diff --git a/yarn-project/simulator/src/common/debug_fn_name.ts b/yarn-project/simulator/src/common/debug_fn_name.ts
index 8bc24788f97d..901440b3e2e0 100644
--- a/yarn-project/simulator/src/common/debug_fn_name.ts
+++ b/yarn-project/simulator/src/common/debug_fn_name.ts
@@ -2,7 +2,7 @@ import type { Fr } from '@aztec/foundation/fields';
 import { FunctionSelector } from '@aztec/stdlib/abi';
 import type { AztecAddress } from '@aztec/stdlib/aztec-address';
 
-import type { PublicContractsDBInterface } from './db_interfaces.js';
+import type { PublicContractsDBInterface } from '../public/db_interfaces.js';
 
 export async function getPublicFunctionDebugName(
   db: PublicContractsDBInterface,
diff --git a/yarn-project/simulator/src/common/index.ts b/yarn-project/simulator/src/common/index.ts
index 90dc13c923e0..32cf7b9de20b 100644
--- a/yarn-project/simulator/src/common/index.ts
+++ b/yarn-project/simulator/src/common/index.ts
@@ -1,3 +1,2 @@
 export * from './errors.js';
 export * from './stats/index.js';
-export * from './message_load_oracle_inputs.js';
diff --git a/yarn-project/simulator/src/private/acvm/oracle/typed_oracle.ts b/yarn-project/simulator/src/private/acvm/oracle/typed_oracle.ts
index 5329ed8910da..aa551d8a0f25 100644
--- a/yarn-project/simulator/src/private/acvm/oracle/typed_oracle.ts
+++ b/yarn-project/simulator/src/private/acvm/oracle/typed_oracle.ts
@@ -9,7 +9,7 @@ import type { Note, NoteStatus } from '@aztec/stdlib/note';
 import { type MerkleTreeId, type NullifierMembershipWitness, PublicDataWitness } from '@aztec/stdlib/trees';
 import type { BlockHeader, TxHash } from '@aztec/stdlib/tx';
 
-import type { MessageLoadOracleInputs } from '../../../common/message_load_oracle_inputs.js';
+import type { MessageLoadOracleInputs } from '../../message_load_oracle_inputs.js';
 
 /**
  * Information about a note needed during execution.
diff --git a/yarn-project/simulator/src/private/execution_data_provider.ts b/yarn-project/simulator/src/private/execution_data_provider.ts
index 4c2eaab4a907..791329c90f1b 100644
--- a/yarn-project/simulator/src/private/execution_data_provider.ts
+++ b/yarn-project/simulator/src/private/execution_data_provider.ts
@@ -1,3 +1,4 @@
+import type { L1_TO_L2_MSG_TREE_HEIGHT } from '@aztec/constants';
 import type { Fr, Point } from '@aztec/foundation/fields';
 import type {
   EventSelector,
@@ -14,8 +15,8 @@ import type { NoteStatus } from '@aztec/stdlib/note';
 import { type MerkleTreeId, type NullifierMembershipWitness, PublicDataWitness } from '@aztec/stdlib/trees';
 import type { BlockHeader, TxHash } from '@aztec/stdlib/tx';
 
-import type { CommitmentsDBInterface } from '../common/db_interfaces.js';
 import type { NoteData } from './acvm/index.js';
+import type { MessageLoadOracleInputs } from './message_load_oracle_inputs.js';
 
 /**
  * Error thrown when a contract is not found in the database.
@@ -38,7 +39,7 @@ export class ContractClassNotFoundError extends Error {
 /**
  * The interface for the data layer required to perform private and utility execution.
  */
-export interface ExecutionDataProvider extends CommitmentsDBInterface {
+export interface ExecutionDataProvider {
   /**
    * Returns a contract instance associated with an address, if available.
    * @param address - Address.
@@ -117,6 +118,40 @@ export interface ExecutionDataProvider extends CommitmentsDBInterface {
    */
   getNullifierIndex(nullifier: Fr): Promise<bigint | undefined>;
 
