From 9e7cc2985d7aca79a08f5a1baa3731af120a6442 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Tue, 29 Apr 2025 18:57:11 +0800
Subject: [PATCH 01/10] feat: add monad testnet

---
 packages/controller-utils/src/constants.ts    |  9 +++++
 packages/controller-utils/src/types.ts        |  6 ++++
 .../src/NetworkController.ts                  | 34 +++++++++++++------
 packages/network-controller/src/types.ts      |  5 +--
 4 files changed, 41 insertions(+), 13 deletions(-)

diff --git a/packages/controller-utils/src/constants.ts b/packages/controller-utils/src/constants.ts
index 4bcb6fbe4cc..1547e32e937 100644
--- a/packages/controller-utils/src/constants.ts
+++ b/packages/controller-utils/src/constants.ts
@@ -50,6 +50,7 @@ export const TESTNET_TICKER_SYMBOLS = {
   LINEA_GOERLI: 'LineaETH',
   LINEA_SEPOLIA: 'LineaETH',
   MEGAETH_TESTNET: 'MegaETH',
+  MONAD_TESTNET: 'MON',
 };
 
 /**
@@ -57,6 +58,7 @@ export const TESTNET_TICKER_SYMBOLS = {
  */
 export const BUILT_IN_CUSTOM_NETWORKS_RPC = {
   MEGAETH_TESTNET: 'https://carrot.megaeth.com/rpc',
+  MONAD_TESTNET: 'https://testnet-rpc.monad.xyz',
 };
 
 /**
@@ -112,6 +114,13 @@ export const BUILT_IN_NETWORKS = {
       blockExplorerUrl: BlockExplorerUrl['megaeth-testnet'],
     },
   },
+  [NetworkType['monad-testnet']]: {
+    chainId: ChainId['monad-testnet'],
+    ticker: NetworksTicker['monad-testnet'],
+    rpcPrefs: {
+      blockExplorerUrl: BlockExplorerUrl['monad-testnet'],
+    },
+  },
   [NetworkType.rpc]: {
     chainId: undefined,
     blockExplorerUrl: undefined,
diff --git a/packages/controller-utils/src/types.ts b/packages/controller-utils/src/types.ts
index 00ac2b0ccb4..970d7e7d5d1 100644
--- a/packages/controller-utils/src/types.ts
+++ b/packages/controller-utils/src/types.ts
@@ -18,6 +18,7 @@ export type InfuraNetworkType =
  */
 export const CustomNetworkType = {
   'megaeth-testnet': 'megaeth-testnet',
+  'monad-testnet': 'monad-testnet',
 } as const;
 export type CustomNetworkType =
   (typeof CustomNetworkType)[keyof typeof CustomNetworkType];
@@ -76,6 +77,7 @@ export enum BuiltInNetworkName {
   LineaMainnet = 'linea-mainnet',
   Aurora = 'aurora',
   MegaETHTestnet = 'megaeth-testnet',
+  MonadTestnet = 'monad-testnet',
 }
 
 /**
@@ -92,6 +94,7 @@ export const ChainId = {
   [BuiltInNetworkName.LineaSepolia]: '0xe705', // toHex(59141)
   [BuiltInNetworkName.LineaMainnet]: '0xe708', // toHex(59144)
   [BuiltInNetworkName.MegaETHTestnet]: '0x18c6', // toHex(6342)
+  [BuiltInNetworkName.MonadTestnet]: '0x279f', // toHex(10143)
 } as const;
 export type ChainId = (typeof ChainId)[keyof typeof ChainId];
 
