regex-le-mcp

<p align="center"> <img src="src/assets/images/icon.png" alt="Regex-LE Logo" width="96" height="96"/> </p> <h1 align="center">Regex-LE: Zero Hassle Regex Extraction & Validation</h1> <p align="center"> <b>Find, test, and validate the regex patterns in the current file</b><br/> <i>Literal patterns, RegExp constructors, ReDoS screening</i> </p>

<p align="center"> <a href="https://marketplace.visualstudio.com/items?itemName=nolindnaidoo.regex-le"> <img src="https://img.shields.io/badge/Install%20from-VS%20Code-blue?style=for-the-badge&logo=visualstudiocode" alt="Install from VS Code Marketplace" /> </a> <a href="https://open-vsx.org/extension/OffensiveEdge/regex-le"> <img src="https://img.shields.io/open-vsx/dt/OffensiveEdge/regex-le?style=for-the-badge&label=Open%20VSX&color=blue" alt="Open VSX downloads" /> </a> <a href="https://www.npmjs.com/package/regex-le-mcp"> <img src="https://img.shields.io/npm/v/regex-le-mcp?style=for-the-badge&label=MCP%20server&color=blue&logo=npm" alt="regex-le-mcp on npm" /> </a> <a href="https://letools.dev"> <img src="https://img.shields.io/badge/LE%20Tools-letools.dev-blue?style=for-the-badge" alt="LE Tools" /> </a> </p>

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<p align="center"> <img src="src/assets/images/demo.gif" alt="Regex-LE Demo" style="max-width: 100%; height: auto;" /> </p>

Useful? A star or rating is how other developers find it — ★ GitHub · ★ Marketplace · ★ Open VSX

What it does

Open any file and run one of three commands. Extract lists every regex pattern found in the document. Test (Ctrl+Alt+R / Cmd+Alt+R) runs a found — or manually entered — pattern against the file content and reports matches with real line/column positions and capture groups (named groups included). Validate checks every found pattern for syntax errors and screens it for ReDoS-prone shapes. Works in VS Code and VS Code–based editors like Cursor and VSCodium (installable from Open VSX).

Use it from an AI agent

The same engine runs as an MCP server, so an agent can call it directly instead of you running a command.

Editor	How
VS Code 1.101+	Nothing to install — the extension registers extract_patterns with agent mode
Zed	Regex-LE — pending review
Claude Code	claude mcp add regex-le -- npx -y regex-le-mcp
Cursor, Windsurf, anything else	point it at npx regex-le-mcp

extract_patterns(content, maxResults?)

Returns every pattern with its flags, 1-based position and a ReDoS verdict, so "are any of the regexes in this file dangerous?" is one call rather than two.

The server takes content and returns data — it reads no files and makes no network requests of its own. Published as regex-le-mcp on npm and as io.github.nolindnaidoo/regex-le in the MCP registry.

<details> <summary><b>Configuring it by hand</b> — any host with an MCP config file</summary>

Most hosts read a JSON config. Add one entry:

{
  "mcpServers": {
    "regex-le": {
      "command": "npx",
      "args": ["-y", "regex-le-mcp"]
    }
  }
}

-y skips the install prompt on first run. Pin a version if you would rather not track releases — regex-le-mcp@2.2.1.

Prefer not to go through npx on every launch? Install it once and point at the binary instead:

npm install -g regex-le-mcp

{
  "mcpServers": {
    "regex-le": { "command": "regex-le-mcp" }
  }
}

It speaks MCP over stdio and needs no environment variables, no API key and no configuration of its own. To check it before wiring it into anything:

echo '{"jsonrpc":"2.0","id":1,"method":"tools/list"}' | npx -y regex-le-mcp

That prints the tool list and exits — if you see extract_patterns, the server works.

</details>

What gets extracted

Extraction scans the whole document (any file type), so constructors split across lines are found too:

Form	Example
Literal	/[a-z]+/gi
Constructor	new RegExp('\\d{4}-\\d{2}', 'g') — including multiline
Bare constructor call	RegExp("x|y", "i")

What is deliberately not extracted:

• Division, dates, and filesystem paths (a / b, 10/29/2025, /usr/local/bin): a / preceded by an identifier, number, ), ], ., or another / is not treated as a regex — after keywords like return, it is.
• Candidates that do not compile as JavaScript regexes, or with invalid/duplicate flags.
• Constructor calls whose pattern argument is a variable or template literal (only literal string arguments are visible to a text scanner).

Duplicate pattern+flags pairs are listed once. This is lexing by heuristic, not a full JS parser: a slash inside a string or comment can still be picked up when its context looks expression-like.

ReDoS screening

Validate (and Test, before running a risky pattern) screens for the common catastrophic-backtracking shapes:

• High severity — nested unbounded quantifiers: (a+)+, ([a-z]+)*
• Medium severity — quantified alternation with overlapping branches: (a|ab)+

This is a structural scanner, not an automaton analysis: it cannot prove a pattern safe, only flag the dangerous shapes it recognizes. The reports also include a rough performance score based on execution time relative to input size — treat it as a hint, not a benchmark (memory is not measured).

