diff --git a/packages/verifier-runtime/src/cache.test.ts b/packages/verifier-runtime/src/cache.test.ts
new file mode 100644
index 0000000..9de6de5
--- /dev/null
+++ b/packages/verifier-runtime/src/cache.test.ts
@@ -0,0 +1,111 @@
+import { expect, test } from 'bun:test';
+import { VerifyResultCache, verifierCache } from './cache.js';
+import type { VerifyInput } from './verify.js';
+
+test('VerifyResultCache constructor creates an empty cache', () => {
+  const cache = new VerifyResultCache();
+  expect(cache.size).toBe(0);
+});
+
+test('VerifyResultCache.set and .get round-trip', () => {
+  const cache = new VerifyResultCache();
+  const result = { passed: true, expected_hash: 'abc', actual_hash: 'abc' };
+  const input: VerifyInput = {
+    taskId: 'test-normalize-1',
+    input: { a: 1 },
+    output: { a: 1 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  };
+  const key = VerifyResultCache.key(input);
+  cache.set(key, result);
+  expect(cache.get(key)).toEqual(result);
+  expect(cache.size).toBe(1);
+});
+
+test('VerifyResultCache returns undefined for cache miss', () => {
+  const cache = new VerifyResultCache();
+  expect(cache.get('nonexistent')).toBeUndefined();
+});
+
+test('VerifyResultCache.key is deterministic for same input', () => {
+  const input1: VerifyInput = {
+    taskId: 'test-normalize-1',
+    input: { a: 1, b: 2 },
+    output: { a: 1, b: 2 },
+    constraints: { sort_keys: true, strip_nulls: false, flatten: null },
+  };
+  const input2: VerifyInput = {
+    taskId: 'test-normalize-1',
+    input: { a: 1, b: 2 },
+    output: { a: 1, b: 2 },
+    constraints: { sort_keys: true, strip_nulls: false, flatten: null },
+  };
+  expect(VerifyResultCache.key(input1)).toBe(VerifyResultCache.key(input2));
+});
+
+test('VerifyResultCache.key differs for different outputs', () => {
+  const input1: VerifyInput = {
+    taskId: 'test-normalize-1',
+    input: { a: 1 },
+    output: { a: 1 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  };
+  const input2: VerifyInput = {
+    taskId: 'test-normalize-1',
+    input: { a: 1 },
+    output: { a: 2 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  };
+  expect(VerifyResultCache.key(input1)).not.toBe(VerifyResultCache.key(input2));
+});
+
+test('VerifyResultCache evicts oldest entry when over max size', () => {
+  const cache = new VerifyResultCache(3);
+  const results = [
+    { passed: true, expected_hash: '1', actual_hash: '1' },
+    { passed: true, expected_hash: '2', actual_hash: '2' },
+    { passed: true, expected_hash: '3', actual_hash: '3' },
+    { passed: true, expected_hash: '4', actual_hash: '4' },
+  ];
+  for (let i = 0; i < results.length; i++) {
+    const input: VerifyInput = {
+      taskId: `test-${i}`,
+      input: { n: i },
+      output: { n: i },
+      constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+    };
+    cache.set(VerifyResultCache.key(input), results[i]);
+  }
+  // Fourth insert should evict the first entry.
+  const firstInput: VerifyInput = {
+    taskId: 'test-0',
+    input: { n: 0 },
+    output: { n: 0 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  };
+  expect(cache.get(VerifyResultCache.key(firstInput))).toBeUndefined();
+  expect(cache.size).toBe(3);
+});
+
+test('VerifyResultCache.clear empties the cache', () => {
+  const cache = new VerifyResultCache();
+  const input: VerifyInput = {
+    taskId: 'test-clear',
+    input: { x: 1 },
+    output: { x: 1 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  };
+  cache.set(VerifyResultCache.key(input), {
+    passed: true,
+    expected_hash: 'h',
+    actual_hash: 'h',
+  });
+  expect(cache.size).toBe(1);
+  cache.clear();
+  expect(cache.size).toBe(0);
+});
+
+test('global verifierCache singleton exists', () => {
+  expect(verifierCache).toBeDefined();
+  expect(verifierCache).toBeInstanceOf(VerifyResultCache);
+});
diff --git a/packages/verifier-runtime/src/cache.ts b/packages/verifier-runtime/src/cache.ts
new file mode 100644
index 0000000..66d5147
--- /dev/null
+++ b/packages/verifier-runtime/src/cache.ts
@@ -0,0 +1,82 @@
+/**
+ * In-memory LRU cache for verifier results keyed by content hash.