@@ -109,6 +112,7 @@ export enum NetworksTicker {
   'linea-sepolia' = 'LineaETH',
   'linea-mainnet' = 'ETH',
   'megaeth-testnet' = 'MegaETH',
+  'monad-testnet' = 'MON',
   // TODO: Either fix this lint violation or explain why it's necessary to ignore.
   // eslint-disable-next-line @typescript-eslint/naming-convention
   rpc = '',
@@ -122,6 +126,7 @@ export const BlockExplorerUrl = {
   [BuiltInNetworkName.LineaSepolia]: 'https://sepolia.lineascan.build',
   [BuiltInNetworkName.LineaMainnet]: 'https://lineascan.build',
   [BuiltInNetworkName.MegaETHTestnet]: 'https://megaexplorer.xyz',
+  [BuiltInNetworkName.MonadTestnet]: 'https://testnet.monadexplorer.com',
 } as const satisfies Record<BuiltInNetworkType, string>;
 export type BlockExplorerUrl =
   (typeof BlockExplorerUrl)[keyof typeof BlockExplorerUrl];
@@ -134,6 +139,7 @@ export const NetworkNickname = {
   [BuiltInNetworkName.LineaSepolia]: 'Linea Sepolia',
   [BuiltInNetworkName.LineaMainnet]: 'Linea',
   [BuiltInNetworkName.MegaETHTestnet]: 'Mega Testnet',
+  [BuiltInNetworkName.MonadTestnet]: 'Monad Testnet',
 } as const satisfies Record<BuiltInNetworkType, string>;
 export type NetworkNickname =
   (typeof NetworkNickname)[keyof typeof NetworkNickname];
diff --git a/packages/network-controller/src/NetworkController.ts b/packages/network-controller/src/NetworkController.ts
index f151d9e6c62..2df9f281c2e 100644
--- a/packages/network-controller/src/NetworkController.ts
+++ b/packages/network-controller/src/NetworkController.ts
@@ -7,6 +7,7 @@ import { BaseController } from '@metamask/base-controller';
 import type { Partialize } from '@metamask/controller-utils';
 import {
   InfuraNetworkType,
+  CustomNetworkType,
   NetworkType,
   isSafeChainId,
   isInfuraNetworkType,
@@ -15,7 +16,6 @@ import {
   NetworkNickname,
   BUILT_IN_CUSTOM_NETWORKS_RPC,
   BUILT_IN_NETWORKS,
-  BuiltInNetworkName,
 } from '@metamask/controller-utils';
 import type { PollingBlockTrackerOptions } from '@metamask/eth-block-tracker';
 import EthQuery from '@metamask/eth-query';
@@ -723,26 +723,38 @@ function getDefaultCustomNetworkConfigurationsByChainId(): Record<
   Hex,
   NetworkConfiguration
 > {
-  const { ticker, rpcPrefs } =
-    BUILT_IN_NETWORKS[BuiltInNetworkName.MegaETHTestnet];
-  return {
-    [ChainId[BuiltInNetworkName.MegaETHTestnet]]: {
+  return Object.values(CustomNetworkType).reduce<
+    Record<Hex, NetworkConfiguration>
+  >((obj, customNetworkType) => {
+    const chainId = ChainId[customNetworkType];
+    const { ticker, rpcPrefs } =
+      BUILT_IN_NETWORKS[customNetworkType];
+    // It converts client id to upper case and replace '-' with '_'
+    // to match the key in BUILT_IN_CUSTOM_NETWORKS_RPC
+    // e.g. 'megaeth-testnet' to 'MEGAETH_TESTNET'
+    // e.g. 'monad-testnet' to 'MONAD_TESTNET'
+    // TODO: Refactor controller-utils to use the same format as others
+    const rpcEndpointUrlKey = customNetworkType.toUpperCase().replace('-','_') as keyof typeof BUILT_IN_CUSTOM_NETWORKS_RPC;
+    
+    const networkConfiguration: NetworkConfiguration = {
       blockExplorerUrls: [rpcPrefs.blockExplorerUrl],
-      chainId: ChainId[BuiltInNetworkName.MegaETHTestnet],
+      chainId: ChainId[customNetworkType],
       defaultRpcEndpointIndex: 0,
       defaultBlockExplorerUrlIndex: 0,
-      name: NetworkNickname[BuiltInNetworkName.MegaETHTestnet],
+      name: NetworkNickname[customNetworkType],
       nativeCurrency: ticker,
       rpcEndpoints: [
         {
           failoverUrls: [],
-          networkClientId: BuiltInNetworkName.MegaETHTestnet,
+          networkClientId: customNetworkType,
           type: RpcEndpointType.Custom,
-          url: BUILT_IN_CUSTOM_NETWORKS_RPC.MEGAETH_TESTNET,
+          url: BUILT_IN_CUSTOM_NETWORKS_RPC[rpcEndpointUrlKey],
         },
       ],
-    },
-  };
+    };
+
+    return { ...obj, [chainId]: networkConfiguration };
+  }, {});
 }
 
