Anvil

MCP client tool for testing and debugging MCP servers. Provides both a CLI for quick terminal testing and a web-based inspector for interactive exploration.

Why "Anvil"?

In a forge, the anvil is where you test and shape your tools. Forge Anvil serves the same purpose for MCP servers — it's where you test, debug, and refine your tools during development.

Features

Feature	Description
CLI Interface	Test MCP servers directly from the command line
Web UI	Interactive browser-based inspector for exploring tools
No Build Step	Web UI is a single HTML file with Vue.js — just serve and use
JSON Output	Machine-readable output for scripting and automation

Installation

# Clone the repository
git clone https://github.com/agentic-forge/forge-anvil.git
cd forge-anvil

# Install dependencies
uv sync

CLI Usage

Basic Commands

# Show server info
anvil info --server http://localhost:8000/mcp

# List available tools
anvil list-tools

# Call a tool with arguments
anvil call get_current_weather --arg city=Berlin

# Call with JSON arguments
anvil call get_forecast --json-args '{"city": "Tokyo", "days": 3}'

# Output as JSON (for scripting)
anvil list-tools --json

# List resources and prompts
anvil list-resources
anvil list-prompts

# Check if server is responsive
anvil ping

Environment Variable

Set ANVIL_SERVER to avoid passing --server every time:

export ANVIL_SERVER=http://localhost:8000/mcp
anvil list-tools

Web UI

Launch the interactive inspector:

anvil ui --port 5000

Open http://localhost:5000 in your browser.

Example: Testing mcp-weather

Terminal 1 — Start the MCP server:

cd /path/to/agentic-forge/mcp-servers/mcp-weather
uv sync
uv run python -m forge_mcp_weather
# Server starts at http://localhost:8000/mcp

Terminal 2 — Use Anvil to test:

# Set the server URL
export ANVIL_SERVER=http://localhost:8000/mcp

# Check server info
anvil info

# List available tools
anvil list-tools

# Get current weather
anvil call get_current_weather --arg city=Berlin

# Get weather with imperial units
anvil call get_current_weather --arg city="New York" --arg units=imperial

# Get 5-day forecast
anvil call get_forecast --json-args '{"city": "Tokyo", "days": 5}'

# Get air quality
anvil call get_air_quality --arg city=Beijing

Integration with Forge MCP Servers

Anvil works with any MCP server, but integrates seamlessly with Forge MCP servers built with FastMCP:

# Start any Forge MCP server
uv run python -m forge_mcp_<server_name>

# Test with Anvil
anvil list-tools --server http://localhost:8000/mcp

Use Cases

Scenario	Command
Quick health check	anvil ping
Discover available tools	anvil list-tools
Test a specific tool	anvil call <tool> --arg key=value
Interactive exploration	anvil ui
CI/CD integration	anvil list-tools --json

Links

GitHub Repository