diff --git a/packages/noir-ethereum-api/src/arrays.ts b/packages/noir-ethereum-api/src/arrays.ts
index 39cae0854..4aab750b0 100644
--- a/packages/noir-ethereum-api/src/arrays.ts
+++ b/packages/noir-ethereum-api/src/arrays.ts
@@ -1,4 +1,5 @@
 import { assert } from './assert.js';
+import { incHexByte } from './utils/string.js';
 
 type PaddingDirection = 'left' | 'right';
 
@@ -18,8 +19,3 @@ export const alterArray = function (array: readonly string[]): string[] {
   assert(array.length > 0, 'Array should not be empty');
   return [incHexByte(array[0]), ...array.slice(1)];
 };
-
-function incHexByte(hexByte: string): string {
-  const newByte = ((parseInt(hexByte) + 1) % 256).toString(16);
-  return '0x' + newByte;
-}
diff --git a/packages/noir-ethereum-api/src/ethereum/mockClient.ts b/packages/noir-ethereum-api/src/ethereum/mockClient.ts
index 4338f4cb2..c7d4ce85d 100644
--- a/packages/noir-ethereum-api/src/ethereum/mockClient.ts
+++ b/packages/noir-ethereum-api/src/ethereum/mockClient.ts
@@ -4,13 +4,17 @@ import { assert } from '../assert.js';
 import { readObject } from '../utils/file.js';
 import { mock } from '../utils/mock.js';
 import isEqual from 'lodash.isequal';
+import { identity } from '../utils/function.js';
 
-export async function createMockClient(filePath: string): Promise<PublicClient> {
+export async function createMockClient(
+  filePath: string,
+  resultModifier: (call: Call) => Call = identity
+): Promise<PublicClient> {
   const savedCalls = await readObject<Call[]>(filePath);
 
   return mock<PublicClient>(isEthereumApiMethod, (method: string, args: object): object => {
     const call: Call | undefined = savedCalls.find((it) => it.method === method && isEqual(it.arguments, args));
     assert(!!call, `call not found for: ${method}(${args})`);
-    return call.result;
+    return resultModifier(call).result;
   });
 }
diff --git a/packages/noir-ethereum-api/src/noir/oracles/oracles.ts b/packages/noir-ethereum-api/src/noir/oracles/oracles.ts
index 13d9c00bd..5c641b1fc 100644
--- a/packages/noir-ethereum-api/src/noir/oracles/oracles.ts
+++ b/packages/noir-ethereum-api/src/noir/oracles/oracles.ts
@@ -2,6 +2,7 @@ import { type ForeignCallOutput } from '@noir-lang/noir_js';
 import { createDefaultClient } from '../../ethereum/client.js';
 import { getAccountOracle } from './accountOracles.js';
 import { type PublicClient } from 'viem';
+import { getHeaderOracle } from './headerOracle.js';
 
 export type NoirArguments = string[][];
 
@@ -22,4 +23,9 @@ export const createOracles =
     return await fn(client, args);
   };
 