 /**
diff --git a/packages/network-controller/src/types.ts b/packages/network-controller/src/types.ts
index ba243b04993..cac64e6ef22 100644
--- a/packages/network-controller/src/types.ts
+++ b/packages/network-controller/src/types.ts
@@ -1,4 +1,5 @@
-import type { ChainId, InfuraNetworkType } from '@metamask/controller-utils';
+import { ChainId } from '@metamask/controller-utils';
+import type { InfuraNetworkType } from '@metamask/controller-utils';
 import type { BlockTracker as BaseBlockTracker } from '@metamask/eth-block-tracker';
 import type { SafeEventEmitterProvider } from '@metamask/eth-json-rpc-provider';
 import type { Hex } from '@metamask/utils';
@@ -57,4 +58,4 @@ export type NetworkClientConfiguration =
 /**
  * The Chain ID representing the additional networks to be included as default.
  */
-export type AdditionalDefaultNetwork = (typeof ChainId)['megaeth-testnet'];
+export type AdditionalDefaultNetwork = typeof ChainId['megaeth-testnet'] | typeof ChainId['monad-testnet'];

From cabccf73ee3b4d45897edef41fb6c8893bf661b9 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Tue, 29 Apr 2025 19:12:19 +0800
Subject: [PATCH 02/10] chore: lint & change log

---
 packages/controller-utils/CHANGELOG.md               | 11 +++++++++++
 packages/network-controller/CHANGELOG.md             |  1 +
 packages/network-controller/src/NetworkController.ts |  9 +++++----
 packages/network-controller/src/types.ts             |  7 ++++---
 4 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/packages/controller-utils/CHANGELOG.md b/packages/controller-utils/CHANGELOG.md
index b7330ba994c..81e9752e703 100644
--- a/packages/controller-utils/CHANGELOG.md
+++ b/packages/controller-utils/CHANGELOG.md
@@ -7,6 +7,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add Monad Testnet to various constants, enums, and types ([#5724](https://github.com/MetaMask/core/pull/5724))
+  - Add `MONAD_TESTNET` to `TESTNET_TICKER_SYMBOLS`
+  - Add `monad-testnet` to `BUILT_IN_NETWORKS`
+  - Add `MonadTestnet` to `BuiltInNetworkName` enum
+  - Add `monad-testnet` to `ChainId` type
+  - Add `MonadTestnet` to `NetworksTicker` enum
+  - Add `MonadTestnet` to `BlockExplorerUrl` quasi-enum
+  - Add `MonadTestnet` to `NetworkNickname` quasi-enum
+
 ## [11.7.0]
 
 ### Added
diff --git a/packages/network-controller/CHANGELOG.md b/packages/network-controller/CHANGELOG.md
index 9c72afa847f..03857210942 100644
--- a/packages/network-controller/CHANGELOG.md
+++ b/packages/network-controller/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add optional `getBlockTrackerOptions` argument to NetworkController constructor ([#5702](https://github.com/MetaMask/core/pull/5702))
+- Add Monad Testnet as default network ([#5724](https://github.com/MetaMask/core/pull/5724))
 
