Guide: how to make a mod menu for games on Android

Developing custom modifications for mobile games is a complex but exciting process that requires a deep understanding of Android architecture and the principles of operation of game engines. If you are wondering how to make a menu mod for Android games, you are about to dive into the world of reverse engineering, working with bytecode and low-level programming. Creating a functional interface overlaid on top of the game allows you not only to change the values ​​of health or money, but also to control physics, time speed and other hidden parameters.

The basis of any mod is the ability to intercept control of the game and inject your own code into its memory space. This is achieved through the use of special downloaders or modification of the original APK file of the application. Modern tools allow you to automate many routine tasks, but to create a stable and secure product you need to have a clear understanding of how a virtual machine works Dalvik or ART, as well as how the structure of application resources is arranged.

This guide is not a call for copyright infringement or the creation of cheats for online games, which often leads to blocking accounts. Our goal is to explain the technical side of the process of modifying applications for educational purposes. You will learn what tools are needed to analyze binary files, how to decompile a project, find the necessary methods and implement the logic for displaying the user interface there.

Necessary tools and environment preparation

Before you start writing code, you need to prepare your workplace. You will need a powerful computer, preferably with an operating system Windows or Linux, since most specialized utilities are optimized specifically for these platforms. The key element is having it installed Java Development Kit (JDK), since most tools for working with APKs are written in Java and require the correct setting of environment variables.

To analyze and modify files, you will need specialized decompilers. The most popular and powerful solution today is JADX, which allows you to view decompiled code in a convenient graphical interface. To directly make changes to the bytecode and rebuild the project, Apktoolremains an indispensable tool. It works through the command line and allows you to unpack resources and application code for subsequent editing.

• 🛠️ Apktool - the main tool for decompiling and reverse assembling APK files.
• 💻 JADX-GUI - a app for convenient analysis of source code and searching for strings.
• 📱 Android SDK Platform Tools - a set of ADB utilities for debugging and installing applications on the device.
• 📝 Text editor —for example, VS Code or Notepad++ to edit Smali files.

⚠️ Attention: Working with system tools and modifying someone else's code can lead to unstable operation of the device. Always back up important data before experimenting.

You will also need an Android emulator or a real device with USB debugging enabled. Emulators like Genymotion or built into Android Studio allow you to quickly test assemblies without risking your main smartphone. However, some games are protected from running in emulators, so having a physical device running Android is often a prerequisite for final testing.

Analysis of APK structure and search for target methods

The process of creating a mod begins with a deep analysis of the target application. After decompiling the APK file using Apktool you will get many files with the extension .smali. It is an assembly-like language into which Java code is compiled for execution on the Android virtual machine. Understanding the structure of these files is critical to implementing your code.

The first step is to find the key variables that you plan to change. For example, if you want to create a menu to change the amount of gold, you need to find a method responsible for crediting or debiting currency. In JADX this can be done through a search by string (Search Text) by entering the name of the currency or values ​​associated with it. Often, developers encrypt strings or use obfuscation, replacing friendly variable names with meaningless character sets like a.b.c.

Dynamic analysis techniques can be used to simplify searches. Start the game, change the value of a resource (for example, spend 100 coins), and then take a memory dump or use a debugger Frida to trace function calls. This will allow you to accurately determine the memory address or name of the method that processes this action. The found method will become the entry point for your modification.

What is code obfuscation?

Obfuscation is the process of deliberately complicating the source code of a app in order to complicate its analysis and reverse engineering. When obfuscation, the names of classes, methods and variables are replaced with meaningless combinations of letters, comments are removed, and the app logic is confused, while maintaining its functionality.

Once the desired method is found, it is necessary to study its signature and logic of operation. You need to understand what arguments it takes and what it returns. This will be needed to write your own code in the language Smalithat will call this method with changed parameters or replace the return value with the one you need.

Creating a user interface (UI)

One ​​of the most difficult tasks is creating the visual shell of the mod - the very menu that will appear on top of the game. Since you can't simply add new resources to an application without risking the integrity of the signature, the most common technique used is code injection to create the UI programmatically. This means that all buttons, sliders and windows will be created directly in the mod code at runtime.

The standard Android API is usually used to implement the interface. You need to create a class that will be responsible for drawing the window. This class should be inherited from View or FrameLayout and added to the root window of the game activity. To interact with interface elements (pressing buttons, moving a window), you will need event handlers OnClickListener and OnTouchListener.

• 🎨 Software layout —creating interface elements through code, not XML markup.
• 🖱️ Event handlers —logic for responding to clicks and gestures the user.
• 🔄 Rendering cycle —providing constant updating of the state of menu elements.

Interface code is injected into the application entry point. Typically this is a method onCreate of the main activity or a static initialization block. This is where you register your menu class so that it is created immediately after the game starts. It is important to ensure that your menu has a higher display priority than game elements, otherwise the buttons may be invisible or unclickable.

