HG Server

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A Model Context Protocol (MCP) server for Mercurial repository interaction, written in Python 3.10+ with AsyncIO.

Features

Core Version Control

• Repository Creation: Create new repositories (hg_init) or clone existing ones (hg_clone)
• Status & Diff: View working directory status (hg_status) and line-by-line changes (hg_diff)
• Commit Management: Add files (hg_add), commit changes (hg_commit), remove files (hg_remove), and amend the last commit (hg_amend)
• Stashing: Temporarily shelve changes (hg_shelve) and restore them (hg_unshelve)
• File Inspection: View file content at any revision (hg_cat) and rename or move files (hg_rename)

Branching & Navigation

• Navigation: Update to any revision, branch, or bookmark (hg_update)
• Named Branches: Create and list permanent Mercurial branches (hg_branch)
• Bookmarks: Manage lightweight, Git-like pointers (hg_bookmark, hg_bookmarks)
• Advanced Topics: WIP feature isolation with lightweight branches (hg_topic, hg_topics, hg_topic_current)
• Phases: Manage changeset phases for safe history rewriting (hg_phases)
• Tags: Create, remove, and list repository tags (hg_tag, hg_tags)

Remote Synchronization

• Push/Pull: Sync changes with remote repositories (hg_push, hg_pull)
• Remote Insights: Preview incoming or outgoing changesets (hg_incoming, hg_outgoing)
• Path Management: List and manage configured remote paths (hg_paths)
• Branch Heads: Identify branch heads across the repository (hg_heads)

History Rewriting & Recovery

• Rebase & Strip: Move changesets (hg_rebase) or permanently remove them (hg_strip)
• Evolve Toolset: Auto-amend (hg_absorb), fold changesets (hg_fold), split changesets (hg_split), uncommit (hg_uncommit), prune (hg_prune), rewind for undo (hg_rewind), edit metadata (hg_metaedit)
• Stack Navigation: Move through topic stacks (hg_next, hg_previous, hg_stack)
• Interactive Editing: Modify a linear series of changesets non-interactively (hg_histedit)
• Graft & Transplant: Copy changesets via merge machinery (hg_graft) or patch-based (hg_transplant)
• Backout: Reverse the effects of earlier changesets (hg_backout)
• Evolve: Track the evolution of rewritten changesets (hg_evolve)

Merge & Conflict Resolution

• Merging: Combine changes from different branches (hg_merge)
• Conflict Management: List and track files with unresolved merge conflicts (hg_resolve)
• Revert: Discard uncommitted changes and restore files to their last committed state (hg_revert)

Repository Inspection & Diagnostics

• Blame/Annotate: Show line-by-line changeset information (hg_annotate)
• Bisect: Binary search for regression-introducing changesets (hg_bisect)
• File Listing: List all tracked files in the current revision (hg_files)
• State Summary: Get a concise summary of the working directory state (hg_summary)
• Integrity & Identity: Verify repository integrity (hg_verify) and identify the current revision (hg_identify)
• Patch Management: Export changesets as patches (hg_export) or import patch files (hg_import)

Technical Features

• Async I/O: Asynchronous command execution for high-performance operations
• Git Integration (hg-git): Automatic detection of Git-backed repos and branch mapping (hg_git)
• HTTP Transports: Streamable HTTP and SSE support for web-based clients (e.g., llama.cpp WebUI)
• Security: Jail path restriction (required for HTTP) and secure API key authentication
• JSON Output: Automatic JSON formatting for 20+ commands for easy machine parsing
• Large File Support: Management of binaries outside normal history (hg_largefiles)
• Diagnostics & Help: List extensions (hg_extensions), config (hg_config), and access built-in help (hg_help)
• Reliability: 349 tests with 87% coverage, using tmpfs on Linux for extremely fast verification
• 62 MCP Tools: Comprehensive coverage of Mercurial 7.1.x standard commands and built-in extensions

Installation

# Clone the repository
git clone <repository-url>
cd hg-mcp

# Create and activate virtual environment
python -m venv .venv
source .venv/bin/activate  # On Windows: .venv\Scripts\activate

# Install in editable mode
pip install -e .

# Optional: Install with performance enhancements
pip install uvloop  # On Unix/macOS
pip install winloop  # On Windows

Usage

Standard Input/Output (stdio) - Default Mode

# Activate your virtual environment first
source .venv/bin/activate  # On Windows: .venv\Scripts\activate
hg-mcp

This starts the MCP server using stdio transport, which can be used with MCP clients like Claude for Desktop, Qwen-Coder, Gemini-CLI, and OpenCode.

HTTP Transport (SSE and/or Streamable HTTP)

For web-based MCP clients like llama.cpp WebUI, you can run the server with HTTP transport:

# SSE only (compatible with llama.cpp WebUI)
hg-mcp --transport sse --port 8000

# Streamable HTTP only
hg-mcp --transport streamable-http --port 8000

# Both SSE and Streamable HTTP on the same server
hg-mcp --transport sse streamable-http --port 8000

Endpoints:

• SSE: http://localhost:8000/sse
• Streamable HTTP: http://localhost:8000/mcp

Options:

• --transport: One or more transport protocols (stdio, sse, streamable-http)
  • Default: stdio
  • Multiple values: --transport sse streamable-http
• --port: Port to listen on (default: 8000)
• --host: Host to bind to (default: 0.0.0.0)
• --api-key: Optional. Enable mandatory API key authentication. When set, clients must provide this key in their request headers.
• --jail: Required for HTTP transports. Restrict repository access to this directory tree for security.
• --mercurial: Optional. Path to the Mercurial (hg) executable. Defaults to hg (resolved from PATH). Example: --mercurial /usr/local/bin/hg

Security Features

When exposing the MCP server over TCP/IP, two security mechanisms are available:

1. Jail Path Restriction (--jail)

Required for all HTTP transports. This restricts repository access to a specific directory tree, preventing unauthorized access to paths outside the jail:

# Restrict access to /home/user/projects and its subdirectories
hg-mcp --transport streamable-http --port 8000 --jail /home/user/projects

2. API Key Authentication (--api-key)

Optional. You can require clients to authenticate by providing a valid API key. When this option is enabled, the server will reject any request that does not include a matching X-API-Key or API-Key header:

# Enable mandatory API key authentication
hg-mcp --transport streamable-http --port 8000 --jail /home/user/projects --api-key your-secret-key

Integration with AI Assistants

To use this MCP server with your AI coding assistant, point to the correct executable path in your virtual environment.

Configuration Examples

Claude Desktop / Qwen-Coder / Gemini-CLI

{
  "mcpServers": {
    "hg-mcp": {
      "command": "/path/to/your/venv/bin/hg-mcp"
    }
  }
}

OpenCode

{
  "mcp": {
    "hg-mcp": {
      "type": "local",
      "command": ["/path/to/your/venv/bin/hg-mcp"],
      "enabled": true
    }
  }
}

Requirements

• Python 3.10+
• Mercurial installed and available in PATH
• MCP-compatible client

Development

Running Tests

# Install development dependencies
pip install -e ".[dev]"

# Run all tests with coverage
./scripts/runtest.sh

Code Quality

# Run linting
./scripts/lint-check-and-fix.sh

# Run type checking
./scripts/type-check.sh

# Run formatter
./scripts/code-format.sh

Acknowledgments

This project is inspired by mcp-server-mercurial.