 ### Changed
 
diff --git a/packages/network-controller/src/NetworkController.ts b/packages/network-controller/src/NetworkController.ts
index 2df9f281c2e..a4ac8cf74bf 100644
--- a/packages/network-controller/src/NetworkController.ts
+++ b/packages/network-controller/src/NetworkController.ts
@@ -727,15 +727,16 @@ function getDefaultCustomNetworkConfigurationsByChainId(): Record<
     Record<Hex, NetworkConfiguration>
   >((obj, customNetworkType) => {
     const chainId = ChainId[customNetworkType];
-    const { ticker, rpcPrefs } =
-      BUILT_IN_NETWORKS[customNetworkType];
+    const { ticker, rpcPrefs } = BUILT_IN_NETWORKS[customNetworkType];
     // It converts client id to upper case and replace '-' with '_'
     // to match the key in BUILT_IN_CUSTOM_NETWORKS_RPC
     // e.g. 'megaeth-testnet' to 'MEGAETH_TESTNET'
     // e.g. 'monad-testnet' to 'MONAD_TESTNET'
     // TODO: Refactor controller-utils to use the same format as others
-    const rpcEndpointUrlKey = customNetworkType.toUpperCase().replace('-','_') as keyof typeof BUILT_IN_CUSTOM_NETWORKS_RPC;
-    
+    const rpcEndpointUrlKey = customNetworkType
+      .toUpperCase()
+      .replace('-', '_') as keyof typeof BUILT_IN_CUSTOM_NETWORKS_RPC;
+
     const networkConfiguration: NetworkConfiguration = {
       blockExplorerUrls: [rpcPrefs.blockExplorerUrl],
       chainId: ChainId[customNetworkType],
diff --git a/packages/network-controller/src/types.ts b/packages/network-controller/src/types.ts
index cac64e6ef22..e656b579a78 100644
--- a/packages/network-controller/src/types.ts
+++ b/packages/network-controller/src/types.ts
@@ -1,5 +1,4 @@
-import { ChainId } from '@metamask/controller-utils';
-import type { InfuraNetworkType } from '@metamask/controller-utils';
+import type { InfuraNetworkType, ChainId } from '@metamask/controller-utils';
 import type { BlockTracker as BaseBlockTracker } from '@metamask/eth-block-tracker';
 import type { SafeEventEmitterProvider } from '@metamask/eth-json-rpc-provider';
 import type { Hex } from '@metamask/utils';
@@ -58,4 +57,6 @@ export type NetworkClientConfiguration =
 /**
  * The Chain ID representing the additional networks to be included as default.
  */
-export type AdditionalDefaultNetwork = typeof ChainId['megaeth-testnet'] | typeof ChainId['monad-testnet'];
+export type AdditionalDefaultNetwork =
+  | (typeof ChainId)['megaeth-testnet']
+  | (typeof ChainId)['monad-testnet'];

From 28cd3de3c91881565893ff1d745b8908cbf0f344 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Wed, 30 Apr 2025 09:47:00 +0800
Subject: [PATCH 03/10] chore: remove testnet ticket

---
 packages/controller-utils/src/constants.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/packages/controller-utils/src/constants.ts b/packages/controller-utils/src/constants.ts
index 1547e32e937..66ef878345a 100644
--- a/packages/controller-utils/src/constants.ts
+++ b/packages/controller-utils/src/constants.ts
@@ -50,7 +50,6 @@ export const TESTNET_TICKER_SYMBOLS = {
   LINEA_GOERLI: 'LineaETH',
   LINEA_SEPOLIA: 'LineaETH',
   MEGAETH_TESTNET: 'MegaETH',
-  MONAD_TESTNET: 'MON',
 };
 
 /**

From 83db5a288dc9e29201e80ccbedb1252f44ebede5 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Fri, 2 May 2025 23:17:05 +0800
Subject: [PATCH 04/10] chore: update type

---
 packages/network-controller/src/types.ts | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/packages/network-controller/src/types.ts b/packages/network-controller/src/types.ts
index e656b579a78..712312a4482 100644
--- a/packages/network-controller/src/types.ts
+++ b/packages/network-controller/src/types.ts
@@ -1,4 +1,8 @@
-import type { InfuraNetworkType, ChainId } from '@metamask/controller-utils';
+import type { 
+  InfuraNetworkType,
+  CustomNetworkType,
+  ChainId
+} from '@metamask/controller-utils';
 import type { BlockTracker as BaseBlockTracker } from '@metamask/eth-block-tracker';
 import type { SafeEventEmitterProvider } from '@metamask/eth-json-rpc-provider';
 import type { Hex } from '@metamask/utils';
@@ -57,6 +61,4 @@ export type NetworkClientConfiguration =
 /**
  * The Chain ID representing the additional networks to be included as default.
  */
-export type AdditionalDefaultNetwork =
-  | (typeof ChainId)['megaeth-testnet']
-  | (typeof ChainId)['monad-testnet'];
+export type AdditionalDefaultNetwork = (typeof ChainId)[keyof typeof  CustomNetworkType];

