maskprompt-mcp

An MCP server that gives AI assistants the ability to redact PII (emails, phones, credit cards, SSNs, IPs, common secrets) from text before it leaves the model's control.

Works with Claude Desktop, Cursor, Cline, Windsurf, Zed, and any other MCP client.

Built-in detectors

| Kind | Pattern | |---|---| | EMAIL | RFC-5322-ish addresses | | US_PHONE | US 10-digit and +1 formats | | US_SSN | XXX-XX-XXXX | | IPV4 | dotted quad | | CREDIT_CARD | 13–19-digit candidates that pass Luhn | | AWS_ACCESS_KEY | AKIA… 20-char keys | | GITHUB_TOKEN | ghp_/gho_/ghu_/ghr_/ghs_… | | JWT | three url-safe base64 segments |

Tools exposed

redact

Redact PII in a string. Pick a strategy:

| Strategy | Replacement | When to use | |---|---|---| | tag (default) | <EMAIL> | LLM sees the type but not the value | | hash | <EMAIL:abc12345> (truncated SHA-256) | Stable cross-run redaction without recovery | | fixed | ███████ | Length-preserving | | remove | (empty) | Both type and value gone |

{ "text": "Email me at [email protected] about invoice 4111-1111-1111-1111." }

→

{
  "masked": "Email me at <EMAIL> about invoice <CREDIT_CARD>.",
  "matches": [
    { "kind": "EMAIL", "start": 12, "end": 29, "value": "[email protected]" },
    { "kind": "CREDIT_CARD", "start": 42, "end": 61, "value": "4111-1111-1111-1111" }
  ]
}

find_pii

Same detection as redact, but doesn't rewrite the input — just returns the matches. Useful when an agent wants to decide whether to refuse based on detected PII.

Configure your MCP client

Claude Desktop's claude_desktop_config.json:

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

License

MIT.