {
+      throw new Error('Truecaller integration disabled');
+    }
+
+    return this.truecallerBreaker.execute(
+      async () => {
+        const url = `https://redirect.truecaller.com/api/v2-ac/absolute/${encodeURIComponent(phoneNumber)}`;
+        const response = await fetch(url, {
+          method: 'GET',
+          headers: {
+            'contentType': 'lookupNumber',
+            'Authorization': `Basic ${Buffer.from(process.env.TRUECALLER_API_KEY || '').toString('base64')}`,
+            'Accept': 'application/json',
+          },
+        });
+
+        if (!response.ok) {
+          throw new Error(`Truecaller API error: ${response.status} ${response.statusText}`);
+        }
+
+        const data = await response.json() as { spamProbability?: number; spam_type?: number };
+        const probability = data.spamProbability ?? (data.spam_type ? 0.8 : 0);
+        return probability;
+      },
+      () => {
+        console.log('[SpamShield] Truecaller fallback: circuit OPEN, returning neutral score');
+        return 0.5;
+      }
+    );
+  }
+
+  private validatePhoneNumber(phoneNumber: string): string {
+    if (phoneNumber.length < spamConfig.minPhoneNumberLength ||
+        phoneNumber.length > spamConfig.maxPhoneNumberLength) {
+      throw new Error(`Invalid phone number format: ${phoneNumber}`);
+    }
+    return phoneNumber;
+  }
+
+  private async getActiveRules(): Promise<Array<{ id: string; pattern: string }>> {
+    return prisma.spamRule.findMany({
+      where: { isActive: true },
+      select: { id: true, pattern: true },
+    });
+  }
+}
diff --git a/services/spamshield/test/circuit-breaker.test.ts b/services/spamshield/test/circuit-breaker.test.ts
new file mode 100644
index 0000000..658e245
--- /dev/null
+++ b/services/spamshield/test/circuit-breaker.test.ts
@@ -0,0 +1,285 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { CircuitBreaker, CircuitBreakerError, CircuitState } from '../src/circuit-breaker';
+
+const fail = async () => { throw new Error('fail'); };
+const success = async () => 'ok';
+
+async function executeOrFail<T>(breaker: CircuitBreaker, fn: () => Promise<T>, fallback?: () => T): Promise<T | Error> {
+  try {
+    return await breaker.execute(fn, fallback);
+  } catch (e) {
+    return e as Error;
+  }
+}
+
+describe('CircuitBreaker', () => {
+  let stateChanges: Array<{ state: CircuitState; previous: CircuitState }>;
+
+  beforeEach(() => {
+    stateChanges = [];
+  });
+
+  describe('initial state', () => {
+    it('starts as CLOSED', () => {
+      const breaker = new CircuitBreaker();
+      expect(breaker.getState()).toBe('CLOSED');
+    });
+
+    it('uses default thresholds', () => {
+      const breaker = new CircuitBreaker();
+      const metrics = breaker.getMetrics();
+      expect(metrics.failureCount).toBe(0);
+      expect(metrics.successCount).toBe(0);
+      expect(metrics.totalExecutions).toBe(0);
+    });
+  });
+
+  describe('custom configuration', () => {
+    it('accepts custom failure threshold', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 3 });
+      for (let i = 0; i < 3; i++) {
+        await executeOrFail(breaker, fail);
+      }
+      expect(breaker.getState()).toBe('OPEN');
+    });
+
+    it('accepts custom timeout', () => {
+      const breaker = new CircuitBreaker({ timeout: 1000 });
+      expect(breaker.getState()).toBe('CLOSED');
+    });
+
+    it('calls onStateChange callback on transitions', async () => {
+      const breaker = new CircuitBreaker({
+        failureThreshold: 2,
+        onStateChange: (state, previous) => {
+          stateChanges.push({ state, previous });
+        },
+      });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+
+      expect(stateChanges).toHaveLength(1);
+      expect(stateChanges[0]).toEqual({ state: 'OPEN', previous: 'CLOSED' });
+    });
+  });
+
+  describe('state transitions', () => {
+    it('transitions to OPEN after reaching failure threshold', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 3 });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+      expect(breaker.getState()).toBe('CLOSED');
+
+      await executeOrFail(breaker, fail);
+      expect(breaker.getState()).toBe('OPEN');
+    });
+
+    it('transitions from OPEN to HALF_OPEN after timeout', async () => {
+      const breaker = new CircuitBreaker({
+        failureThreshold: 2,
+        timeout: 200,
+      });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+      expect(breaker.getState()).toBe('OPEN');