From eeba78262f97caae490a4367c447124115ad8501 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Fri, 2 May 2025 23:22:38 +0800
Subject: [PATCH 05/10] chore: lint

---
 packages/network-controller/src/types.ts | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/packages/network-controller/src/types.ts b/packages/network-controller/src/types.ts
index 712312a4482..0ec80815333 100644
--- a/packages/network-controller/src/types.ts
+++ b/packages/network-controller/src/types.ts
@@ -1,7 +1,7 @@
-import type { 
+import type {
   InfuraNetworkType,
   CustomNetworkType,
-  ChainId
+  ChainId,
 } from '@metamask/controller-utils';
 import type { BlockTracker as BaseBlockTracker } from '@metamask/eth-block-tracker';
 import type { SafeEventEmitterProvider } from '@metamask/eth-json-rpc-provider';
@@ -61,4 +61,5 @@ export type NetworkClientConfiguration =
 /**
  * The Chain ID representing the additional networks to be included as default.
  */
-export type AdditionalDefaultNetwork = (typeof ChainId)[keyof typeof  CustomNetworkType];
+export type AdditionalDefaultNetwork =
+  (typeof ChainId)[keyof typeof CustomNetworkType];

From d9ad84d8fc4fcf71a233f7390f38cf6a00fe7ff7 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Fri, 2 May 2025 23:48:03 +0800
Subject: [PATCH 06/10] fix: define custom network explicitly

---
 .../src/NetworkController.ts                  | 86 ++++++++++++-------
 packages/network-controller/src/types.ts      |  2 +-
 2 files changed, 56 insertions(+), 32 deletions(-)

diff --git a/packages/network-controller/src/NetworkController.ts b/packages/network-controller/src/NetworkController.ts
index 33207c354ba..8bf41163fdf 100644
--- a/packages/network-controller/src/NetworkController.ts
+++ b/packages/network-controller/src/NetworkController.ts
@@ -728,39 +728,63 @@ function getDefaultCustomNetworkConfigurationsByChainId(): Record<
   Hex,
   NetworkConfiguration
 > {
-  return Object.values(CustomNetworkType).reduce<
-    Record<Hex, NetworkConfiguration>
-  >((obj, customNetworkType) => {
-    const chainId = ChainId[customNetworkType];
-    const { ticker, rpcPrefs } = BUILT_IN_NETWORKS[customNetworkType];
-    // It converts client id to upper case and replace '-' with '_'
-    // to match the key in BUILT_IN_CUSTOM_NETWORKS_RPC
-    // e.g. 'megaeth-testnet' to 'MEGAETH_TESTNET'
-    // e.g. 'monad-testnet' to 'MONAD_TESTNET'
-    // TODO: Refactor controller-utils to use the same format as others
-    const rpcEndpointUrlKey = customNetworkType
-      .toUpperCase()
-      .replace('-', '_') as keyof typeof BUILT_IN_CUSTOM_NETWORKS_RPC;
+  // Create the `networkConfigurationsByChainId` objects explicitly,
+  // Because it is not always guaranteed that the custom networks are included in the
+  // default networks.
+  return {
+    [ChainId['megaeth-testnet']]: getCustomNetworkConfiguration(
+      CustomNetworkType['megaeth-testnet'],
+    ),
+    [ChainId['monad-testnet']]: getCustomNetworkConfiguration(
+      CustomNetworkType['monad-testnet'],
+    ),
+  }
+}
 