Commands

Command	Description
Regex-LE: Test Regex (Ctrl+Alt+R / Cmd+Alt+R)	Test a found or entered pattern against the file
Regex-LE: Extract Patterns	List every regex pattern found in the document
Regex-LE: Validate Regex	Syntax + ReDoS report for every found pattern
Regex-LE: Open Settings	Open Regex-LE settings
Regex-LE: Help & Troubleshooting	Built-in documentation

Settings

Setting	Default	Description
regex-le.openResultsSideBySide	true	Open results beside the current editor
regex-le.copyToClipboardEnabled	false	Also copy results to the clipboard
regex-le.notificationsLevel	silent	all = every notification, important = warnings + errors, silent = errors only
regex-le.safety.enabled	true	Guardrails for very large files and outputs
regex-le.safety.fileSizeWarnBytes	1000000	Refuse processing above this file size
regex-le.safety.largeOutputLinesThreshold	50000	Refuse result documents above this line count
regex-le.statusBar.enabled	true	Show the status bar item
regex-le.telemetryEnabled	false	Local-only event log (see Privacy)
regex-le.regex.redosDetectionEnabled	true	ReDoS screening in Test/Validate
regex-le.regex.maxMatchLimit	1000	Cap on matches collected per test (10–10000)

Languages

Twelve languages besides English:

German · Spanish · French · Indonesian · Italian · Japanese · Korean · Portuguese (Brazil) · Russian · Ukrainian · Vietnamese · Chinese (Simplified)

Both halves are covered — the manifest (command titles, setting names and descriptions) and everything shown while the extension runs (notifications, the status bar, quick-picks and prompts). The extension follows VS Code's display language, so it matches whatever the editor is already set to; no setting of its own.

Privacy & security

• No network access. The extension never sends data anywhere. The telemetryEnabled setting only writes events to a local Output Channel you can inspect (Regex-LE Telemetry).
• Testing a pattern the ReDoS screen rates high-severity asks for confirmation first.
• The MCP server holds the same line. It takes content as an argument and returns data: no filesystem access, no network calls, no telemetry. Your agent already has file-read tools, so duplicating them inside the server would add a path-traversal surface for no capability. check:mcp-bundle fails the build if the server ever imports something that could reach either.
• Error notifications redact home directories and credential-shaped fragments.

Development

bun install
bun run build            # esbuild bundle -> dist/extension.js
bun run typecheck        # tsc --noEmit (includes tests)
bun run test             # vitest unit suite
bun run test:integration # real VS Code extension host
bun run lint             # biome
bun run package          # VSIX into release/

Architecture and conventions live in AGENTS.md. Changes are tracked in CHANGELOG.md.

Performance

<!-- performance:start -->

Input	Size	Found	Time	Rate	Scan speed
JS with literals	1.12 MB	25,000	44.19 ms	565,679/sec	25.4 MB/s
JS with constructors	1.27 MB	25,000	41.86 ms	597,268/sec	30.3 MB/s
Source without regexes	1.24 MB	0	18.75 ms	—	66 MB/s

Median of 7 runs after warmup, on Apple M5 Pro, 24 GB RAM, Node 24.3.0. Inputs are generated by scripts/benchmark.ts rather than checked in, so the sizes above are exactly what was measured. Reproduce with bun run benchmark.

These are machine-specific and are not asserted in CI — a benchmark that gates a build only tells you how busy the runner was. <!-- performance:end -->

Testing

<!-- coverage:start -->

Metric	Coverage
Statements	90.66%
Branches	75.89%
Functions	97.36%
Lines	91.16%

133 test cases across 12 files, plus an integration suite that runs in a real VS Code extension host and an end-to-end test that installs the built .vsix into a clean profile.

Generated from coverage/coverage-summary.json by scripts/coverage-readme.js; CI fails if this section drifts from a fresh run. Reproduce with bun run test:coverage. <!-- coverage:end -->

More from the LE Family

Every tool in the family, one page: letools.dev

All ten also ship as MCP servers — npx <name>-mcp gives any agent the same engine.

• String-LE - Extract string values for i18n from JSON, YAML, CSV, TOML, INI, and .env
• Numbers-LE - Extract numeric values from JSON, YAML, CSV, TOML, INI, and .env
• EnvSync-LE - Spot missing keys across your .env files, with a markdown report
• Paths-LE - Extract file paths from JS/TS imports, JSON, HTML, CSS, TOML, CSV, and .env
• Secrets-LE - Detect and sanitize credentials locally, before you commit
• Scrape-LE - Check whether a page is scrapeable before you write the scraper
• Colors-LE - Extract and analyze colors from CSS, SCSS, LESS, Stylus, HTML, JS/TS, and SVG
• URLs-LE - Extract URLs from documentation, configs, and code
• Dates-LE - Extract and analyze dates from logs, configs, and code

Also by nolindnaidoo

Rust

• pixelcoords — Freeze your screen, mark regions, get pixel-exact coordinates and crops pixelcoords.dev · crates.io · docs.rs
• pixelactions — Consume human-verified coordinates, perform the interaction, confirm it landed pixelactions.dev · crates.io · docs.rs

Contact Developer — GitHub · LinkedIn

License

MIT © nolindnaidoo