+  /**
+   * Gets the index of a nullifier in the nullifier tree.
+   * @param nullifier - The nullifier.
+   * @returns - The index of the nullifier. Undefined if it does not exist in the tree.
+   */
+  getNullifierIndex(nullifier: Fr): Promise<bigint | undefined>;
+
+  /**
+   * Returns a nullifier membership witness for the given nullifier or undefined if not found.
+   * REFACTOR: Same as getL1ToL2MembershipWitness, can be combined with aztec-node method that does almost the same thing.
+   * @param nullifier - Nullifier we're looking for.
+   */
+  getNullifierMembershipWitnessAtLatestBlock(nullifier: Fr): Promise<NullifierMembershipWitness | undefined>;
+
+  /**
+   * Fetches a message from the db, given its key.
+   * @param contractAddress - Address of a contract by which the message was emitted.
+   * @param messageHash - Hash of the message.
+   * @param secret - Secret used to compute a nullifier.
+   * @dev Contract address and secret are only used to compute the nullifier to get non-nullified messages
+   * @returns The l1 to l2 membership witness (index of message in the tree and sibling path).
+   */
+  getL1ToL2MembershipWitness(
+    contractAddress: AztecAddress,
+    messageHash: Fr,
+    secret: Fr,
+  ): Promise<MessageLoadOracleInputs<typeof L1_TO_L2_MSG_TREE_HEIGHT>>;
+
+  /**
+   * @param leafIndex the leaf to look up
+   * @returns The l1 to l2 leaf message hash or undefined if not found.
+   */
+  getL1ToL2MessageHash(leafIndex: bigint): Promise<Fr | undefined>;
+
   /**
    * Retrieve the databases view of the Block Header object.
    * This structure is fed into the circuits simulator and is used to prove against certain historical roots.
@@ -263,6 +298,13 @@ export interface ExecutionDataProvider extends CommitmentsDBInterface {
     recipient: AztecAddress,
   ): Promise<void>;
 
+  /**
+   * Gets note hash in the note hash tree at the given leaf index.
+   * @param leafIndex - the leaf to look up.
+   * @returns - The note hash at that index. Undefined if leaf index is not found.
+   */
+  getNoteHash(leafIndex: bigint): Promise<Fr | undefined>;
+
   /**
    * Searches for a log with the corresponding `tag` and returns it along with contextual transaction information.
    * Returns null if no such log exists, and throws if more than one exists.
diff --git a/yarn-project/simulator/src/private/index.ts b/yarn-project/simulator/src/private/index.ts
index 09bcc63b7393..ca990ca82283 100644
--- a/yarn-project/simulator/src/private/index.ts
+++ b/yarn-project/simulator/src/private/index.ts
@@ -13,3 +13,4 @@ export { extractCallStack } from './acvm/acvm.js';
 export { type NoteData, TypedOracle } from './acvm/oracle/typed_oracle.js';
 export { Oracle } from './acvm/oracle/oracle.js';
 export { HashedValuesCache } from './hashed_values_cache.js';
+export { MessageLoadOracleInputs } from './message_load_oracle_inputs.js';
diff --git a/yarn-project/simulator/src/common/message_load_oracle_inputs.ts b/yarn-project/simulator/src/private/message_load_oracle_inputs.ts
similarity index 100%
rename from yarn-project/simulator/src/common/message_load_oracle_inputs.ts
rename to yarn-project/simulator/src/private/message_load_oracle_inputs.ts
diff --git a/yarn-project/simulator/src/private/private_execution.test.ts b/yarn-project/simulator/src/private/private_execution.test.ts
index 25d4e5658c6f..f38987782dcd 100644
--- a/yarn-project/simulator/src/private/private_execution.test.ts
+++ b/yarn-project/simulator/src/private/private_execution.test.ts
@@ -64,9 +64,9 @@ import { jest } from '@jest/globals';
 import { Matcher, type MatcherCreator, type MockProxy, mock } from 'jest-mock-extended';
 import { toFunctionSelector } from 'viem';
 
-import { MessageLoadOracleInputs } from '../common/message_load_oracle_inputs.js';
 import { buildL1ToL2Message } from '../test/utils.js';
 import type { ExecutionDataProvider } from './execution_data_provider.js';
+import { MessageLoadOracleInputs } from './message_load_oracle_inputs.js';
 import { WASMSimulator } from './providers/acvm_wasm.js';
 import { AcirSimulator } from './simulator.js';
 
