@adhisang/minecraft-modding-mcp

English | 日本語

Note: This project is entirely vibe-coded — built with AI-assisted development without formal specs.

@adhisang/minecraft-modding-mcp is an MCP server for AI-assisted Minecraft modding workflows, built on the Model Context Protocol. Use it when an agent needs to inspect Minecraft source, resolve mappings, compare versions, analyze mod JARs, validate Mixin, Access Widener, or Access Transformer files, or work with NBT and registry data from an MCP client.

It runs over stdio and works with Claude Desktop, Claude Code, VS Code, Codex CLI, Gemini CLI, and other MCP-capable clients.

37 tools (6 entry + 31 expert) | 7 resources | 4 namespace mappings | SQLite-backed cache

Features

• Source exploration: browse, list, and search decompiled Minecraft source with line-level context
• Mapping-aware symbol work: convert class, field, and method names between obfuscated, mojang, intermediary, and yarn
• Version comparison: compare class signatures, registry entries, and migration-oriented summaries across Minecraft versions
• Mod JAR analysis: read Fabric, Forge, and NeoForge metadata, entrypoints, Mixin configs, dependencies, source, and remap previews
• Project validation: validate Mixin source, .accesswidener files, and Forge/NeoForge Access Transformer files against the target version
• NBT, registry, cache, and diagnostics: patch NBT payloads, inspect generated registry data, and manage cache/runtime state
• MCP resources: expose versions, class source, artifact metadata, and mappings through URI-based resources

Quick Start

Package Users

Requirements:

• Node.js 22+
• Java is only required for remap-mod-jar and decompile or remap flows that need Vineflower or tiny-remapper

Start the server locally:

npx -y @adhisang/minecraft-modding-mcp

Use this same command in MCP client configs. If automatic JAR downloads are blocked in your environment, set MCP_VINEFLOWER_JAR_PATH and MCP_TINY_REMAPPER_JAR_PATH there.

Client Setup

CLI clients can register the package command directly.

Claude Code:

claude mcp add minecraft-modding -- npx -y @adhisang/minecraft-modding-mcp

OpenAI Codex CLI:

codex mcp add minecraft-modding -- npx -y @adhisang/minecraft-modding-mcp

Run claude mcp list or codex mcp list after registration to verify the server is available.

The stdio transport auto-detects newline-delimited and Content-Length framing, so the same server command works across Codex and standard MCP clients.

Claude Desktop

Add the following to your claude_desktop_config.json:

{
  "mcpServers": {
    "minecraft-modding": {
      "command": "npx",
      "args": ["-y", "@adhisang/minecraft-modding-mcp"]
    }
  }
}

VS Code

Add the following to .vscode/mcp.json in your workspace:

{
  "servers": {
    "minecraft-modding": {
      "command": "npx",
      "args": ["-y", "@adhisang/minecraft-modding-mcp"]
    }
  }
}

Gemini CLI

Add the following to ~/.gemini/settings.json:

{
  "mcpServers": {
    "minecraft-modding": {
      "command": "npx",
      "args": ["-y", "@adhisang/minecraft-modding-mcp"]
    }
  }
}

Then run:

/mcp list

Custom Environment

Pass environment variables to override defaults:

{
  "mcpServers": {
    "minecraft-modding": {
      "command": "npx",
      "args": ["-y", "@adhisang/minecraft-modding-mcp"],
      "env": {
        "MCP_CACHE_DIR": "/path/to/custom/cache",
        "MCP_MAPPING_SOURCE_PRIORITY": "maven-first"
      }
    }
  }
}

Start Here

These six top-level workflow tools cover the common paths and return summary-first results. They are the best default starting points for agents and MCP clients.

All six return result.summary first and can include summary.nextActions when there is a clear follow-up step. Pick the tool from the table, then use the examples and reference docs for exact payloads.

Workflow Notes

These notes cover high-frequency decisions during onboarding. For the full pitfall list, exact contracts, migration notes, and environment variables, see docs/tool-reference.md.

• search-class-source defaults to queryMode="auto" and keeps separator queries such as foo.bar, foo_bar, and foo$bar on the indexed path. Use queryMode="literal" for an explicit full substring scan.
• If you do not already have an artifact, prefer subject.kind="workspace" for inspect-minecraft instead of guessing artifact details. When artifact context is the only missing input, a retryable suggestedCall preserves the requested task.
• trace-symbol-lifecycle expects Class.method in symbol. Keep exact overload matching in the separate descriptor field.
• For unobfuscated releases such as 26.1+, check-symbol-exists and analyze-symbol task="exists" validate mojang lookups against runtime bytecode when no mapping graph exists, and return mapping_unavailable when the runtime JAR itself is unreachable.
• analyze-mod and validate-project require structured subject objects and canonical include groups; stale string-subject or domain-include payloads return ERR_INVALID_INPUT with a retryable suggestedCall.
• validate-project task="project-summary" propagates preferProjectVersion=true across discovered Mixin, Access Widener, and Access Transformer checks. If no version can be resolved from the request or gradle.properties, the summary returns recovery guidance instead of guessing.
• validate-mixin and validate-project keep mapping-health lightweight for obfuscated and mojang validation, avoiding full Tiny mapping graph loads unless intermediary or yarn namespaces are requested.
• validate-project task="project-summary" uses a lightweight artifact probe for tasks["minecraft.artifact.resolved"]; it does not decompile Minecraft or rebuild the source index just to report per-probe status. Set VALIDATE_PROJECT_TASKS_OFF=1 to omit the additive tasks field.