-export const defaultOracles = createOracles(createDefaultClient())({ getAccountOracle });
+export const defaultOraclesMap = {
+  get_account: getAccountOracle,
+  get_header: getHeaderOracle
+};
+
+export const defaultOracles = createOracles(createDefaultClient())(defaultOraclesMap);
diff --git a/packages/noir-ethereum-api/src/utils/function.ts b/packages/noir-ethereum-api/src/utils/function.ts
new file mode 100644
index 000000000..8aa070f5f
--- /dev/null
+++ b/packages/noir-ethereum-api/src/utils/function.ts
@@ -0,0 +1 @@
+export const identity = <T>(it: T): T => it;
diff --git a/packages/noir-ethereum-api/src/utils/object.ts b/packages/noir-ethereum-api/src/utils/object.ts
new file mode 100644
index 000000000..01cea569a
--- /dev/null
+++ b/packages/noir-ethereum-api/src/utils/object.ts
@@ -0,0 +1,8 @@
+export function updateNestedField<T, V>(obj: T, pathArray: string[], updater: (value: V) => V): void {
+  /* eslint-disable-next-line @typescript-eslint/no-explicit-any */
+  pathArray.reduce((acc: any, key: string, i: number) => {
+    if (acc[key] === undefined) acc[key] = {};
+    if (i === pathArray.length - 1) acc[key] = updater(acc[key]);
+    return acc[key];
+  }, obj);
+}
diff --git a/packages/noir-ethereum-api/src/utils/string.ts b/packages/noir-ethereum-api/src/utils/string.ts
new file mode 100644
index 000000000..66867e1cc
--- /dev/null
+++ b/packages/noir-ethereum-api/src/utils/string.ts
@@ -0,0 +1,8 @@
+export function incHexStr(hexStr: string): string {
+  return '0x' + (BigInt(hexStr) + 1n).toString(16);
+}
+
+export function incHexByte(hexByte: string): string {
+  const newByte = ((parseInt(hexByte) + 1) % 256).toString(16);
+  return '0x' + newByte;
+}
diff --git a/packages/noir-ethereum-api/test/e2e.test.ts b/packages/noir-ethereum-api/test/e2e.test.ts
index 66b695e6d..521620315 100644
--- a/packages/noir-ethereum-api/test/e2e.test.ts
+++ b/packages/noir-ethereum-api/test/e2e.test.ts
@@ -1,15 +1,15 @@
-import { describe, expect, it } from 'vitest';
-import { generateAndVerifyStorageProof, type MainInputs } from '../src/main.js';
-import { encodeAddress } from '../src/noir/encode.js';
-import { createOracles, type Oracles } from '../src/noir/oracles/oracles.js';
-import accountWithProofJSON from './fixtures/accountWithProof.json';
-import { AccountWithProof, expectCircuitFail, type FieldsOfType, serializeAccountWithProof } from './helpers.js';
-import { blockHeaders } from './fixtures/blockHeader.json';
-import { encodeBlockHeaderPartial } from '../src/noir/oracles/headerOracle.js';
-import { type BlockHeader } from '../src/ethereum/blockHeader.js';
+import { PublicClient } from 'viem';
+import { beforeAll, describe, expect, it } from 'vitest';
 import { alterArray } from '../src/arrays.js';
+import { incHexStr } from '../src/utils/string.js';
 import { createMockClient } from '../src/ethereum/mockClient.js';
+import { Call } from '../src/ethereum/recordingClient.js';
+import { generateAndVerifyStorageProof, type MainInputs } from '../src/main.js';
+import { encodeAddress } from '../src/noir/encode.js';
+import { createOracles, defaultOraclesMap, type Oracles } from '../src/noir/oracles/oracles.js';
 import { ADDRESS } from './ethereum/recordingClient.test.js';
+import { expectCircuitFail } from './helpers.js';
+import { updateNestedField } from '../src/utils/object.js';
 
 const defaultTestCircuitInputParams: MainInputs = {
   block_no: 14194126,
@@ -20,33 +20,35 @@ const defaultTestCircuitInputParams: MainInputs = {
     '0xda', '0xc4', '0x8e', '0x2b', '0x4']
 };
 
+function alterCall(callName: string, path: string[]) {
+  return (call: Call): Call => {
+    if (call.method === callName) {
+      updateNestedField(call, path, incHexStr);
+    }
+    return call;
+  };
+}
 describe(
   'e2e',
-  async () => {
-    async function oracles(accountWithProof: AccountWithProof = accountWithProofJSON): Promise<Oracles> {
-      return createOracles(await createMockClient('./test/fixtures/mockClientData.json'))({
-        get_account: async () => serializeAccountWithProof(accountWithProof),
-        get_header: async () => encodeBlockHeaderPartial(blockHeaders[1].header as BlockHeader)
-      });
-    }
+  () => {
+    let client: PublicClient;
+    let oracles: Oracles;
+
+    beforeAll(async () => {
+      client = await createMockClient('./test/fixtures/mockClientData.json');
+      oracles = createOracles(client)(defaultOraclesMap);
+    });
 
     it('proof successes', async () => {
-      expect(await generateAndVerifyStorageProof(defaultTestCircuitInputParams, await oracles())).toEqual(true);
+      expect(await generateAndVerifyStorageProof(defaultTestCircuitInputParams, oracles)).toEqual(true);
     });
 