diff --git a/yarn-project/simulator/src/public/avm/avm_simulator.test.ts b/yarn-project/simulator/src/public/avm/avm_simulator.test.ts
index a50aa55729ab..b5044f151dfe 100644
--- a/yarn-project/simulator/src/public/avm/avm_simulator.test.ts
+++ b/yarn-project/simulator/src/public/avm/avm_simulator.test.ts
@@ -75,10 +75,10 @@ import {
 import { encodeToBytecode } from './serialization/bytecode_serialization.js';
 import { Opcode } from './serialization/instruction_serialization.js';
 import {
+  mockCheckNullifierExists,
   mockGetBytecodeCommitment,
   mockGetContractClass,
   mockGetContractInstance,
-  mockGetNullifierIndex,
   mockL1ToL2MessageExists,
   mockNoteHashCount,
   mockNoteHashExists,
@@ -626,7 +626,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         const bytecode = getAvmTestContractBytecode('nullifier_exists');
 
         if (exists) {
-          mockGetNullifierIndex(treesDB, leafIndex, siloedNullifier0);
+          mockCheckNullifierExists(treesDB, true, siloedNullifier0);
         }
 
         const results = await new AvmSimulator(context).executeBytecode(bytecode);
@@ -892,9 +892,9 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         mockGetContractInstance(contractsDB, contractInstanceWithAddress);
         mockGetContractInstance(contractsDB, contractInstanceWithAddress);
         mockGetContractInstance(contractsDB, contractInstanceWithAddress);
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstanceWithAddress.address));
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstanceWithAddress.address));
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstanceWithAddress.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstanceWithAddress.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstanceWithAddress.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstanceWithAddress.address));
 
         const bytecode = getAvmTestContractBytecode('test_get_contract_instance');
 
@@ -930,7 +930,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
         const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
         mockGetContractInstance(contractsDB, contractInstance);
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstance.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstance.address));
 
         const nestedTrace = mock<PublicSideEffectTraceInterface>();
         mockTraceFork(trace, nestedTrace);
@@ -951,7 +951,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
         mockGetContractInstance(contractsDB, contractInstance);
         mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstance.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstance.address));
 
         const nestedTrace = mock<PublicSideEffectTraceInterface>();
         mockTraceFork(trace, nestedTrace);
@@ -975,7 +975,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
         const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
         mockGetContractInstance(contractsDB, contractInstance);
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstance.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstance.address));
 
         mockTraceFork(trace);
 
@@ -994,7 +994,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
         const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
         mockGetContractInstance(contractsDB, contractInstance);
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstance.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstance.address));
 
         const nestedTrace = mock<PublicSideEffectTraceInterface>();
         mockTraceFork(trace, nestedTrace);
@@ -1021,7 +1021,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
         const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
         mockGetContractInstance(contractsDB, contractInstance);
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstance.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstance.address));
 
         mockTraceFork(trace);
 
@@ -1043,7 +1043,7 @@ describe('AVM simulator: transpiled Noir contracts', () => {
         mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
         const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
         mockGetContractInstance(contractsDB, contractInstance);
-        mockGetNullifierIndex(treesDB, await siloAddress(contractInstance.address));
+        mockCheckNullifierExists(treesDB, true, await siloAddress(contractInstance.address));
 
         mockTraceFork(trace);
 
diff --git a/yarn-project/simulator/src/public/avm/opcodes/accrued_substate.test.ts b/yarn-project/simulator/src/public/avm/opcodes/accrued_substate.test.ts
index a1aa53c41eaf..b2e24d127537 100644
--- a/yarn-project/simulator/src/public/avm/opcodes/accrued_substate.test.ts
+++ b/yarn-project/simulator/src/public/avm/opcodes/accrued_substate.test.ts
@@ -12,7 +12,7 @@ import { Field, Uint8, Uint32 } from '../avm_memory_types.js';
 import { InstructionExecutionError, StaticCallAlterationError } from '../errors.js';
 import { initContext, initExecutionEnvironment, initPersistableStateManager } from '../fixtures/index.js';
 import {
-  mockGetNullifierIndex,
+  mockCheckNullifierExists,
   mockL1ToL2MessageExists,
   mockNoteHashCount,
   mockNoteHashExists,
@@ -159,7 +159,7 @@ describe('Accrued Substate', () => {
         const addressOffset = 1;
 
         if (exists) {
-          mockGetNullifierIndex(treesDB, leafIndex, value0);
+          mockCheckNullifierExists(treesDB, true, value0);
         }
 
