Recaf MCP

「"Turn Recaf into an API that LLMs can call"」

中文版

Recaf 4 MCP bridge — operate a Recaf workspace via MCP protocol for JVM bytecode analysis and editing.

A Java plugin runs inside Recaf exposing a local HTTP API; a Python MCP server turns that API into MCP tools consumable by LLM clients.

Tools · Quick Start · Bytecode Editing · Install

Tools

Every tool below also accepts an optional window argument; see Multiple Recaf Windows.

Recaf Windows

list_recaf_windows switch_recaf_window open_recaf_window

Workspace

get_workspace_info open_workspace close_workspace add_supporting_resource list_supporting_resources fetch_current_class get_selected_text

Classes

get_all_classes get_class_info get_class_source get_bytecode_of_class get_methods_of_class get_fields_of_class get_inner_classes get_annotations_of_class get_raw_class_bytes

Methods

get_method_by_name get_method_bytecode get_method_info

Search

search_classes_by_name search_members_by_name search_strings search_numbers search_instructions

Cross References

get_xrefs_to_class get_xrefs_to_method get_xrefs_to_field get_callers_of_method get_callees_of_method get_overrides_of_method

Refactor

rename_class rename_method rename_field rename_package rename_local_variable apply_mappings

Decompilers

list_decompilers set_active_decompiler decompile_class_with

Inheritance

get_superclasses get_interfaces get_direct_subclasses get_all_subclasses get_implementors

Resources & Export

get_all_file_names get_file_content get_manifest get_strings_from_resources export_workspace get_modified_classes revert_class

Related MCP server: pyghidra-mcp

Bytecode Editing

Full bytecode read/write: instruction-level editing, JASM text assembly, access flag editing, method/field CRUD, try-catch blocks, class byte replacement, workspace export.

Instructions

list_method_instructions get_method_bytecode replace_instruction insert_instruction remove_instruction

Method Body

assemble_method replace_method_body

Access Flags

edit_class_access edit_method_access edit_field_access

Method / Field CRUD

add_method remove_method add_field remove_field

Other

set_try_catch_blocks replace_class_bytes save_workspace

Requirements

• Java 25

• Python 3.10+

• recaf.jar

Quick Start

1. Provide recaf.jar

The build looks for Recaf in this order:

1. RECAF_JAR env var

2. libs/recaf.jar

3. ../recaf/recaf.jar

$env:RECAF_JAR="D:\deobf\recaf\recaf.jar"

2. Build the Plugin

.\gradlew.bat jar

Output: build/libs/recaf-mcp-plugin-0.1.0.jar

3. Install Plugin

Copy the jar to Recaf's plugin cache directory %APPDATA%/Recaf/plugins/ and launch Recaf.

On successful load:

Recaf MCP plugin listening on http://127.0.0.1:8750

4. Install Python Dependencies

pip install -r requirements.txt

5. Start the MCP Server

python recaf_mcp_server.py --http --port 8751

Or use the launcher script:

.\start_recaf_mcp_http.ps1

MCP Config

{
  "mcpServers": {
    "recaf-mcp": {
      "url": "http://127.0.0.1:8751/mcp"
    }
  }
}

Ports

Health check:

Invoke-WebRequest http://127.0.0.1:8750/health

Multiple Recaf Windows

Several Recaf processes can run at once, each with its own jar. Each one loads the plugin, which binds the first free port from 8750; the MCP server finds them all and numbers them in the order it first sees them. A number is never reused while the MCP server runs, so 2:client.jar can not silently turn into a different jar.

Every other tool takes an optional window: "2", "2:client.jar", or a unique part of the jar name. If a jar name is given with the number it must match, so a stale reference is rejected instead of editing the wrong jar.

• With exactly one window open, window can be omitted.

• With several open and no default chosen, a call fails with the list of windows instead of guessing.

• The default set by switch_recaf_window is shared by every client of the MCP server (the HTTP transport has no per-client session). When several agents work in parallel, have each pass window explicitly.

• open_recaf_window starts the new Recaf the same way an open window was started (same java and jar, read from its process). With no window open it uses --recaf-jar, then RECAF_JAR, then libs/recaf.jar.

Windows that still run an older plugin without /instance are found too, but cannot be cloned by open_recaf_window.

Repository Structure

.
├── src/                  # Java plugin source
├── mcp-server/           # Python MCP server
├── libs/                 # recaf.jar goes here
├── recaf_mcp_server.py   # MCP server entry point
├── requirements.txt      # Python dependencies
├── .mcp.json             # Project MCP config
└── README.md

Security

Binding to all interfaces exposes the MCP server with no authentication:

python recaf_mcp_server.py --http --host 0.0.0.0

Use localhost by default, or place it behind a firewall / VPN.