The code for creating a simple button in Smali can look cumbersome due to the specifics of the language, so many developers prefer to write UI logic in Java, compile it into separate .dex files and include them as a library. This approach greatly simplifies the support and development of menu functionality.

Code injection and working with memory

After preparing the interface, you need to connect it with game logic. This is done by injecting calls to your methods into the game code. In Smali files, this looks like inserting new lines of code into existing methods. For example, to implement the Immortality feature, you can find a method that reduces the player's health and replace the instruction to write a new value with an instruction that ignores the change or sets the maximum value.

A more advanced method is to use native libraries. Many modern games are written in an engine Unity and use native libraries .so (files in C/C++ language). To work with them, you need knowledge of ARM assembler or the use of tools like UnityExplorer i Il2CppDumper. These utilities allow you to restore the structure of classes and methods from native code, which opens up access to changing physics, object spawning and other low-level processes.

invoke-virtual {p0, v1}, Lcom/game/player;->setHealth(I)V
Replace the value of v1 with the constant 9999 before calling
const/high16 v1, 0x461c4000 # Example of a float value 9999.0

When working with memory, it is important to consider data types. In Android, the main types (int, float, boolean) take up different numbers of bytes, and incorrect interpretation of the data can lead to application crash. To search for addresses in memory, memory scanners are often used, working on the principle of “searching for a value -> changing a value -> re-searching”, which allows you to narrow the range of addresses to the one you need.

⚠️ Attention: Changing native libraries (.so files) requires knowledge of the processor architecture. An error in one byte can make the application completely inoperable.

Signing the application and installing it on the device

After making all the necessary changes to the code and resources, the application must be compiled back into an APK file. To do this, use the command apktool b in the terminal. However, the resulting file cannot yet be installed on a smartphone, since the digital signature of the original developer was broken during modification.

Android requires that all installed applications be signed with a cryptographic key. For test purposes, you can use a self-signed certificate. The utility Apktool can automatically sign the assembly if jarsigner or apksigneris configured in the system. There are also specialized tools, such as MT Manager or NP Managerthat allow you to sign applications directly on your smartphone in a couple of touches.

Stage	Tool	Action	Result
Decompilation	Apktool	Unpacking APK	Folder with resources and Smali
Editing	Text editor	Inserting code	Modified .smali files
Building	Apktool	Compiling the project	N unsigned APK
Signature	Apksigner / MT Manager	Certificate overlay	Ready to install APK

If you plan to distribute your mod, it's worth considering creating a unique signing key so that users can update the application without losing data. However, for personal needs a standard test key is sufficient. After signing, the file is installed via ADB command adb install -r mod_game.apk or directly through the file manager on the device.

Debugging and troubleshooting

It’s rare when a mod works perfectly the first time. The most common problem is “Force Close” - the application crashes immediately after launch or when you click on the menu button. To diagnose errors, you need to use Logcat —the Android system log, which records all events, warnings and errors that occur in the system.

Connect the device to the computer and run the command adb logcat in the terminal. Launch the modified game and wait for it to crash. In the log you will see a stack trace - a sequence of method calls that led to the error. Look for lines marked FATAL EXCEPTION or Java.lang.NullPointerException. They will point to the specific line in your code where the problem occurred.

Common causes of errors include: accessing a non-existent resource, a data type error when calling a method, a violation of the game flow, or a library version conflict. The fix requires careful analysis of the logic of your code in the context of the original application. Sometimes clearing the application cache or reinstalling a clean version of the game before modifying again helps.

How to find the required method if the names are obfuscated?

If the method names are replaced with a, b, c, search by the call logic. Follow the chain: button in the menu -> click handler -> calling the game method. Search by argument types and return values. It also helps to analyze the strings associated with the action (for example, “Buy”, “Sell”, “Damage”).

Is it safe to install mods on your main smartphone?

Installing modified applications always carries a risk. Malicious code can be inserted into the mod by an attacker. It is recommended to test unknown assemblies on an emulator or a secondary device where there is no important personal data or linked bank cards.

Why did the mod stop working after updating the game?

Game developers regularly update the code, changing method addresses, class structure and protection systems. A mod created for version 1.0 will most likely not be compatible with version 1.1. It is necessary to carry out the analysis again for each new version of the application.

Is it possible to make a mod for an online game?

It is technically possible to change the client part, but in online games, critical data (currency, level, items) is stored on the server. Changing them on the player's device will either not be saved or will be immediately detected by the anti-cheat system, which will lead to account blocking (ban).

What knowledge is needed to create complex mods?

Advanced modding requires knowledge of Java, understanding of the operation of the Android virtual machine, basic skills in working with assembler (Smali/ARM), the ability to read error logs and an understanding of the principles object-oriented programming.