-    const networkConfiguration: NetworkConfiguration = {
-      blockExplorerUrls: [rpcPrefs.blockExplorerUrl],
-      chainId: ChainId[customNetworkType],
-      defaultRpcEndpointIndex: 0,
-      defaultBlockExplorerUrlIndex: 0,
-      name: NetworkNickname[customNetworkType],
-      nativeCurrency: ticker,
-      rpcEndpoints: [
-        {
-          failoverUrls: [],
-          networkClientId: customNetworkType,
-          type: RpcEndpointType.Custom,
-          url: BUILT_IN_CUSTOM_NETWORKS_RPC[rpcEndpointUrlKey],
-        },
-      ],
-    };
+/**
+ * Constructs a `NetworkConfiguration` object by `CustomNetworkType`.
+ *
+ * @param customNetworkType - The type of the custom network.
+ * @returns The `NetworkConfiguration` object.
+ */
+function getCustomNetworkConfiguration(customNetworkType:CustomNetworkType): NetworkConfiguration {
+  const chainId = ChainId[customNetworkType];
+  const { ticker, rpcPrefs } = BUILT_IN_NETWORKS[customNetworkType];
+  const rpcEndpointUrl = getCustomNetworkRpcEndpointUrl(chainId);
+
+  return  {
+    blockExplorerUrls: [rpcPrefs.blockExplorerUrl],
+    chainId: ChainId[customNetworkType],
+    defaultRpcEndpointIndex: 0,
+    defaultBlockExplorerUrlIndex: 0,
+    name: NetworkNickname[customNetworkType],
+    nativeCurrency: ticker,
+    rpcEndpoints: [
+      {
+        failoverUrls: [],
+        networkClientId: customNetworkType,
+        type: RpcEndpointType.Custom,
+        url: rpcEndpointUrl,
+      },
+    ],
+  };
+}
 
-    return { ...obj, [chainId]: networkConfiguration };
-  }, {});
+/**
+ * Get the RPC endpoint URL for a custom network by supported chain ID.
+ * 
+ * @param chainId - The chain ID of the custom network.
+ * @returns The RPC endpoint URL.
+ */
+function getCustomNetworkRpcEndpointUrl(chainId: AdditionalDefaultNetwork): string {
+  switch (chainId) {
+    case ChainId['megaeth-testnet']:
+      return BUILT_IN_CUSTOM_NETWORKS_RPC.MEGAETH_TESTNET;
+    case ChainId['monad-testnet']:
+      return BUILT_IN_CUSTOM_NETWORKS_RPC.MONAD_TESTNET;
+    default:
+      throw new Error(`Unsupported chain ID: ${chainId}`);
+  }
 }
 
 /**
diff --git a/packages/network-controller/src/types.ts b/packages/network-controller/src/types.ts
index 0ec80815333..4cdfd3e0a48 100644
--- a/packages/network-controller/src/types.ts
+++ b/packages/network-controller/src/types.ts
@@ -62,4 +62,4 @@ export type NetworkClientConfiguration =
  * The Chain ID representing the additional networks to be included as default.
  */
 export type AdditionalDefaultNetwork =
-  (typeof ChainId)[keyof typeof CustomNetworkType];
+  (typeof ChainId)['megaeth-testnet' | 'monad-testnet'];

From c1f6e4903b5001913b93e19603588af2913ba834 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Fri, 2 May 2025 23:54:32 +0800
Subject: [PATCH 07/10] fix: lint

---
 .../network-controller/src/NetworkController.ts    | 14 +++++++++-----
 packages/network-controller/src/types.ts           | 11 ++++-------
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/packages/network-controller/src/NetworkController.ts b/packages/network-controller/src/NetworkController.ts
index 8bf41163fdf..dce13e9199d 100644
--- a/packages/network-controller/src/NetworkController.ts
+++ b/packages/network-controller/src/NetworkController.ts
@@ -738,7 +738,7 @@ function getDefaultCustomNetworkConfigurationsByChainId(): Record<
     [ChainId['monad-testnet']]: getCustomNetworkConfiguration(
       CustomNetworkType['monad-testnet'],
     ),
-  }
+  };
 }
 