+ *
+ * This cache stores (task_spec + solver_answer) → VerifyResult mappings
+ * so that repeated identical verification calls are short-circuited.
+ * The cache is a singleton shared across the entire process.
+ *
+ * @packageDocumentation
+ */
+
+import type { VerifyInput, VerifyResult } from './verify.js';
+import { sha256Hex, stableStringify } from './crypto.js';
+
+/** Default maximum number of entries in the LRU cache. */
+const DEFAULT_MAX_SIZE = 1000;
+
+/**
+ * A minimal LRU cache implemented with a Map (iteration order = insertion order
+ * in modern JS engines). When the cache exceeds `maxSize`, the oldest entry
+ * (first inserted) is evicted.
+ */
+export class VerifyResultCache {
+  private readonly _map = new Map<string, VerifyResult>();
+  private readonly _maxSize: number;
+
+  constructor(maxSize = DEFAULT_MAX_SIZE) {
+    this._maxSize = maxSize;
+  }
+
+  /** Compute a deterministic cache key from the verify input. */
+  static key(input: VerifyInput): string {
+    // The key incorporates the task ID, operation type, input, output, and constraints
+    // so that different solver answers produce different cache entries.
+    return sha256Hex(
+      stableStringify({
+        taskId: input.taskId,
+        operationType: input.operationType,
+        input: input.input,
+        output: input.output,
+        constraints: input.constraints,
+      }),
+    );
+  }
+
+  /** Look up a cached result. Returns `undefined` on a cache miss. */
+  get(key: string): VerifyResult | undefined {
+    const value = this._map.get(key);
+    if (value !== undefined) {
+      // Refresh — delete and re-insert to maintain LRU order.
+      this._map.delete(key);
+      this._map.set(key, value);
+    }
+    return value;
+  }
+
+  /** Store a result in the cache, evicting the oldest entry if necessary. */
+  set(key: string, value: VerifyResult): void {
+    if (this._map.has(key)) {
+      this._map.delete(key);
+    } else if (this._map.size >= this._maxSize) {
+      // Evict the first (oldest) entry.
+      const oldest = this._map.keys().next();
+      if (!oldest.done) {
+        this._map.delete(oldest.value);
+      }
+    }
+    this._map.set(key, value);
+  }
+
+  /** Number of entries currently cached. */
+  get size(): number {
+    return this._map.size;
+  }
+
+  /** Clear all cached entries. */
+  clear(): void {
+    this._map.clear();
+  }
+}
+
+/** The singleton cache instance used by the verifier runtime. */
+export const verifierCache = new VerifyResultCache();
diff --git a/packages/verifier-runtime/src/index.ts b/packages/verifier-runtime/src/index.ts
index 1b6c74a..99db05b 100644
--- a/packages/verifier-runtime/src/index.ts
+++ b/packages/verifier-runtime/src/index.ts
@@ -13,6 +13,7 @@ export {
   type VerifyResult,
 } from './verify.js';
 export { sha256Hex, sha256OfString, shortHash, stableStringify } from './crypto.js';
+export { VerifyResultCache, verifierCache } from './cache.js';
 
 export interface VerifierPackage {
   id: string;
diff --git a/packages/verifier-runtime/src/verify.test.ts b/packages/verifier-runtime/src/verify.test.ts
new file mode 100644
index 0000000..b810b84
--- /dev/null
+++ b/packages/verifier-runtime/src/verify.test.ts
@@ -0,0 +1,77 @@
+import { expect, test } from 'bun:test';
+import { verify, expectedHashFor } from './verify.js';
+import { VerifyResultCache } from './cache.js';
+
+test('verify returns passed=true for correct normalize output', () => {
+  const result = verify({
+    taskId: 'test-normalize-1',
+    input: { b: 1, a: 2 },
+    output: { a: 2, b: 1 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  });
+  expect(result.passed).toBe(true);
+});
+
+test('verify returns passed=false for incorrect output', () => {
+  const result = verify({
+    taskId: 'test-normalize-1',
+    input: { a: 1 },
+    output: { a: 2 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  });
+  expect(result.passed).toBe(false);
+  expect(result.failure_reason).toBeDefined();
+});
+
+test('verify uses cache when provided', () => {
+  const cache = new VerifyResultCache(10);
+  const input = {
+    taskId: 'test-normalize-cache',
+    input: { x: 10 },
+    output: { x: 10 },
+    constraints: { sort_keys: false, strip_nulls: false, flatten: null },
+  };
+
+  // First call computes and caches.