+
+      await new Promise((resolve) => setTimeout(resolve, 250));
+      expect(breaker.getState()).toBe('HALF_OPEN');
+    });
+
+    it('transitions from HALF_OPEN to CLOSED after success threshold', async () => {
+      const breaker = new CircuitBreaker({
+        failureThreshold: 2,
+        successThreshold: 3,
+        timeout: 100,
+      });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+      expect(breaker.getState()).toBe('OPEN');
+
+      await new Promise((resolve) => setTimeout(resolve, 150));
+
+      const r1 = await breaker.execute(success);
+      const r2 = await breaker.execute(success);
+      expect(r1).toBe('ok');
+      expect(r2).toBe('ok');
+      expect(breaker.getState()).toBe('HALF_OPEN');
+
+      const r3 = await breaker.execute(success);
+      expect(r3).toBe('ok');
+      expect(breaker.getState()).toBe('CLOSED');
+    });
+
+    it('transitions from HALF_OPEN back to OPEN on failure', async () => {
+      const breaker = new CircuitBreaker({
+        failureThreshold: 2,
+        timeout: 100,
+      });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+
+      await new Promise((resolve) => setTimeout(resolve, 150));
+      expect(breaker.getState()).toBe('HALF_OPEN');
+
+      await executeOrFail(breaker, fail);
+      expect(breaker.getState()).toBe('OPEN');
+    });
+  });
+
+  describe('execute with fallback', () => {
+    it('returns fallback value when circuit is OPEN', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 2 });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+
+      const result = await breaker.execute(
+        async () => { throw new Error('should not reach'); },
+        () => 'fallback-value'
+      );
+
+      expect(result).toBe('fallback-value');
+    });
+
+    it('returns fallback value when API throws in OPEN state', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 1 });
+
+      await executeOrFail(breaker, fail);
+
+      const originalFn = vi.fn(() => { throw new Error('api error'); });
+      const fallbackFn = vi.fn(() => 0.5);
+
+      const result = await breaker.execute(originalFn, fallbackFn);
+      expect(result).toBe(0.5);
+      expect(fallbackFn).toHaveBeenCalled();
+    });
+
+    it('executes function normally when circuit is CLOSED', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 3 });
+      const fn = vi.fn(async () => 'success');
+
+      const result = await breaker.execute(fn, () => 'fallback');
+      expect(result).toBe('success');
+      expect(fn).toHaveBeenCalled();
+    });
+
+    it('uses fallback when circuit is OPEN', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 1 });
+      await executeOrFail(breaker, fail);
+
+      const fn = vi.fn(async () => 'original');
+      const fallback = vi.fn(() => 'fallback-value');
+
+      const result = await breaker.execute(fn, fallback);
+      expect(result).toBe('fallback-value');
+      expect(fallback).toHaveBeenCalled();
+    });
+
+    it('throws CircuitBreakerError when OPEN and no fallback', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 1 });
+      await executeOrFail(breaker, fail);
+
+      const result = await executeOrFail(breaker, async () => 'value');
+      expect(result).toBeInstanceOf(CircuitBreakerError);
+      expect((result as CircuitBreakerError).state).toBe('OPEN');
+    });
+
+    it('throws original error when fallback also fails in CLOSED state', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 5 });
+
+      const originalError = new Error('api error');
+      const result = await executeOrFail(
+        breaker,
+        async () => { throw originalError; },
+        () => { throw new Error('fallback error'); }
+      );
+      expect(result).toBe(originalError);
+    });
+  });
+
+  describe('metrics', () => {
+    it('tracks total executions', async () => {
+      const breaker = new CircuitBreaker();
+      await breaker.execute(success);
+      await breaker.execute(success);
+
+      const metrics = breaker.getMetrics();
+      expect(metrics.totalExecutions).toBe(2);
+      expect(metrics.totalSuccesses).toBe(2);
+      expect(metrics.totalFailures).toBe(0);
+    });
+
+    it('tracks failures', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 5 });
+      await executeOrFail(breaker, fail);
+
+      const metrics = breaker.getMetrics();
+      expect(metrics.totalExecutions).toBe(1);
+      expect(metrics.totalFailures).toBe(1);