         context.machineState.memory.set(value0Offset, new Field(value0)); // nullifier
@@ -210,7 +210,7 @@ describe('Accrued Substate', () => {
     });
 
     it('Nullifier collision reverts (nullifier exists in host state)', async () => {
-      mockGetNullifierIndex(treesDB, leafIndex); // db will say that nullifier already exists
+      mockCheckNullifierExists(treesDB, true, leafIndex);
       context.machineState.memory.set(value0Offset, new Field(value0));
       await expect(new EmitNullifier(/*indirect=*/ 0, /*offset=*/ value0Offset).execute(context)).rejects.toThrow(
         new InstructionExecutionError(
diff --git a/yarn-project/simulator/src/public/avm/opcodes/external_calls.test.ts b/yarn-project/simulator/src/public/avm/opcodes/external_calls.test.ts
index 4841f4bb4da7..045e71ad5005 100644
--- a/yarn-project/simulator/src/public/avm/opcodes/external_calls.test.ts
+++ b/yarn-project/simulator/src/public/avm/opcodes/external_calls.test.ts
@@ -13,10 +13,10 @@ import { initContext, initPersistableStateManager } from '../fixtures/index.js';
 import { encodeToBytecode } from '../serialization/bytecode_serialization.js';
 import { Opcode } from '../serialization/instruction_serialization.js';
 import {
+  mockCheckNullifierExists,
   mockGetBytecodeCommitment,
   mockGetContractClass,
   mockGetContractInstance,
-  mockGetNullifierIndex,
   mockTraceFork,
 } from '../test_utils.js';
 import { EnvironmentVariable, GetEnvVar } from './environment_getters.js';
@@ -128,7 +128,7 @@ describe('External Calls', () => {
       mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
       const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
       mockGetContractInstance(contractsDB, contractInstance);
-      mockGetNullifierIndex(treesDB, contractInstance.address.toField());
+      mockCheckNullifierExists(treesDB, true, contractInstance.address.toField());
 
       const { l2GasLeft: initialL2Gas, daGasLeft: initialDaGas } = context.machineState;
 
@@ -174,14 +174,14 @@ describe('External Calls', () => {
         new Set(/*indirect=*/ 0, /*dstOffset=*/ 1, TypeTag.UINT32, 1).as(Opcode.SET_8, Set.wireFormat8),
         new Return(/*indirect=*/ 0, /*retOffset=*/ 0, /*size=*/ 1),
       ]);
-      mockGetNullifierIndex(treesDB, addr);
+      mockCheckNullifierExists(treesDB, true, addr);
 
       const contractClass = await makeContractClassPublic(0, otherContextInstructionsBytecode);
       mockGetContractClass(contractsDB, contractClass);
       mockGetBytecodeCommitment(contractsDB, await computePublicBytecodeCommitment(contractClass.packedBytecode));
       const contractInstance = await makeContractInstanceFromClassId(contractClass.id);
       mockGetContractInstance(contractsDB, contractInstance);
-      mockGetNullifierIndex(treesDB, contractInstance.address.toField());
+      mockCheckNullifierExists(treesDB, true, contractInstance.address.toField());
 
       const { l2GasLeft: initialL2Gas, daGasLeft: initialDaGas } = context.machineState;
 
@@ -252,7 +252,7 @@ describe('External Calls', () => {
       ];
 
       const otherContextInstructionsBytecode = encodeToBytecode(otherContextInstructions);
-      mockGetNullifierIndex(treesDB, addr.toFr());
+      mockCheckNullifierExists(treesDB, true, addr.toFr());
 
       const contractClass = await makeContractClassPublic(0, otherContextInstructionsBytecode);
       mockGetContractClass(contractsDB, contractClass);
diff --git a/yarn-project/simulator/src/public/avm/test_utils.ts b/yarn-project/simulator/src/public/avm/test_utils.ts
index 1be367d7cab4..fa05a8fedca0 100644
--- a/yarn-project/simulator/src/public/avm/test_utils.ts
+++ b/yarn-project/simulator/src/public/avm/test_utils.ts
@@ -38,8 +38,8 @@ export function mockNoteHashExists(worldStateDB: PublicTreesDB, _leafIndex: Fr,
   });
 }
 