+  const first = verify(input, cache);
+  expect(first.passed).toBe(true);
+  expect(cache.size).toBe(1);
+
+  // Second call should return cached result.
+  const second = verify(input, cache);
+  expect(second).toEqual(first);
+  // Size should not increase.
+  expect(cache.size).toBe(1);
+});
+
+test('verify caching works with the global singleton', () => {
+  // Use the global cache by omitting the cache argument.
+  const input = {
+    taskId: 'test-global-cache',
+    input: { z: 99 },
+    output: { z: 99 },
+    constraints: { sort_keys: true, strip_nulls: false, flatten: null },
+  };
+
+  const result = verify(input);
+  expect(result.passed).toBe(true);
+  // The global cache now has this result.
+});
+
+test('expectedHashFor returns a deterministic string', () => {
+  const hash1 = expectedHashFor({ a: 1 }, { sort_keys: false, strip_nulls: false, flatten: null });
+  const hash2 = expectedHashFor({ a: 1 }, { sort_keys: false, strip_nulls: false, flatten: null });
+  expect(hash1).toBe(hash2);
+  expect(typeof hash1).toBe('string');
+  expect(hash1.length).toBe(64); // SHA-256 hex
+});
+
+test('expectedHashFor with taskId infers operation', () => {
+  const hash = expectedHashFor(
+    { source: { a: 1 }, target: { a: 2 } },
+    { max_depth: 10, array_indices: true, format: 'ops' },
+    'test-diff-operation',
+  );
+  expect(typeof hash).toBe('string');
+  expect(hash.length).toBe(64);
+});
diff --git a/packages/verifier-runtime/src/verify.ts b/packages/verifier-runtime/src/verify.ts
index 5faf336..8befe8f 100644
--- a/packages/verifier-runtime/src/verify.ts
+++ b/packages/verifier-runtime/src/verify.ts
@@ -4,6 +4,7 @@ import {
   parseNormalizeConstraints,
   parseSchemaMigrationConstraints,
 } from '@fresharena/faep-schema';
+import { verifierCache, VerifyResultCache } from './cache.js';
 import { sha256Hex } from './crypto.js';
 import { apply, diff } from './diff_patch.js';
 import { merge } from './merge.js';
@@ -33,8 +34,18 @@ export interface VerifyResult {
  * For normalize, diff, patch, merge, and migrate operations, a submission passes
  * iff its structural hash equals the reference implementation's structural hash.
  * Object key order is irrelevant (see `stableStringify`); array order is significant.
+ *
+ * Results are cached by content hash so that repeated identical verification
+ * calls short-circuit the computation.
  */
-export function verify(input: VerifyInput): VerifyResult {
+export function verify(input: VerifyInput, cache?: VerifyResultCache): VerifyResult {
+  const cacheInstance = cache ?? verifierCache;
+  const cacheKey = VerifyResultCache.key(input);
+  const cached = cacheInstance.get(cacheKey);
+  if (cached !== undefined) {
+    return cached;
+  }
+
   const operationType = input.operationType || inferOperationType(input.taskId);
 
   let expected: unknown;
@@ -79,7 +90,10 @@ export function verify(input: VerifyInput): VerifyResult {
     actual_hash: actualHash,
   };
 
-  return passed ? base : { ...base, failure_reason: failureReason };
+  const result: VerifyResult = passed ? base : { ...base, failure_reason: failureReason };
+
+  cacheInstance.set(cacheKey, result);
+  return result;
 }
 
 /**