diff --git a/services/spamshield/src/constants/decision-engine.constants.ts b/services/spamshield/src/constants/decision-engine.constants.ts
new file mode 100644
index 0000000..f64c4b7
--- /dev/null
+++ b/services/spamshield/src/constants/decision-engine.constants.ts
@@ -0,0 +1,27 @@
+/**
+ * Decision Engine Constants
+ * 
+ * Scoring weights, thresholds, and behavioral factors used in spam detection.
+ * These values should be reviewed periodically and updated based on model performance.
+ */
+
+/** Scoring Weights */
+export const DEFAULT_REPUTATION_WEIGHT = 0.4;
+export const DEFAULT_RULE_WEIGHT = 0.3;
+export const DEFAULT_BEHAVIORAL_WEIGHT = 0.2;
+export const DEFAULT_USER_HISTORY_WEIGHT = 0.1;
+
+/** Decision Thresholds */
+export const DEFAULT_BLOCK_THRESHOLD = 0.85;
+export const DEFAULT_FLAG_THRESHOLD = 0.60;
+
+/** Behavioral Analysis Scores */
+export const SHORT_CALL_SCORE = 0.3;      // Call duration < 5 seconds
+export const SHORT_SMS_SCORE = 0.1;       // SMS call type
+export const SHORT_CONTENT_SCORE = 0.2;   // SMS body < 10 characters
+export const URGENT_KEYWORD_SCORE = 0.3;  // Contains urgent/act now/limited keywords
+
+/** Default Fallback Values */
+export const DEFAULT_EVALUATION_TIMEOUT = 200; // milliseconds
+export const DEFAULT_FALLBACK_DECISION = 'ALLOW';
+export const DEFAULT_FALLBACK_ON_TIMEOUT = true;
diff --git a/services/spamshield/src/engine/decision-engine.ts b/services/spamshield/src/engine/decision-engine.ts
index e2c1d2a..d7ffccc 100644
--- a/services/spamshield/src/engine/decision-engine.ts
+++ b/services/spamshield/src/engine/decision-engine.ts
@@ -1,5 +1,16 @@
 import { SpamShieldService, ReputationResult } from '../services/spamshield.service';
 import { RuleEngine, RuleMatch } from './rule-engine';
+import {
+  DEFAULT_REPUTATION_WEIGHT,
+  DEFAULT_RULE_WEIGHT,
+  DEFAULT_BEHAVIORAL_WEIGHT,
+  DEFAULT_USER_HISTORY_WEIGHT,
+  DEFAULT_BLOCK_THRESHOLD,
+  DEFAULT_FLAG_THRESHOLD,
+  DEFAULT_EVALUATION_TIMEOUT,
+  DEFAULT_FALLBACK_DECISION,
+  DEFAULT_FALLBACK_ON_TIMEOUT,
+} from '../constants/decision-engine.constants';
 
 export interface CallMetadata {
   callId: string;
@@ -69,17 +80,7 @@ export interface DecisionEngineConfig {
   fallbackDecision?: 'BLOCK' | 'FLAG' | 'ALLOW';
 }
 
-const DEFAULT_CONFIG: Required<DecisionEngineConfig> = {
-  reputationWeight: 0.4,
-  ruleWeight: 0.3,
-  behavioralWeight: 0.2,
-  userHistoryWeight: 0.1,
-  blockThreshold: 0.85,
-  flagThreshold: 0.60,
-  evaluationTimeout: 200,
-  fallbackOnTimeout: true,
-  fallbackDecision: 'ALLOW',
-};
+// Configuration defaults exported from constants module
 
 export class DecisionEngine {
   private readonly config: Required<DecisionEngineConfig>;
@@ -91,7 +92,17 @@ export class DecisionEngine {
     ruleEngine: RuleEngine,
     config?: DecisionEngineConfig
   ) {
-    this.config = { ...DEFAULT_CONFIG, ...config };
+    this.config = {
+      reputationWeight: config?.reputationWeight ?? DEFAULT_REPUTATION_WEIGHT,
+      ruleWeight: config?.ruleWeight ?? DEFAULT_RULE_WEIGHT,
+      behavioralWeight: config?.behavioralWeight ?? DEFAULT_BEHAVIORAL_WEIGHT,
+      userHistoryWeight: config?.userHistoryWeight ?? DEFAULT_USER_HISTORY_WEIGHT,
+      blockThreshold: config?.blockThreshold ?? DEFAULT_BLOCK_THRESHOLD,
+      flagThreshold: config?.flagThreshold ?? DEFAULT_FLAG_THRESHOLD,
+      evaluationTimeout: config?.evaluationTimeout ?? DEFAULT_EVALUATION_TIMEOUT,
+      fallbackOnTimeout: config?.fallbackOnTimeout ?? DEFAULT_FALLBACK_ON_TIMEOUT,
+      fallbackDecision: config?.fallbackDecision ?? DEFAULT_FALLBACK_DECISION,
+    };
     this.reputationService = reputationService;
     this.ruleEngine = ruleEngine;
   }