+      expect(metrics.failureCount).toBe(1);
+    });
+
+    it('includes state change timestamp', () => {
+      const breaker = new CircuitBreaker();
+      const metrics = breaker.getMetrics();
+      expect(metrics.stateChangedAt).toBeDefined();
+      expect(metrics.stateChangedAt!.getTime()).toBeGreaterThan(Date.now() - 1000);
+    });
+
+    it('tracks last failure and success times', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 5 });
+      const before = Date.now();
+
+      await breaker.execute(success);
+      await new Promise((resolve) => setTimeout(resolve, 10));
+      await executeOrFail(breaker, fail);
+
+      const metrics = breaker.getMetrics();
+      expect(metrics.lastSuccessTime!.getTime()).toBeGreaterThanOrEqual(before);
+      expect(metrics.lastFailureTime!.getTime()).toBeGreaterThanOrEqual(metrics.lastSuccessTime!.getTime());
+    });
+  });
+
+  describe('reset', () => {
+    it('resets circuit to CLOSED state', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 2 });
+
+      await executeOrFail(breaker, fail);
+      await executeOrFail(breaker, fail);
+      expect(breaker.getState()).toBe('OPEN');
+
+      breaker.reset();
+      expect(breaker.getState()).toBe('CLOSED');
+
+      const metrics = breaker.getMetrics();
+      expect(metrics.failureCount).toBe(0);
+      expect(metrics.successCount).toBe(0);
+    });
+
+    it('allows execution after reset', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 1 });
+      await executeOrFail(breaker, fail);
+
+      breaker.reset();
+      const result = await breaker.execute(success);
+      expect(result).toBe('ok');
+    });
+  });
+
+  describe('CircuitBreakerError', () => {
+    it('includes circuit state in error', async () => {
+      const breaker = new CircuitBreaker({ failureThreshold: 1 });
+      await executeOrFail(breaker, fail);
+
+      const result = await executeOrFail(breaker, success);
+      expect(result).toBeInstanceOf(CircuitBreakerError);
+      expect((result as CircuitBreakerError).state).toBe('OPEN');
+      expect((result as CircuitBreakerError).message).toContain('OPEN');
+    });
+  });
+});
diff --git a/services/spamshield/test/spamshield.test.ts b/services/spamshield/test/spamshield.test.ts
new file mode 100644
index 0000000..8b62260
--- /dev/null
+++ b/services/spamshield/test/spamshield.test.ts
@@ -0,0 +1,199 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { SpamShieldService } from '../src/services/spamshield.service';
+import { spamConfig } from '../src/config/spamshield.config';
+
+const mockFetch = vi.fn();
+global.fetch = mockFetch as unknown as typeof global.fetch;
+
+describe('SpamShieldService', () => {
+  let service: SpamShieldService;
+
+  beforeEach(() => {
+    service = SpamShieldService.getInstance();
+    service.resetCircuits();
+    mockFetch.mockReset();
+    vi.clearAllMocks();
+  });
+
+  describe('checkReputation', () => {
+    it('combines scores from both Hiya and Truecaller', async () => {
+      mockFetch
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({ spamScore: 0.8 }),
+        } as Response)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({ spamProbability: 0.9 }),
+        } as Response);
+
+      const result = await service.checkReputation('+1234567890');
+
+      expect(result.source).toBe('combined');
+      expect(result.score).toBeCloseTo(0.85, 2);
+      expect(result.isSpam).toBe(true);
+      expect(result.hiyaScore).toBe(0.8);
+      expect(result.truecallerScore).toBe(0.9);
+      expect(mockFetch).toHaveBeenCalledTimes(2);
+    });
+
+    it('uses Hiya score + Truecaller fallback when Truecaller API fails', async () => {
+      mockFetch
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({ spamScore: 0.6 }),
+        } as Response)
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 500,
+          statusText: 'Internal Server Error',
+        } as Response);
+
+      const result = await service.checkReputation('+1234567890');
+
+      expect(result.source).toBe('combined');
+      expect(result.hiyaScore).toBe(0.6);
+      expect(result.truecallerScore).toBe(0.5);
+    });
+
+    it('uses Hiya fallback + Truecaller score when Hiya API fails', async () => {
+      mockFetch
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 429,
+          statusText: 'Too Many Requests',
+        } as Response)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({ spamProbability: 0.3 }),