-    const arrayKeys: Array<FieldsOfType<AccountWithProof, readonly string[]>> = ['key', 'value', 'proof'];
-    arrayKeys.forEach((arrayField) => {
-      it(`proof fails: invalid field: ${arrayField}`, async () => {
-        await expectCircuitFail(
-          generateAndVerifyStorageProof(
-            defaultTestCircuitInputParams,
-            await oracles({
-              ...accountWithProofJSON,
-              [arrayField]: alterArray(accountWithProofJSON[arrayField])
-            })
-          )
-        );
-      });
+    it('proof fails: invalid proof', async () => {
+      const resultModifier = alterCall('getProof', ['result', 'accountProof', '0']);
+      const oracles = createOracles(await createMockClient('./test/fixtures/mockClientData.json', resultModifier))(
+        defaultOraclesMap
+      );
+      await expectCircuitFail(generateAndVerifyStorageProof(defaultTestCircuitInputParams, oracles));
     });
 
     it('proof fails: invalid state root', async () => {
@@ -54,7 +56,7 @@ describe(
         ...defaultTestCircuitInputParams,
         state_root: alterArray(defaultTestCircuitInputParams.state_root)
       };
-      await expectCircuitFail(generateAndVerifyStorageProof(inputParams, await oracles()));
+      await expectCircuitFail(generateAndVerifyStorageProof(inputParams, oracles));
     });
   },
   {
diff --git a/packages/noir-ethereum-api/test/utils/object.test.ts b/packages/noir-ethereum-api/test/utils/object.test.ts
new file mode 100644
index 000000000..3b1c2443a
--- /dev/null
+++ b/packages/noir-ethereum-api/test/utils/object.test.ts
@@ -0,0 +1,17 @@
+import { updateNestedField } from '../../src/utils/object.js';
+import { describe, it, expect } from 'vitest';
+
+describe('updateNestedField', () => {
+  it('existing key', () => {
+    const object = { a: [{ bar: { c: 3 } }] };
+    updateNestedField(object, ['a', '0', 'bar', 'c'], (x: number) => x + 1);
+    expect(object.a[0].bar.c).to.eq(4);
+  });
+
+  it('non-existing key', () => {
+    const object = { a: [{ bar: { c: 3 } }] };
+    updateNestedField(object, ['x', '0', 'y', 'z'], () => 5);
+    /* eslint-disable-next-line @typescript-eslint/no-explicit-any */
+    expect((object as any).x[0]?.y?.z).to.eq(5);
+  });
+});
diff --git a/packages/noir-ethereum-api/test/utils/string.test.ts b/packages/noir-ethereum-api/test/utils/string.test.ts
new file mode 100644
index 000000000..51049cee7
--- /dev/null
+++ b/packages/noir-ethereum-api/test/utils/string.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest';
+import { incHexByte, incHexStr } from '../../src/utils/string.js';
+
+describe('incHexStr', () => {
+  it('zero', () => {
+    expect(incHexStr('0x0')).toEqual('0x1');
+  });
+
+  it('small', () => {
+    expect(incHexStr('0x10')).toEqual('0x11');
+  });
+
+  it('big', () => {
+    expect(incHexStr('0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff1')).toEqual(
+      '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff2'
+    );
+  });
+});
+
+describe('incHexByte', () => {
+  it('zero', () => {
+    expect(incHexByte('0x0')).toEqual('0x1');
+  });
+
+  it('mid size', () => {
+    expect(incHexByte('0xaa')).toEqual('0xab');
+    expect(incHexByte('0xAA')).toEqual('0xab');
+  });
+
+  it('oveflow', () => {
+    expect(incHexByte('0xFF')).toEqual('0x0');
+  });
+});