 /**
@@ -747,12 +747,14 @@ function getDefaultCustomNetworkConfigurationsByChainId(): Record<
  * @param customNetworkType - The type of the custom network.
  * @returns The `NetworkConfiguration` object.
  */
-function getCustomNetworkConfiguration(customNetworkType:CustomNetworkType): NetworkConfiguration {
+function getCustomNetworkConfiguration(
+  customNetworkType: CustomNetworkType,
+): NetworkConfiguration {
   const chainId = ChainId[customNetworkType];
   const { ticker, rpcPrefs } = BUILT_IN_NETWORKS[customNetworkType];
   const rpcEndpointUrl = getCustomNetworkRpcEndpointUrl(chainId);
 
-  return  {
+  return {
     blockExplorerUrls: [rpcPrefs.blockExplorerUrl],
     chainId: ChainId[customNetworkType],
     defaultRpcEndpointIndex: 0,
@@ -772,11 +774,13 @@ function getCustomNetworkConfiguration(customNetworkType:CustomNetworkType): Net
 
 /**
  * Get the RPC endpoint URL for a custom network by supported chain ID.
- * 
+ *
  * @param chainId - The chain ID of the custom network.
  * @returns The RPC endpoint URL.
  */
-function getCustomNetworkRpcEndpointUrl(chainId: AdditionalDefaultNetwork): string {
+function getCustomNetworkRpcEndpointUrl(
+  chainId: AdditionalDefaultNetwork,
+): string {
   switch (chainId) {
     case ChainId['megaeth-testnet']:
       return BUILT_IN_CUSTOM_NETWORKS_RPC.MEGAETH_TESTNET;
diff --git a/packages/network-controller/src/types.ts b/packages/network-controller/src/types.ts
index 4cdfd3e0a48..adffecf160a 100644
--- a/packages/network-controller/src/types.ts
+++ b/packages/network-controller/src/types.ts
@@ -1,8 +1,4 @@
-import type {
-  InfuraNetworkType,
-  CustomNetworkType,
-  ChainId,
-} from '@metamask/controller-utils';
+import type { InfuraNetworkType, ChainId } from '@metamask/controller-utils';
 import type { BlockTracker as BaseBlockTracker } from '@metamask/eth-block-tracker';
 import type { SafeEventEmitterProvider } from '@metamask/eth-json-rpc-provider';
 import type { Hex } from '@metamask/utils';
@@ -61,5 +57,6 @@ export type NetworkClientConfiguration =
 /**
  * The Chain ID representing the additional networks to be included as default.
  */
-export type AdditionalDefaultNetwork =
-  (typeof ChainId)['megaeth-testnet' | 'monad-testnet'];
+export type AdditionalDefaultNetwork = (typeof ChainId)[
+  | 'megaeth-testnet'
+  | 'monad-testnet'];

From a77d247d18f25f5ca51a9c4bac35babb35bc9aef Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Sat, 3 May 2025 00:04:52 +0800
Subject: [PATCH 08/10] chore: lint

---
 packages/controller-utils/src/constants.ts    |  8 +++++--
 .../src/NetworkController.ts                  | 22 +------------------
 2 files changed, 7 insertions(+), 23 deletions(-)

diff --git a/packages/controller-utils/src/constants.ts b/packages/controller-utils/src/constants.ts
index 66ef878345a..e7141d62de3 100644
--- a/packages/controller-utils/src/constants.ts
+++ b/packages/controller-utils/src/constants.ts
@@ -56,9 +56,13 @@ export const TESTNET_TICKER_SYMBOLS = {
  * Map of all built-in custom networks to their RPC endpoints.
  */
 export const BUILT_IN_CUSTOM_NETWORKS_RPC = {
+  /**
+   * @deprecated Please use `megaeth-testnet` instead.
+   */
   MEGAETH_TESTNET: 'https://carrot.megaeth.com/rpc',
-  MONAD_TESTNET: 'https://testnet-rpc.monad.xyz',
-};
+  'megaeth-testnet': 'https://carrot.megaeth.com/rpc',
+  'monad-testnet': 'https://testnet-rpc.monad.xyz',
+}
 