+        } as Response);
+
+      const result = await service.checkReputation('+1234567890');
+
+      expect(result.source).toBe('combined');
+      expect(result.hiyaScore).toBe(0.5);
+      expect(result.truecallerScore).toBe(0.3);
+    });
+
+    it('uses both fallbacks when both APIs fail', async () => {
+      mockFetch
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 503,
+          statusText: 'Service Unavailable',
+        } as Response)
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 503,
+          statusText: 'Service Unavailable',
+        } as Response);
+
+      const result = await service.checkReputation('+1234567890');
+
+      expect(result.source).toBe('combined');
+      expect(result.hiyaScore).toBe(0.5);
+      expect(result.truecallerScore).toBe(0.5);
+      expect(result.score).toBe(0.5);
+      expect(result.isSpam).toBe(false);
+    });
+
+    it('validates phone number length', async () => {
+      const shortNumber = '123';
+      const result = service.checkReputation(shortNumber);
+      await expect(result).rejects.toThrow('Invalid phone number format');
+    });
+
+    it('returns non-spam for low scores', async () => {
+      mockFetch
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({ spamScore: 0.2 }),
+        } as Response)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({ spamProbability: 0.1 }),
+        } as Response);
+
+      const result = await service.checkReputation('+1234567890');
+
+      expect(result.isSpam).toBe(false);
+      expect(result.score).toBeCloseTo(0.15, 2);
+    });
+  });
+
+  describe('circuit breaker integration', () => {
+    it('opens circuit after consecutive failures', async () => {
+      const metricsBefore = service.getCircuitMetrics();
+      expect(metricsBefore.hiya.state).toBe('CLOSED');
+
+      for (let i = 0; i < spamConfig.circuitBreakerThreshold; i++) {
+        mockFetch
+          .mockResolvedValueOnce({
+            ok: false,
+            status: 500,
+            statusText: 'Server Error',
+          } as Response)
+          .mockResolvedValueOnce({
+            ok: false,
+            status: 500,
+            statusText: 'Server Error',
+          } as Response);
+        await service.checkReputation('+1234567890');
+      }
+
+      const metricsAfter = service.getCircuitMetrics();
+      expect(metricsAfter.hiya.totalFailures).toBeGreaterThanOrEqual(spamConfig.circuitBreakerThreshold);
+      expect(metricsAfter.truecaller.totalFailures).toBeGreaterThanOrEqual(spamConfig.circuitBreakerThreshold);
+    });
+
+    it('exposes circuit metrics for monitoring', () => {
+      const metrics = service.getCircuitMetrics();
+
+      expect(metrics.hiya).toHaveProperty('state', 'CLOSED');
+      expect(metrics.hiya).toHaveProperty('failureCount');
+      expect(metrics.hiya).toHaveProperty('successCount');
+      expect(metrics.hiya).toHaveProperty('totalExecutions');
+      expect(metrics.hiya).toHaveProperty('totalFailures');
+      expect(metrics.hiya).toHaveProperty('totalSuccesses');
+      expect(metrics.hiya).toHaveProperty('lastFailureTime');
+      expect(metrics.hiya).toHaveProperty('lastSuccessTime');
+      expect(metrics.hiya).toHaveProperty('stateChangedAt');
+
+      expect(metrics.truecaller).toHaveProperty('state', 'CLOSED');
+    });
+
+    it('resets circuits to CLOSED state', () => {
+      service.resetCircuits();
+      const metrics = service.getCircuitMetrics();
+      expect(metrics.hiya.state).toBe('CLOSED');
+      expect(metrics.truecaller.state).toBe('CLOSED');
+    });
+
+    it('returns fallback scores when circuits are open', async () => {
+      service.resetCircuits();
+
+      for (let i = 0; i < spamConfig.circuitBreakerThreshold; i++) {
+        mockFetch
+          .mockResolvedValueOnce({
+            ok: false,
+            status: 500,
+            statusText: 'Server Error',
+          } as Response)
+          .mockResolvedValueOnce({
+            ok: false,
+            status: 500,
+            statusText: 'Server Error',
+          } as Response);
+        await service.checkReputation('+1234567890');
+      }
+
+      const metrics = service.getCircuitMetrics();
+      expect(metrics.hiya.state).toBe('OPEN');
+      expect(metrics.truecaller.state).toBe('OPEN');
+
+      const result = await service.checkReputation('+1234567890');
+      expect(result.hiyaScore).toBe(0.5);
+      expect(result.truecallerScore).toBe(0.5);
+    });
+  });
+});