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Mixin is a trait/mixin and bytecode weaving framework for Java using ASM


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Mixin is a trait/mixin framework for Java using ASM and hooking into the runtime classloading process via a set of pluggable built-in or user-provided services. Built-in services currently support Mojang's LegacyLauncher system, though this is deprecated in favour of ModLauncher by cpw, which has greater extensibility and has support for Java 8 and later.


The main documentation for Mixin can be found in the Wiki.

Additional documentation for individual features and annotations can be found in the extensive Javadoc. For additional help use the channel #mixin on the Sponge Discord Server.


Mixin binaries are available via Jenkins and are published to the following maven repositories:


For handling obfuscation tasks, Mixin provides an Annotation Processor which works at compile time to generate obfuscation mappings for your toolchain to apply. If using Gradle 5 or later, annotation processors are no longer automatically loaded from compile configurations and must be specified explicitly via annotationProcessor configurations. For this purpose, Mixin provides "fat jar" artefacts containing all required dependencies via the :processor classifier. For example if your build uses the dependency org.spongepowered:mixin:1.2.3 then your annotationProcessor configuration should specify dependency org.spongepowered:mixin:1.2.3:processor.

If you are using Mixin in a Minecraft Forge project then the MixinGradle plugin can be used to simplify the configuration of the Mixin Annotation Processor. It provides a simple syntax for configuring the Mixin AP for your project, see the MixinGradle README for how to configure MixinGradle.

Integration with Eclipse

When developing using Mixin, you can use the Mixin Annotation Processor within Eclipse to provide context-sensitive errors and warnings to help you more easily troubleshoot your mixins. To do so:

  1. Run the gradle build command to generate the mixin jar
  2. Open the properties of your eclipse project and navigate to Java Compiler -> Annotation Processing -> Factory Path
  3. Check the Enable project specific settings checkbox
  4. Click the Add External JARs button and select the generated mixin jar with the suffix -processor (hint: it should be in Mixin/build/libs)
  5. Navigate up one level to Java Compiler -> Annotation Processing
  6. Check the Enable project specific settings checkbox
  7. Check the Enable annotation processing checkbox
  8. Click the New... button next to the Processor options box
  • Set Key to reobfSrgFile
  • Set Value to the fully-qualified path to the mcp-srg.srg file (the location of the mapping file varies by platform, if you are unsure where to find it please follow the discord link below).
  1. Click OK to apply the changes

Integration with IntelliJ IDEA

Enhanced functionality for working with Mixin in IntelliJ IDEA is available via the Minecraft Development for IntelliJ IDEA plugin developed by DemonWav.

Version History

Specifying the minVersion property in your configurations is extrememly important. The following version history can be used to determine when features were introduced (and sometimes when major bugs are squashed) in order to help you determine which minVersion you should specify.