-export function mockGetNullifierIndex(worldStateDB: PublicTreesDB, leafIndex: Fr, _ignoredValue?: Fr) {
-  (worldStateDB as jest.Mocked<PublicTreesDB>).getNullifierIndex.mockResolvedValue(leafIndex.toBigInt());
+export function mockCheckNullifierExists(worldStateDB: PublicTreesDB, exists: boolean, _ignoredValue?: Fr) {
+  (worldStateDB as jest.Mocked<PublicTreesDB>).checkNullifierExists.mockResolvedValue(exists);
 }
 
 export function mockL1ToL2MessageExists(
diff --git a/yarn-project/simulator/src/common/db_interfaces.ts b/yarn-project/simulator/src/public/db_interfaces.ts
similarity index 52%
rename from yarn-project/simulator/src/common/db_interfaces.ts
rename to yarn-project/simulator/src/public/db_interfaces.ts
index 862fc5556e14..ee177f472587 100644
--- a/yarn-project/simulator/src/common/db_interfaces.ts
+++ b/yarn-project/simulator/src/public/db_interfaces.ts
@@ -1,11 +1,7 @@
-import type { L1_TO_L2_MSG_TREE_HEIGHT } from '@aztec/constants';
 import type { Fr } from '@aztec/foundation/fields';
 import type { FunctionSelector } from '@aztec/stdlib/abi';
 import type { AztecAddress } from '@aztec/stdlib/aztec-address';
 import type { ContractClassPublic, ContractInstanceWithAddress } from '@aztec/stdlib/contract';
-import type { NullifierMembershipWitness } from '@aztec/stdlib/trees';
-
-import type { MessageLoadOracleInputs } from './message_load_oracle_inputs.js';
 
 /**
  * Database interface for providing access to public state.
@@ -62,47 +58,3 @@ export interface PublicContractsDBInterface {
    */
   getDebugFunctionName(contractAddress: AztecAddress, selector: FunctionSelector): Promise<string | undefined>;
 }
-
-/** Database interface for providing access to note hash tree, l1 to l2 message tree, and nullifier tree. */
-export interface CommitmentsDBInterface {
-  /**
-   * Fetches a message from the db, given its key.
-   * @param contractAddress - Address of a contract by which the message was emitted.
-   * @param messageHash - Hash of the message.
-   * @param secret - Secret used to compute a nullifier.
-   * @dev Contract address and secret are only used to compute the nullifier to get non-nullified messages
-   * @returns The l1 to l2 membership witness (index of message in the tree and sibling path).
-   */
-  getL1ToL2MembershipWitness(
-    contractAddress: AztecAddress,
-    messageHash: Fr,
-    secret: Fr,
-  ): Promise<MessageLoadOracleInputs<typeof L1_TO_L2_MSG_TREE_HEIGHT>>;
-
-  /**
-   * @param leafIndex the leaf to look up
-   * @returns The l1 to l2 leaf message hash or undefined if not found.
-   */
-  getL1ToL2MessageHash(leafIndex: bigint): Promise<Fr | undefined>;
-
-  /**
-   * Gets note hash in the note hash tree at the given leaf index.
-   * @param leafIndex - the leaf to look up.
-   * @returns - The note hash at that index. Undefined if leaf index is not found.
-   */
-  getNoteHash(leafIndex: bigint): Promise<Fr | undefined>;
-
-  /**
-   * Gets the index of a nullifier in the nullifier tree.
-   * @param nullifier - The nullifier.
-   * @returns - The index of the nullifier. Undefined if it does not exist in the tree.
-   */
-  getNullifierIndex(nullifier: Fr): Promise<bigint | undefined>;
-
-  /**
-   * Returns a nullifier membership witness for the given nullifier or undefined if not found.
-   * REFACTOR: Same as getL1ToL2MembershipWitness, can be combined with aztec-node method that does almost the same thing.
-   * @param nullifier - Nullifier we're looking for.
-   */
-  getNullifierMembershipWitnessAtLatestBlock(nullifier: Fr): Promise<NullifierMembershipWitness | undefined>;
-}
diff --git a/yarn-project/simulator/src/public/hinting_db_sources.ts b/yarn-project/simulator/src/public/hinting_db_sources.ts
index 4d21fbb4ce67..bab2827a9003 100644
--- a/yarn-project/simulator/src/public/hinting_db_sources.ts
+++ b/yarn-project/simulator/src/public/hinting_db_sources.ts
@@ -38,7 +38,7 @@ import {
 
 import { strict as assert } from 'assert';
 
