DEX Decompiler Online
Decompile Android DEX (Dalvik Executable) files back to Java source code.
How It Works
Upload
Drag and drop your .dex file or click to browse.
Decompile
JADX converts Dalvik bytecode to readable Java source.
Browse
Explore all decompiled Java classes in your browser.
What is a DEX File?
DEX stands for Dalvik Executable. It is the bytecode format used by the Android runtime (originally Dalvik, now ART) to execute application code. When you build an Android app, your Java or Kotlin source code is first compiled to standard Java bytecode (.class files), then converted to DEX format using the dx or d8 tool.
DEX format was designed specifically for mobile devices with limited memory and processing power. Compared to standard Java class files, DEX files are more compact — multiple class files are merged into a single DEX file, sharing string pools, type descriptors, and other constant data to reduce redundancy.
DEX File Structure
A DEX file contains:
- Header — file magic number, checksum, SHA-1 signature, and size information
- String table — all string constants used in the code, shared across all classes
- Type descriptors — class and primitive type references
- Method and field tables — method signatures and field declarations
- Class definitions — the actual class data including method bytecode
- Bytecode — Dalvik instructions for each method
Multi-DEX and the 64K Method Limit
A single DEX file can reference at most 65,536 methods (the 64K limit). This constraint comes from the 16-bit method reference index used in DEX bytecode. Modern apps with many dependencies routinely exceed this limit.
To handle this, Android introduced multi-DEX support. Large apps split their code across multiple DEX files: classes.dex, classes2.dex, classes3.dex, and so on. Each file can be decompiled independently using this tool. If you have the complete APK, consider using the APK decompiler instead, which handles all DEX files together.
When to Use a DEX Decompiler
- Analyzing extracted DEX files — when you have a DEX file extracted from an APK or obtained separately
- Multi-DEX analysis — when examining a specific classes.dex file from a large application
- Malware analysis — when investigating suspicious DEX payloads that may be loaded dynamically
- Dynamic code loading — some apps download and load additional DEX files at runtime
Frequently Asked Questions
What is a DEX file?
A DEX (Dalvik Executable) file contains compiled bytecode for the Android runtime. It is the executable format used inside APK files. Java or Kotlin source code is first compiled to Java bytecode, then converted to DEX format optimized for mobile devices.
What is the difference between DEX and APK?
A DEX file contains only compiled bytecode. An APK is a complete package that includes one or more DEX files along with resources, assets, the manifest, and signing certificates. If you have the full APK, use the APK decompiler instead.
What is multi-DEX?
A single DEX file has a 65,536 method reference limit. Large applications exceed this limit and split their code across multiple DEX files (classes.dex, classes2.dex, etc.). Each DEX file can be decompiled independently.