Rexact

io.github.Nicolasmar91Published by GitHub account Nicolasmar91v0.1.2Updated Oct 24, 2026

Verify, explain and audit regexes (ReDoS, engine compatibility) offline.

VerifiedSTDIODesktop onlyDeveloper Tools Security & Monitoring

Server details

Identifier: io.github.Nicolasmar91/rexact-mcp
Transport: STDIO
Runtime: Desktop only
Trust: Verified
Published: Oct 15, 2026

Security note

MCP servers receive tool arguments from a conversation and may perform external actions. Review what a server can do before you enable it, and give it only the access it needs.

The registry verified the GitHub account Nicolasmar91 for this listing. That does not show the account is the product's maker.

SourceWeft's checks cover whether the listing is complete and the endpoint answered; they do not review the server's code or what its tools do.

Add a badge to your README

Show readers this MCP server is listed on SourceWeft. The badge links to this page.

[![Listed on SourceWeft](https://sourceweft.com/badge/mcp/io.github.Nicolasmar91%2Frexact-mcp.svg)](https://sourceweft.com/mcp/io.github.Nicolasmar91%2Frexact-mcp?utm_source=readme&utm_medium=badge)

Overview

AI-generated overview

Local MCP server that lets an assistant verify, explain, ReDoS-audit and check engine compatibility of regular expressions, plus optionally generate regexes.

What you can do: Verify regex patterns against test cases and return a corpus report
Audit patterns for ReDoS risk and get a verdict
Explain a pattern token by token, with a locale option
Check compatibility of a pattern against chosen regex engine targets
Generate a verified pattern from a description and cases (requires an Anthropic API key)
When to use it: Useful when you write or review regular expressions and want an assistant to test them against sample inputs, explain what they match, spot catastrophic backtracking, or confirm they work across different regex engines.
Requirements: Runs locally over stdio, typically launched with npx from the rexact-mcp npm package, so Node.js and network access for the first install are needed. Four of the five tools work offline with no key; the generate_regex tool needs an ANTHROPIC_API_KEY environment variable. An optional self-hosted HTTP mode is also documented.

Before you install

The generate_regex tool sends your description and cases to Anthropic using your own ANTHROPIC_API_KEY, billed to your account. The README states supplied regexes are only run inside a sandboxed worker with a hard timeout, but you are still handing untrusted patterns to a local process.

Installation

In SourceWeft

Open Rexact in the dashboard and add it to a workspace.
Enable the server for the chats that should use its tools.

Desktop only via STDIO. STDIO servers start a local process, so they need the SourceWeft desktop host.

Other MCP clients

Follow the launch instructions in the repository.

README

rexact-mcp

Serveur MCP (Model Context Protocol) pour Rexact — vérification, analyse ReDoS, explication et compatibilité multi-moteurs de regex, adossées à @rexact/core (le même moteur déterministe que le site).

Quatre des cinq outils fonctionnent hors ligne, sans clé API, sans coût :

Outil	Entrée	Sortie
`verify_regex`	pattern, flags, cases	`CorpusReport`
`check_redos`	pattern, flags	`RedosVerdict`
`explain_regex`	pattern, flags, locale	`ExplainToken[]`
`check_compat`	pattern, flags, targets	`CompatIssue[]`
`generate_regex`	description, cases, flavor	motif vérifié — nécessite `ANTHROPIC_API_KEY`

Aucune regex fournie n'est jamais exécutée en dehors d'un bac à sable worker_threads avec timeout dur et terminaison forcée (invariant I2 du dépôt) — jamais un new RegExp().test() direct côté serveur.

Installation locale (transport stdio)

Le plus simple pour un client MCP comme Claude Desktop : coller ce bloc dans sa configuration MCP.

json

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

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

Pour activer generate_regex (facultatif), ajouter votre propre clé Anthropic — c'est votre clé, à votre coût, jamais le quota gratuit du site :

json

{  "mcpServers": {    "rexact": {      "command": "npx",      "args": ["-y", "rexact-mcp"],      "env": {        "ANTHROPIC_API_KEY": "sk-ant-..."      }    }  }}

{  "mcpServers": {    "rexact": {      "command": "npx",      "args": ["-y", "rexact-mcp"],      "env": {        "ANTHROPIC_API_KEY": "sk-ant-..."      }    }  }}

Transport HTTP streamable

Pour héberger le serveur (auto-hébergement, réseau interne) :

Le serveur écoute sur / (POST pour ouvrir une session et envoyer des requêtes, GET pour le flux SSE d'une session existante). L'en-tête mcp-session-id, renvoyé à l'initialisation, identifie la session sur les requêtes suivantes.

Développement

bash

pnpm --filter rexact-mcp dev      # rebuild à chaque changementpnpm --filter rexact-mcp typecheck

pnpm --filter rexact-mcp dev      # rebuild à chaque changementpnpm --filter rexact-mcp typecheck

Liens

Page d'accueil, exemples et installation par client : https://rexact.dev/fr/mcp (EN : https://rexact.dev/en/mcp). Licence : MIT.

Source: apps/mcp/README.md at commit f5237e1

Tools

SourceWeft has not started this package in its sandbox yet, so its tools are not known.

Version history

v0.1.2LatestOct 15, 2026

Score

50% of the applicable checks met

How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.

Reached in the last 30 days25 pts
Keep the endpoint answering the MCP handshake; SourceWeft probes it every 30 days.
Auth declared10 pts
Declare the credential headers in the registry entry, or keep the endpoint answering the probe so its auth can be classified.
Tools listed15 pts
Answer tools/list without a credential, or ship a package that starts in a sandbox without one.
DescriptionRequired15 pts
Logo10 pts
Documentation15 pts
License10 pts