-import type { PublicContractsDBInterface } from '../common/db_interfaces.js';
+import type { PublicContractsDBInterface } from './db_interfaces.js';
 import { PublicTreesDB } from './public_db_sources.js';
 
 /**
diff --git a/yarn-project/simulator/src/public/index.ts b/yarn-project/simulator/src/public/index.ts
index 24cf9008f7b1..802b80f80720 100644
--- a/yarn-project/simulator/src/public/index.ts
+++ b/yarn-project/simulator/src/public/index.ts
@@ -1,4 +1,4 @@
-export * from '../common/db_interfaces.js';
+export * from './db_interfaces.js';
 export * from './public_tx_simulator/index.js';
 export * from './public_db_sources.js';
 export { PublicProcessor, PublicProcessorFactory } from './public_processor/public_processor.js';
diff --git a/yarn-project/simulator/src/public/public_db_sources.ts b/yarn-project/simulator/src/public/public_db_sources.ts
index f2ccd0e85de9..9f2578d248e5 100644
--- a/yarn-project/simulator/src/public/public_db_sources.ts
+++ b/yarn-project/simulator/src/public/public_db_sources.ts
@@ -28,7 +28,7 @@ import type { PublicDBAccessStats } from '@aztec/stdlib/stats';
 import { MerkleTreeId, NullifierLeaf, PublicDataTreeLeaf, type PublicDataTreeLeafPreimage } from '@aztec/stdlib/trees';
 import type { BlockHeader, StateReference, Tx } from '@aztec/stdlib/tx';
 
-import type { PublicContractsDBInterface, PublicStateDBInterface } from '../common/db_interfaces.js';
+import type { PublicContractsDBInterface, PublicStateDBInterface } from './db_interfaces.js';
 import { TxContractCache } from './tx_contract_cache.js';
 
 /**
@@ -463,7 +463,7 @@ export class PublicTreesDB extends ForwardMerkleTree implements PublicStateDBInt
     return leafValue;
   }
 
-  public async getNullifierIndex(nullifier: Fr): Promise<bigint | undefined> {
+  public async checkNullifierExists(nullifier: Fr): Promise<boolean> {
     const timer = new Timer();
     const lowLeafResult = await this.getPreviousValueIndex(MerkleTreeId.NULLIFIER_TREE, nullifier.toBigInt());
     if (!lowLeafResult) {
@@ -473,14 +473,14 @@ export class PublicTreesDB extends ForwardMerkleTree implements PublicStateDBInt
     await this.getSiblingPath(MerkleTreeId.NULLIFIER_TREE, lowLeafResult.index);
     // TODO(fcarreiro): We need this for the hints. Might move it to the hinting layer.
     await this.getLeafPreimage(MerkleTreeId.NULLIFIER_TREE, lowLeafResult.index);
-    const index = lowLeafResult.alreadyPresent ? lowLeafResult.index : undefined;
+    const exists = lowLeafResult.alreadyPresent;
 
-    this.logger.debug(`[DB] Fetched nullifier index`, {
+    this.logger.debug(`[DB] Checked nullifier exists`, {
       eventName: 'public-db-access',
       duration: timer.ms(),
-      operation: 'get-nullifier-index',
+      operation: 'check-nullifier-exists',
     } satisfies PublicDBAccessStats);
-    return index;
+    return exists;
   }
 
   public async padTree(treeId: MerkleTreeId, leavesToInsert: number): Promise<void> {
diff --git a/yarn-project/simulator/src/public/state_manager/nullifiers.test.ts b/yarn-project/simulator/src/public/state_manager/nullifiers.test.ts
index 8ca8936a94a4..ea9e3b6f77b1 100644
--- a/yarn-project/simulator/src/public/state_manager/nullifiers.test.ts
+++ b/yarn-project/simulator/src/public/state_manager/nullifiers.test.ts
@@ -18,6 +18,7 @@ describe('avm nullifier caching', () => {
     it('Reading a non-existent nullifier works (gets zero & DNE)', async () => {
       const nullifier = new Fr(2);
       // never written!
+      worldStateDB.checkNullifierExists.mockResolvedValue(false);
       const { exists, cacheHit } = await nullifiers.checkExists(nullifier);
       // doesn't exist, not pending, index is zero (non-existent)
       expect(exists).toEqual(false);
@@ -35,9 +36,8 @@ describe('avm nullifier caching', () => {
     });
     it('Existence check works on fallback to host (gets index, exists, not-pending)', async () => {
       const nullifier = new Fr(2);
-      const storedLeafIndex = BigInt(420);
 