Inspect Minecraft source from a version

{
  "tool": "inspect-minecraft",
  "arguments": {
    "task": "class-source",
    "subject": {
      "kind": "class",
      "className": "net.minecraft.server.Main",
      "artifact": {
        "type": "resolve-target",
        "target": {
          "kind": "version",
          "value": "1.21.10"
        }
      }
    }
  }
}

Map or check a symbol

{
  "tool": "analyze-symbol",
  "arguments": {
    "task": "map",
    "subject": {
      "kind": "method",
      "owner": "net.minecraft.server.Main",
      "name": "tickServer"
    },
    "version": "1.21.10",
    "sourceMapping": "mojang",
    "targetMapping": "intermediary",
    "signatureMode": "name-only"
  }
}

Summarize a mod JAR

{
  "tool": "analyze-mod",
  "arguments": {
    "task": "summary",
    "subject": {
      "kind": "jar",
      "jarPath": "/path/to/mymod-1.0.0.jar"
    }
  }
}

Validate a workspace

{
  "tool": "validate-project",
  "arguments": {
    "task": "project-summary",
    "subject": {
      "kind": "workspace",
      "projectPath": "/workspace/modid",
      "discover": ["mixins", "access-wideners", "access-transformers"]
    },
    "preferProjectVersion": true,
    "preferProjectMapping": true
  }
}

Workspace summaries still default to discovering mixins and access wideners. Add "access-transformers" to subject.discover when you want Access Transformer files included in the summary run.

Documentation

• Detailed example requests for copyable payloads and common workflows
• Tool and configuration reference for exact inputs, outputs, resource behavior, environment variables, and migration notes. Start with the Which Tool for Which Question decision table when you are not sure which tool to call.
• 日本語 README for a Japanese onboarding overview

Tool Surface

Start with these top-level workflow tools unless you already know the exact specialized operation you want. The lower-level tools remain available for narrow follow-up work and automation.

Top-Level Workflow Tools

Source Exploration

Tools for browsing Minecraft versions, resolving source artifacts, and reading or searching decompiled source code.

For unobfuscated releases such as 26.1+, mapping="mojang" uses the runtime/decompile path directly and skips Loom source-jar discovery, while intermediary and yarn fall back to obfuscated with a warning.

Version Comparison & Symbol Tracking

Tools for comparing class and registry changes across Minecraft versions and tracing symbol existence over time.

Mapping & Symbols

Tools for converting symbol names between namespaces and checking symbol existence.

Several lookup tools support compact result shaping for shorter responses. See docs/tool-reference.md for defaults and the full per-tool field list.

NBT Utilities

Tools for decoding, patching, and encoding Java Edition NBT binary data using a typed JSON representation.

Mod Analysis

Tools for extracting metadata from mod JARs, decompiling mod source, searching mod code, and remapping mod namespaces.

Validation

Tools for validating Mixin source, Access Widener files, and Forge/NeoForge Access Transformer files against a target Minecraft version. Workspace options let validation use loader/runtime context when a project path is available.

Registry & Diagnostics

Tools for querying generated registry data and inspecting server runtime state.

Batch Lookup

Tools that share one resolved artifact or Minecraft version across a fixed shortlist. Results include one status per item plus an aggregate summary. See Batch lookup contract for failure handling and retry mapping.

Within one MCP server process, batch class lookups that need the same binary fallback share one in-flight source indexing/decompile rebuild for that artifact.

Detailed parameter constraints, migration notes, resource behavior, and the full environment-variable matrix live in docs/tool-reference.md.

Development

Repository requirements:

• Node.js 22+
• pnpm
• Java when running remap or decompile flows locally

Setup and run the repository:

pnpm install
pnpm dev

Build the packaged shape:

pnpm build
pnpm start

Always run:

pnpm check
pnpm test

Run these when relevant:

• pnpm test:manual:stdio-smoke for MCP transport, registration, or manual workflow changes
• pnpm test:manual:package-smoke when checking packaged install and distribution behavior
• pnpm test:perf for search, index, or performance-sensitive changes
• pnpm test:coverage or pnpm test:coverage:lcov for coverage checks (lines=80, branches=70, functions=80)
• pnpm validate for the full local validation suite

License

MIT