io.github.MukundaKatta/regex-test-mcp

Official

by MukundaKatta · JavaScript

Trustworthy JS regex testing. Real offsets, named groups, safe against zero-width loops.

MCP server io.github.MukundaKatta/regex-test-mcp provides trustworthy JavaScript regex testing using the actual JS regex engine to match real semantics. It supports lookahead, anchors, named groups, and Unicode escapes. The server exposes three tools: test_regex, find_all, and replace.

🛠️ Key Features

Uses the real JavaScript regex engine for exact behavior
Tests lookahead, anchors, named groups, and Unicode escapes

🚀 Use Cases

Verify whether a regex pattern matches (vs. relying on assumed behavior)
Confirm group indices and capture results, including nested capture groups
Check replacement outcomes rather than hand-derived edge cases

⚡ Developer Benefits

Avoids mistakes from hallucinated regex behavior
Ensures replace results account for edge-case semantics such as $&

⚠️ Limitations

The provided description does not list additional constraints or configuration options beyond the three tools

packages/regex-test-mcp/README.md1 KBView on GitHub

@mukundakatta/regex-test-mcp

MCP server for trustworthy regex testing. Three tools: test_regex, find_all, replace. All use the actual JS regex engine, so you get exact semantics for lookahead, anchors, named groups, and Unicode escapes.

Why this exists

LLMs reliably hallucinate regex behavior. Common ways they're wrong:

Confidently stating a pattern matches when it doesn't (or vice versa)
Wrong group indices when there are nested capture groups
Forgetting that . excludes newlines without the s flag
Hand-rolling replace results that miss edge cases ($& semantics, named-group syntax)

Routing the actual test through this MCP server avoids all of those.

Tools

Tool	Returns
`test_regex(pattern, text, flags?)`	`{matched, match, start, end, groups, named_groups}` for the first match
`find_all(pattern, text, flags?)`	All non-overlapping matches (always behaves as `g`); zero-width safe
`replace(pattern, text, replacement, flags?)`	New string + `replaced` boolean; supports `$1`, `$<name>`, `$&`

Install — Claude Desktop

json

{
  "mcpServers": {
    "regex-test": { "command": "npx", "args": ["-y", "@mukundakatta/regex-test-mcp"] }
  }
}

Same shape for Cursor / Cline / Windsurf / Zed.

License

MIT OR Apache-2.0.

Install

Add to VS Code Add to Cursor

claude_desktop_config.json