# Regex Explainer (remote · regex-explainer.gumballtools.com)

Explain a regex in plain English and detect catastrophic backtracking risk.

- Trust score: 76/100 (medium)
- Change this week: +4
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-09-25

## Components

- remote · `regex-explainer.gumballtools.com`: 76/100 (this document), [markdown](https://verifymcp.io/servers/com-gumballtools-regex-explainer/api-mcp.md), [page](https://verifymcp.io/servers/com-gumballtools-regex-explainer/api-mcp)

## Channel facts

- Endpoint: `https://regex-explainer.gumballtools.com/api/mcp`
- Transports: `streamable-http`
- Auth: `none`
- Version: `0.1.0`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically against the live server, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-09-25.

- **Endpoint Security**: 63/100
  - The endpoint's TLS certificate is valid, in date, and uses a strong key.
  - Authorisation not fully verified: no authorisation is required to call this server, and 1 tool(s) never declared a destructiveHint. The MCP spec treats an absent hint as destructive by default, so we cannot call this surface safe.
  - HTTPS is enforced; there's no plaintext access path.
  - The HSTS (Strict-Transport-Security) header is present.
  - DNSSEC check failed: this domain isn't protected by DNSSEC.
- **Transport & Reachability**: 100/100
  - Verified streamable-http transport via a live MCP handshake.
- **Schema Quality & AI Usability**: 73/100
  - AI-judged instruction clarity (excellent).
  - Context-footprint check failed: tool/resource definitions use about 360 tokens (~360/item across 1 items; 1 tools + 0 resources), over budget; trim descriptions and params.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 67/100
  - Stability observed for 20 of 30 days with no destabilising changes; credit accrues until the full window elapses.
- **Tool Coverage**: 100/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 100% of tool parameters carry a description.
- **Tool Safety**: 100/100
  - No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.
  - We read all 1 captured tool definition(s), and no name or description among them implies an irreversible operation.
  - An AI judge read all 1 captured unit(s) of tool text and found none that tries to manipulate the model reading it.
- **Capabilities**: 100/100
  - Implements a current MCP spec version (2026-07-28).

## Install

### How do I install the Regex Explainer MCP server?

Regex Explainer is a hosted endpoint at https://regex-explainer.gumballtools.com/api/mcp, so there is nothing to install locally. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.

### Claude

```bash
claude mcp add --transport http com-gumballtools-regex-explainer 'https://regex-explainer.gumballtools.com/api/mcp'
```

### Cursor

```json
{
  "mcpServers": {
    "com-gumballtools-regex-explainer": {
      "url": "https://regex-explainer.gumballtools.com/api/mcp"
    }
  }
}
```

### VS Code

```json
{
  "servers": {
    "com-gumballtools-regex-explainer": {
      "type": "http",
      "url": "https://regex-explainer.gumballtools.com/api/mcp"
    }
  }
}
```

### Codex

```toml
[mcp_servers.com-gumballtools-regex-explainer]
url = "https://regex-explainer.gumballtools.com/api/mcp"
```

### opencode

```json
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "com-gumballtools-regex-explainer": {
      "type": "remote",
      "url": "https://regex-explainer.gumballtools.com/api/mcp",
      "enabled": true
    }
  }
}
```

### OpenClaw

```bash
openclaw mcp add com-gumballtools-regex-explainer --url 'https://regex-explainer.gumballtools.com/api/mcp' --transport streamable-http
```

### Hermes

```yaml
mcp_servers:
  com-gumballtools-regex-explainer:
    url: "https://regex-explainer.gumballtools.com/api/mcp"
```

### Netclaw

```json
{
  "McpServers": {
    "com-gumballtools-regex-explainer": {
      "Transport": "http",
      "Url": "https://regex-explainer.gumballtools.com/api/mcp"
    }
  }
}
```

### Vellum

```bash
assistant mcp add com-gumballtools-regex-explainer -t streamable-http -u 'https://regex-explainer.gumballtools.com/api/mcp'
```

### Other

```json
{
  "mcpServers": {
    "com-gumballtools-regex-explainer": {
      "type": "http",
      "url": "https://regex-explainer.gumballtools.com/api/mcp"
    }
  }
}
```

The mcpServers block is a cross-client convention. Remote transports vary, so check your client's docs.

