MCPGex

PatzEdi/MCPGex

3.3

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MCPGex is an MCP server designed to assist in the development, testing, and refinement of regex patterns using LLMs.

MCPGex

MCP server for finding, testing and refining regex patterns

MCPGex is an MCP server that allows LLMs to test and validate regex patterns against test cases. It provides a systematic way to develop regex patterns by defining or generating expected outcomes and iteratively testing patterns until all requirements are satisfied.

[!WARNING] MCPGex is still in its early stages.

Index

How it works

  1. Define the goal: You provide what the goal regex pattern should return. The LLM will generate test cases for you.
  2. Test patterns: The LLM can test different regex patterns against all defined test cases to see which ones pass or fail.
  3. Iterate: Based on the results, the LLM can refine the regex pattern until all test cases pass.
  4. Validate: Once all tests pass, you have a regex pattern that works for your specific use cases.

Installation

Go ahead and install through pip:

pip3 install mcpgex

Usage

Running the Server

If you want to start the MCP server:

mcpgex

Configuration

You can also add a configuration. For example, for Claude Desktop, you can have:

{
  "mcpServers": {
    "mcpgex": {
      "command": "python3",
      "args": ["-m", "mcpgex"]
    }
  }
}

Then, you will be able to use the server in these tools without having to run the python script manually!

Available Tools (click to expand)

The server provides four main tools:

1. add_test_case

Add a new test case with an input string and expected match.

Parameters:

  • input_string (required): The text to test against
  • expected_matches (required): The array of substrings that should be extracted/matched
  • description (optional): Description of what this test case validates

Example:

{
  "input_string": "Contact me at john@example.com for details", 
  "expected_matches": ["john@example.com"],
  "description": "Basic email extraction"
}
2. test_regex

Test a regex pattern against all current test cases.

Parameters:

  • pattern (required): The regex pattern to test
  • flags (optional): Regex flags like 'i' (case-insensitive), 'm' (multiline), 's' (dotall)

Example:

{
  "pattern": "[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}",
  "flags": "i"
}
3. get_test_cases

View all currently defined test cases.

4. clear_test_cases

Remove all test cases to start fresh.

Benefits

  • Comprehensive testing: Ensure patterns work across various use cases
  • Iterative improvement: Easy to test and refine patterns
  • Documentation: Test cases serve as examples and documentation
  • Confidence: Know your regex works before deploying it
  • Fully Automated: Give it instructions, let it do the rest

Requirements (installed automatically through pip3)

  • Python 3.8+
  • MCP library (pip3 install mcp)

License

This project is open source under the MIT license. Feel free to use and modify as needed.