 /**
  * Map of all build-in Infura networks to their network, ticker and chain IDs.
diff --git a/packages/network-controller/src/NetworkController.ts b/packages/network-controller/src/NetworkController.ts
index dce13e9199d..b7ddd36f0ee 100644
--- a/packages/network-controller/src/NetworkController.ts
+++ b/packages/network-controller/src/NetworkController.ts
@@ -750,9 +750,8 @@ function getDefaultCustomNetworkConfigurationsByChainId(): Record<
 function getCustomNetworkConfiguration(
   customNetworkType: CustomNetworkType,
 ): NetworkConfiguration {
-  const chainId = ChainId[customNetworkType];
   const { ticker, rpcPrefs } = BUILT_IN_NETWORKS[customNetworkType];
-  const rpcEndpointUrl = getCustomNetworkRpcEndpointUrl(chainId);
+  const rpcEndpointUrl = BUILT_IN_CUSTOM_NETWORKS_RPC[customNetworkType];
 
   return {
     blockExplorerUrls: [rpcPrefs.blockExplorerUrl],
@@ -772,25 +771,6 @@ function getCustomNetworkConfiguration(
   };
 }
 
-/**
- * Get the RPC endpoint URL for a custom network by supported chain ID.
- *
- * @param chainId - The chain ID of the custom network.
- * @returns The RPC endpoint URL.
- */
-function getCustomNetworkRpcEndpointUrl(
-  chainId: AdditionalDefaultNetwork,
-): string {
-  switch (chainId) {
-    case ChainId['megaeth-testnet']:
-      return BUILT_IN_CUSTOM_NETWORKS_RPC.MEGAETH_TESTNET;
-    case ChainId['monad-testnet']:
-      return BUILT_IN_CUSTOM_NETWORKS_RPC.MONAD_TESTNET;
-    default:
-      throw new Error(`Unsupported chain ID: ${chainId}`);
-  }
-}
-
 /**
  * Constructs properties for the NetworkController state whose values will be
  * used if not provided to the constructor.

From a34db78a1be9c4642fdc4cb4044fbe1f3a4f18f9 Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Sat, 3 May 2025 00:06:01 +0800
Subject: [PATCH 09/10] fix: lint

---
 packages/controller-utils/src/constants.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/controller-utils/src/constants.ts b/packages/controller-utils/src/constants.ts
index e7141d62de3..977c15d7b0f 100644
--- a/packages/controller-utils/src/constants.ts
+++ b/packages/controller-utils/src/constants.ts
@@ -62,7 +62,7 @@ export const BUILT_IN_CUSTOM_NETWORKS_RPC = {
   MEGAETH_TESTNET: 'https://carrot.megaeth.com/rpc',
   'megaeth-testnet': 'https://carrot.megaeth.com/rpc',
   'monad-testnet': 'https://testnet-rpc.monad.xyz',
-}
+};
 
 /**
  * Map of all build-in Infura networks to their network, ticker and chain IDs.

From 7aab865a2a6e6578c4a983dc9ef763d7fa0e955b Mon Sep 17 00:00:00 2001
From: Stanley Yuen <102275989+stanleyyconsensys@users.noreply.github.com>
Date: Tue, 6 May 2025 14:27:27 +0800
Subject: [PATCH 10/10] chore: update change log

---
 packages/controller-utils/CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/controller-utils/CHANGELOG.md b/packages/controller-utils/CHANGELOG.md
index 81e9752e703..fea476a9a66 100644
--- a/packages/controller-utils/CHANGELOG.md
+++ b/packages/controller-utils/CHANGELOG.md
@@ -10,8 +10,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add Monad Testnet to various constants, enums, and types ([#5724](https://github.com/MetaMask/core/pull/5724))
-  - Add `MONAD_TESTNET` to `TESTNET_TICKER_SYMBOLS`
   - Add `monad-testnet` to `BUILT_IN_NETWORKS`
+  - Add `monad-testnet` and `megaeth-testnet` to `BUILT_IN_CUSTOM_NETWORKS_RPC`
   - Add `MonadTestnet` to `BuiltInNetworkName` enum
   - Add `monad-testnet` to `ChainId` type
   - Add `MonadTestnet` to `NetworksTicker` enum