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-09-25 (score 76, +1)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-09-23 (score 75, +1)

No change was recorded against any check on this day. Stability & Change Management went from 57 to 60. That category is still filling its 30-day observation window: 17 days of observed history at the previous scan, 18 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-21 (score 74, +1)

No change was recorded against any check on this day. Stability & Change Management went from 50 to 53. That category is still filling its 30-day observation window: 15 days of observed history at the previous scan, 16 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-19 (score 73, +1)

No change was recorded against any check on this day. Stability & Change Management went from 43 to 47. That category is still filling its 30-day observation window: 13 days of observed history at the previous scan, 14 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-16 (score 72, +1)

No change was recorded against any check on this day. Stability & Change Management went from 33 to 37. That category is still filling its 30-day observation window: 10 days of observed history at the previous scan, 11 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-14 (score 71, +1)

No change was recorded against any check on this day. Stability & Change Management went from 27 to 30. That category is still filling its 30-day observation window: 8 days of observed history at the previous scan, 9 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-12 (score 70, +1)

No change was recorded against any check on this day. Stability & Change Management went from 20 to 23. That category is still filling its 30-day observation window: 6 days of observed history at the previous scan, 7 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-09-10 (score 69, +1)

No change was recorded against any check on this day. Stability & Change Management went from 13 to 17. That category is still filling its 30-day observation window: 4 days of observed history at the previous scan, 5 at this one. The score rises as the window fills, whether or not the server changes.

## MCP tools (1)

### `explain_regex` (~360 tokens)

Explain a regular expression

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 parameters:

- `pattern` (string, required): A JavaScript regular expression, either bare ("^\d+$") or as a full literal ("/^\d+$/gi"). Up to 2000 characters.

## Diagnostics

Captured diagnostic sections: TLS, DNSSEC, Authorisation, Transports. The full working is on the page: https://verifymcp.io/servers/com-gumballtools-regex-explainer/api-mcp#diagnostics

## Score history

- 2026-09-25: 76
- 2026-09-24: 75
- 2026-09-23: 75
- 2026-09-22: 74
- 2026-09-21: 74
- 2026-09-20: 73
- 2026-09-19: 73
- 2026-09-18: 72
- 2026-09-17: 72
- 2026-09-16: 72
- 2026-09-15: 71
- 2026-09-14: 71
- 2026-09-13: 70
- 2026-09-12: 70
- 2026-09-11: 69
- 2026-09-10: 69
- 2026-09-09: 68
- 2026-09-08: 68
- 2026-09-07: 67
- 2026-09-06: 67
- 2026-09-05: 66

## Common questions

### What is the Regex Explainer MCP server?

Regex Explainer is an MCP server listed in the public MCP registry as com.gumballtools/regex-explainer. Explain a regex in plain English and detect catastrophic backtracking risk. This page covers its hosted endpoint (https://regex-explainer.gumballtools.com/api/mcp).

### Is the Regex Explainer MCP server safe to use?

Regex Explainer scores 76 out of 100 on VerifyMCP. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.

### What tools does the Regex Explainer MCP server expose?

Regex Explainer exposes 1 tool: explain_regex. Their descriptions and schemas cost roughly 360 tokens of context every time the server is loaded.

### Does the Regex Explainer MCP server require authentication?

No. We connected to Regex Explainer without credentials and it answered, so anything it exposes is reachable by anyone who knows the address.

### Is the Regex Explainer MCP server still maintained?

Regex Explainer is still listed as active in the MCP registry. We last reached this channel on 25 September 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.

## Links

- Remote endpoint: https://regex-explainer.gumballtools.com/api/mcp
- Repository: https://github.com/bwalvoord/gumball
- Website: https://regex-explainer.gumballtools.com/
- Changelog RSS feed: https://verifymcp.io/servers/com-gumballtools-regex-explainer/api-mcp.xml
- Changelog JSON feed: https://verifymcp.io/servers/com-gumballtools-regex-explainer/api-mcp.json
- HTML version of this page: https://verifymcp.io/servers/com-gumballtools-regex-explainer/api-mcp