-      worldStateDB.getNullifierIndex.mockResolvedValue(storedLeafIndex);
+      worldStateDB.checkNullifierExists.mockResolvedValue(true);
 
       const { exists, cacheHit } = await nullifiers.checkExists(nullifier);
       // exists (in host), not pending, tree index retrieved from host
@@ -95,10 +95,9 @@ describe('avm nullifier caching', () => {
     });
     it('Cant append nullifier that already exist in host', async () => {
       const nullifier = new Fr(2); // same nullifier for both!
-      const storedLeafIndex = BigInt(420);
 
       // Nullifier exists in host
-      worldStateDB.getNullifierIndex.mockResolvedValue(storedLeafIndex);
+      worldStateDB.checkNullifierExists.mockResolvedValue(true);
       // Can't append to cache
       await expect(nullifiers.append(nullifier)).rejects.toThrow(
         `Siloed nullifier ${nullifier} already exists in parent cache or host.`,
diff --git a/yarn-project/simulator/src/public/state_manager/nullifiers.ts b/yarn-project/simulator/src/public/state_manager/nullifiers.ts
index a593d637e07c..7bea704bce23 100644
--- a/yarn-project/simulator/src/public/state_manager/nullifiers.ts
+++ b/yarn-project/simulator/src/public/state_manager/nullifiers.ts
@@ -64,8 +64,8 @@ export class NullifierManager {
       //  `${MerkleTreeId[MerkleTreeId.NULLIFIER_TREE]} low leaf index should always be found (even if target leaf does not exist)`,
       //);
       //existsInTree = leafOrLowLeafIndex.alreadyPresent;
-      const leafIndex = await this.hostNullifiers.getNullifierIndex(siloedNullifier);
-      existsInTree = leafIndex !== undefined;
+      const exists = await this.hostNullifiers.checkNullifierExists(siloedNullifier);
+      existsInTree = exists;
     }
     const exists = cacheHit || existsInTree;
     return Promise.resolve({ exists, cacheHit });
diff --git a/yarn-project/simulator/src/public/state_manager/public_storage.test.ts b/yarn-project/simulator/src/public/state_manager/public_storage.test.ts
index a79017dfd222..b6357c4fe5b5 100644
--- a/yarn-project/simulator/src/public/state_manager/public_storage.test.ts
+++ b/yarn-project/simulator/src/public/state_manager/public_storage.test.ts
@@ -3,7 +3,7 @@ import { AztecAddress } from '@aztec/stdlib/aztec-address';
 
 import { type MockProxy, mock } from 'jest-mock-extended';
 
-import type { PublicStateDBInterface } from '../../common/db_interfaces.js';
+import type { PublicStateDBInterface } from '../db_interfaces.js';
 import { PublicStorage } from './public_storage.js';
 
 describe('avm public storage', () => {
diff --git a/yarn-project/simulator/src/public/state_manager/public_storage.ts b/yarn-project/simulator/src/public/state_manager/public_storage.ts
index e02f5d3099d5..560c80bf2a47 100644
--- a/yarn-project/simulator/src/public/state_manager/public_storage.ts
+++ b/yarn-project/simulator/src/public/state_manager/public_storage.ts
@@ -1,7 +1,7 @@
 import { Fr } from '@aztec/foundation/fields';
 import type { AztecAddress } from '@aztec/stdlib/aztec-address';
 
-import type { PublicStateDBInterface } from '../../common/db_interfaces.js';
+import type { PublicStateDBInterface } from '../db_interfaces.js';
 
 type PublicStorageReadResult = {
   value: Fr;
diff --git a/yarn-project/simulator/src/public/state_manager/state_manager.test.ts b/yarn-project/simulator/src/public/state_manager/state_manager.test.ts
index 4be91091b729..46040f6ddcae 100644
--- a/yarn-project/simulator/src/public/state_manager/state_manager.test.ts
+++ b/yarn-project/simulator/src/public/state_manager/state_manager.test.ts
@@ -9,10 +9,10 @@ import { mock } from 'jest-mock-extended';
 
