Regex Engine MCP - Test, Explain & Build Regex Patterns

Regex Engine MCP Server

EN: Build, test, and understand regular expressions using plain language through your AI assistant. 繁中: 用自然語言透過 AI 助手來建立、測試和理解正規表達式。 日本語: AIアシスタントを通じて自然言語で正規表現の作成、テスト、理解ができます。

What is this? Why do I need it?

• Regular expressions are powerful but notoriously hard to write. Most developers Google regex patterns every time they need one. This server lets you describe what you want in plain English -- like "match US phone numbers" -- and it builds a working regex for you.
• Reading someone else's regex feels like decoding hieroglyphics. The explain tool breaks down any regex into a step-by-step, human-readable explanation. No more guessing what ^(?:[a-z0-9]+(?:\.[a-z0-9]+)*)@ actually means.
• Testing regex in a separate tool breaks your workflow. Instead of switching to regex101.com, you can test patterns, extract matches, and do find-and-replace directly inside your AI assistant while you work.

Quick Install

Cursor (One Click)

Claude Desktop

Add to your MCP config file (claude_desktop_config.json):

{
  "mcpServers": {
    "regex-engine": {
      "url": "https://regex-engine-mcp.yagami8095.workers.dev/mcp"
    }
  }
}

Smithery

npx @smithery/cli install @openclaw-ai/regex-engine-mcp

Tools

Tool	What it does	Example prompt
regex_test	Test a regex pattern against text and return all matches with positions	"Test if this string contains a valid email address"
regex_explain	Explain any regex pattern in plain English, step by step	"Explain what this regex does: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$"
regex_build	Build a regex from a natural language description	"Build a regex that matches dates in YYYY-MM-DD format"
regex_replace	Find and replace using regex with capture group support	"Replace all dates from MM/DD/YYYY to YYYY-MM-DD in this text"
regex_extract	Extract all matching substrings from text	"Extract all URLs from this paragraph"

Copy-Paste Examples

Example 1: Build a regex from a description

Just say to your AI: "Build me a regex that matches email addresses and test it against this text: Contact us at [email protected] or [email protected] for help."

Example 2: Understand a regex you found in code

Just say to your AI: "Explain this regex I found in our codebase: (?:(?:\r\n)?[ \t])(?:(?:[-A-Za-z0-9!#$%&'+/=?^_`{|}~]+)"

Example 3: Extract data from unstructured text

Just say to your AI: "Extract all phone numbers from this text: Call us at (555) 123-4567 or 800-555-0199. International: +44 20 7946 0958"

Plans

Plan	Cost	Calls
Free	$0	20/day
Pro	$29/mo	50,000/month

FAQ

Q: Do I need to install anything? A: No. This runs on Cloudflare Workers. Add the URL to your AI client's MCP config and you are ready. No dependencies, no API keys, no setup.

Q: Which regex flavor does it use? A: JavaScript regex (ECMAScript). This covers 99% of what web developers and general programmers need, including named capture groups, lookaheads, and all standard flags (g, i, m, s, u).

Q: Can it handle complex patterns like recursive matching? A: It handles everything JavaScript regex supports. For truly complex patterns (like balanced parentheses), the build tool will generate the best possible approximation and explain any limitations.

Links

• Main repo
• All 9 servers

License

MIT