Regex Explainer
Explain a regex in plain English and detect catastrophic backtracking risk.
Should I use this
Quality & Safety
Based on automated analysis of tool definitions and protocol compliance.
Context Cost
This is the approximate number of tokens consumed each time the server's tools are loaded into a model's context. Higher counts reduce the attention available for other tasks.
Install
One-Click Install
Add this to your `claude_desktop_config.json` file:
{
"mcpServers": {
"regex-explainer": {
"url": "https://regex-explainer.gumballtools.com/api/mcp"
}
}
}Remote endpoints
https://regex-explainer.gumballtools.com/api/mcpstreamable-httpWhat it can do
Tool inventory
Tools (1)
🟢explain_regex(pattern)
Explain a regular expression in plain English and detect the failure modes that make patterns dangerous rather than merely wrong. Use this whenever a regex needs to be read, reviewed, or verified — and ALWAYS before putting a pattern somewhere it will run against untrusted input. The critical check is catastrophic backtracking: a pattern like (a+)+$ is three characters longer than a safe equivalent, looks harmless, and takes minutes of CPU on a 30-character input that almost matches. That makes it a denial-of-service vector. Whether a pattern is vulnerable depends on whether nested quantifiers can match the same characters in more than one way, which is a structural property that is unreliable to judge by reading. It also flags: missing anchors (an unanchored validator accepts any string that merely CONTAINS a valid value), unescaped dots, character ranges like [A-z] that span punctuation, alternation precedence mistakes where an anchor applies to only one branch, and constructs JavaScript does not support. Input: `pattern` accepts either a bare pattern or a full /pattern/flags literal. JavaScript syntax; PCRE-only constructs are reported as unsupported rather than guessed at. Returns: `summary` (one sentence), `steps` (an ordered walkthrough), `warnings` (each with a code, severity, detail, and fix), `flagNotes`, capture group counts and names, and `hasBlockingIssue` — check that flag first. If the pattern cannot be parsed it returns an error naming the position, rather than a plausible-looking explanation of something else.
Input Schema
{
"type": "object",
"properties": {
"pattern": {
"type": "string",
"description": "A JavaScript regular expression, either bare (\"^\\d+$\") or as a full literal (\"/^\\d+$/gi\"). Up to 2000 characters."
}
},
"required": [
"pattern"
],
"$schema": "https://json-schema.org/draft/2020-12/schema"
}Community
Evidence