 import { initPersistableStateManager } from '../avm/fixtures/index.js';
 import {
+  mockCheckNullifierExists,
   mockGetBytecodeCommitment,
   mockGetContractClass,
   mockGetContractInstance,
-  mockGetNullifierIndex,
   mockL1ToL2MessageExists,
   mockNoteHashCount,
   mockNoteHashExists,
@@ -86,12 +86,13 @@ describe('state_manager', () => {
     });
 
     it('checkNullifierExists works for missing nullifiers', async () => {
+      mockCheckNullifierExists(treesDB, false, leafIndex);
       const exists = await persistableState.checkNullifierExists(address, utxo);
       expect(exists).toEqual(false);
     });
 
     it('checkNullifierExists works for existing nullifiers', async () => {
-      mockGetNullifierIndex(treesDB, leafIndex, utxo);
+      mockCheckNullifierExists(treesDB, true, leafIndex);
       const exists = await persistableState.checkNullifierExists(address, utxo);
       expect(exists).toEqual(true);
     });
@@ -128,14 +129,14 @@ describe('state_manager', () => {
       const siloedNullifier = await siloNullifier(ProtocolContractAddress.ContractInstanceDeployer, address.toField());
 
       mockGetContractInstance(contractsDB, contractInstance.withAddress(address));
-      mockGetNullifierIndex(treesDB, leafIndex, utxo);
+      mockCheckNullifierExists(treesDB, true, leafIndex);
 
       await persistableState.getContractInstance(address);
 
       expect(contractsDB.getContractInstance).toHaveBeenCalledTimes(1);
       expect(contractsDB.getContractInstance).toHaveBeenCalledWith(address, /*blockNumber=*/ expect.any(Number));
-      expect(treesDB.getNullifierIndex).toHaveBeenCalledTimes(1);
-      expect(treesDB.getNullifierIndex).toHaveBeenCalledWith(siloedNullifier);
+      expect(treesDB.checkNullifierExists).toHaveBeenCalledTimes(1);
+      expect(treesDB.checkNullifierExists).toHaveBeenCalledWith(siloedNullifier);
     });
     it('Can get undefined contract instance', async () => {
       await persistableState.getContractInstance(address);
@@ -150,7 +151,7 @@ describe('state_manager', () => {
       const contractClass = await makeContractClassPublic();
       contractClass.packedBytecode = bytecode;
 
-      mockGetNullifierIndex(treesDB, leafIndex);
+      mockCheckNullifierExists(treesDB, true, leafIndex);
       mockGetContractInstance(contractsDB, contractInstance.withAddress(address));
       mockGetContractClass(contractsDB, contractClass);
       mockGetBytecodeCommitment(contractsDB, bytecodeCommitment);
diff --git a/yarn-project/simulator/src/public/state_manager/state_manager.ts b/yarn-project/simulator/src/public/state_manager/state_manager.ts
index e9f74a946eb8..d74043124f7b 100644
--- a/yarn-project/simulator/src/public/state_manager/state_manager.ts
+++ b/yarn-project/simulator/src/public/state_manager/state_manager.ts
@@ -252,7 +252,7 @@ export class PublicPersistableStateManager {
     const siloedNullifier = await siloNullifier(contractAddress, nullifier);
 
     if (this.doMerkleOperations) {
-      const exists = (await this.treesDB.getNullifierIndex(siloedNullifier)) !== undefined;
+      const exists = await this.treesDB.checkNullifierExists(siloedNullifier);
       this.log.trace(`Checked siloed nullifier ${siloedNullifier} (exists=${exists})`);
       return Promise.resolve(exists);
     } else {
@@ -282,10 +282,10 @@ export class PublicPersistableStateManager {
     this.log.trace(`Inserting siloed nullifier=${siloedNullifier}`);
 
     if (this.doMerkleOperations) {
-      const index = await this.treesDB.getNullifierIndex(siloedNullifier);
+      const exists = await this.treesDB.checkNullifierExists(siloedNullifier);
 
-      if (index !== undefined) {
-        this.log.verbose(`Siloed nullifier ${siloedNullifier} already present in tree at index ${index}!`);
+      if (exists) {
+        this.log.verbose(`Siloed nullifier ${siloedNullifier} already present in tree!`);
         throw new NullifierCollisionError(
           `Siloed nullifier ${siloedNullifier} already exists in parent cache or host.`,
         );