Version Date Features / Changes
0.8.3 February 2021
  • Added dynamic target selector support and @Desc target selector
  • Added pattern target selector
  • Added more expressive quantifier support to explicit target selectors
  • Facelift and overall improvements to javadoc
0.8.1 (0.8.2) September 2020
  • Hotfix for supporting ModLauncher 7.0
  • Fix critical issue with resolving obfuscated members in inherited interfaces
  • Updated to ASM 7.2
0.8 January 2020
  • Updated to ASM 6.2
  • Support for ModLauncher
  • Added recognition for Java 9 and 10
  • Support for ForgeGradle 3+ tsrg obfuscation tables
  • Configs can now inherit from other configs
  • @Invoke can now be used to expose constructors
  • Dramatically improved context reporting of unexpected applicator and preprocessor exceptions, making it easier to diagnose when an agent chokes on a specific opcode
  • Bug fixes for
    • Calling members of accessor mixins from inside mixin code
    • Incorrect handling of spaces in explicit target declarations
    • Unexpected behaviour when attempting to redirect a ctor
    • Properly detect incompatible accessor overlap and ignore valid ones (don't warn)
    • Interface static accessors now correctly conform target if interface is classloaded before target class
    • Staticness mismatch for accessor correctly detected and reported instead of causing crash
    • Fixed generator and injector errors relating to double-word operands on the stack needing DUP2
    • Fixed issue in LVT generator folded in from FabricMC
    • Fail-fast when a final method is accidentally hidden by a mixin
    • Fix the appearance of stray CallbackInfo instances in local capture injector LVTs
  • Apache Commons-IO Dependency removed
  • Renamed shaded ASM removed
  • Improved resolution of local variables for local variable capture injections
  • @Coerce on callback injectors and redirects can now resolve super interfaces including mixed-in interfaces
0.7.11 July 2018
  • Fixes for 3 minor bugs: handling of maxShiftBy fixed, improved BeforeInvoke permissive search, disable generic signature merging unless decompiler is active.
0.7.10 June 2018
  • Log an error when a mixin class is subject to classloader restrictions
0.7.9 April 2018
  • Allow certain injectors to target mixin methods.
0.7.8 April 2018
  • Bug fixes for member declaration validation, non-wild ctor redirects, and internal errors in Args subclass generator
0.7.7 March 2018
  • Fixes for handling of log message triggers for INIT phase and error when running with unexpected logger configurations
  • Add warnings for invalid slice points and narrowing conversion in ModifyConstant handlers
0.7.6 November 2017
  • Fix inheritance for string system properties
0.7.5 October 2017
  • Add support for @Coerce on redirect injectors.
0.7.4 September 2017
  • Added @Dynamic annotation for decorating mixin elements with dynamically-injected targets.
0.7.3 August 2017
  • Internal changes to provide for support modlauncher and java 9
0.7.2 August 2017
  • Add profiler for inspecting mixin performance.
0.7.1 August 2017
  • Fixes and improvements to the Mixin AP, fixing handling of multi- dimensional arrays and resolving methods in superclasses of derived types of obfuscated classes
  • Add runtime refmap remapping to support using deobfCompile dependencies with different mapping versions.
0.7 July 2017
  • All official binaries are now signed
  • Upgrade to ASM 5.2
  • Add support for inner classes in Mixins
  • Injectors can now have multiple explicit targets
  • @At annotations can now have their own id
  • Add support for using @Overwrite on non-obfuscated methods as a way of verifying that an overwrite target exists
  • Improve support for synthetic bridges, detect conflicting bridge methods
  • Detect and warn of excessive At.Shift.BY values
  • ModifyConstant can now support multiple slices
  • Add allow to injectors to detect over-injection
0.6.15 July 2017
  • Add support for multiple constants in ModifyConstant
  • Add CONSTANT as general-purpose injection point
  • Add support for redirecting array length access in field redirectors
0.6.14 July 2017
  • Add support for using @Coerce on reference types in Callback Injectors to support derived types.
0.6.13 July 2017
  • Add support for conforming visibility of overwrite methods to match target class. Fixes issues where a target class method has been modified by an Access Transformer to have higher visibility
0.6.12 June 2017
  • Add slice argument to @ModifyConstant
  • Add @ModifyArgs injector which can change multiple method call arguments with a single handler.
0.6.11 June 2017
  • Fix handling of @Unique when the same unique method exists in more than one mixin targetting the same class
  • Fix handling of merged lambdas so that lambdas from mixins are applied correctly when lambdas already exist in the target class (both in the original class and when applied by earlier mixins)
0.6.10 May 2017
  • (0.6.9) Minor fix to remove dependence on deprecated helper
  • Respect remap on Mixin for contained @At
  • Require redirectors which occur before call to superctor to be static
0.6.8 February 2017
  • Allow @ModifyConstant to hook implicit zero in comparisons
0.6.7 January 2017
  • Add support for @Redirect on array access
0.6.6 January 2017
  • Allow static methods in accessor mixins in Java 8 and above
0.6.5 January 2017
  • Add support for injector slices
0.6.4 January 2017
  • Allow descriptors on NEW injection points
0.6.3 December 2016
  • SourceDebugExtension support
0.6.2 December 2016
  • Add support for @Pseudo (virtual target) mixins
0.6.1 November 2016
  • Process soft-implements annotations in the AP
0.6 October 2016
  • Accessor Mixin support
0.5.17 October 2016
  • Allow @Redirect injectors to target NEW opcodes for constructor redirection
0.5.16 October 2016
  • Annotation Processor improvements. Support shadows and overrides in multi-target mixins
  • Support pluggable obfuscation environments in AP
0.5.14 September 2016
  • Add async decompilation support
0.5.13 September 2016
  • Add alternative strategy for injecting field initialisers
0.5.10 June 2016
  • Support @Unique on fields
0.5.9 June 2016
  • Hard fail if a required mixin target was already transformed
0.5.8 June 2016
  • Support constraints on injectors
0.5.7 June 2016
  • Add @Unique annotation
0.5.6 May 2016
  • Environment changes, support environment via agents
0.5.5 April 2016
  • Add @ModifyConstant injector
  • Add @Debug annotation
  • Allow static @ModifyArg handlers in instance methods
0.5.4 April 2016
  • Error handlers also receive mixin prepare errors
0.5.3 February 2016
  • Conform injectors
  • Enable hotswapper automatically if agent is active
  • Fix multiple issues with generics in Annotation Processors
0.5.2 February 2016
  • Support ID on injectors
  • Support priority for injectors
0.5.1 February 2016
  • Overhaul injectors, injectors from all mixins now scan before any injectors are actually processed. Makes injectors more deterministic.
0.4.19 February 2016
  • Add support for @Redirect on fields as well as methods
0.4.18 February 2016
  • Add @ModifyLocal injector
0.4.17 January 2016
  • Support ExtraSRGs in Annotation Processor
  • Include constructors in reference map
  • Add @Mutable annotation to suppress @Final warnings
0.4.15 January 2016
  • Include soft targets in refmap
0.4.14 January 2016
  • Add support for interface mixins
0.4.13 January 2016
  • Add @Final annotation
0.4.11 January 2016
  • Add support for injector grouping and config-wide require value
0.4.10 December 2015
  • Runtime remapping support using RemapperChain
  • Ignore class transformers decorated with @Resource
  • Support @reason and @author validation on overwrites
0.4.8 December 2015
  • Annotation Processor improved to support MixinGradle
  • Support multiple target obfuscation environments in refmaps
0.4.6 September 2015
  • Add INIT phase for handling early FML startup
  • Add support for lambdas in mixins
  • Add support for hot code replacement in mixins
  • Improve Java 8 feature support
0.4.4 July 2015
  • Add constraints for overwrites
0.4.3 May 2015
  • Add INVOKE_ASSIGN injection point
  • Support injector callbacks without args
  • Support coercion of covariant parameter types in callbacks
  • Support truncating local-capturing injector handlers
  • Runtime decompilation of exported classes using fernflower
  • Add export filter
0.4 May 2015
  • Shade relocated ASM package and use throughout
0.3.2 April 2015
  • Error handler support
0.3.1 April 2015
  • Annotation Merging
  • Allow Overwrite methods to be aliased
0.3 March 2015
  • Implemented Environments
  • Intrinsic method support
  • Enabled local variable capture
  • Alias support
0.2 March 2015
  • Added supermixin support (mixins inheriting from other mixins)
0.1 January 2015
  • Basic Mixin Support
  • Basic Injector Support
  • Annotation Processor