guardrails-mcp-server
[](https://opensource.org/licenses/MIT) [](https://modelcontextprotocol.io) [](https://nodejs.org)
MCP server for AI agent security guardrails. Provides input validation, prompt injection detection, PII redaction, output filtering, policy enforcement, rate limiting, and comprehensive audit logging.
Tools
| Tool | Description |
|---|---|
validate_input | Validate and sanitize incoming requests through all guardrail checks |
filter_output | Filter and redact sensitive data (PII, secrets, credentials) from responses |
check_policy | Evaluate a request against security policies (RBAC, resource access, quotas) |
get_audit_logs | Query the audit log with filtering by type, user, time range |
get_stats | Get engine statistics including active users, block rate, request counts |
update_config | Update guardrail configuration at runtime |
Security Features
- Prompt Injection Detection -- 12 regex patterns for jailbreak, DAN mode, system prompt override
- PII Detection and Redaction -- SSN, credit card, email, phone, IP, API keys, AWS keys, JWT, passwords, private keys, connection strings
- Malicious Code Blocking -- eval, exec, subprocess, child_process, shell injection
- Policy Engine -- Block sensitive paths, dangerous tools, unauthenticated destructive ops, URL allowlist, maintenance windows
- Rate Limiting -- Per-user sliding window (configurable requests/minute)
- Audit Logging -- Timestamped events with metrics, log rotation, external handler support
Install
npm install
Configuration
{
"mcpServers": {
"guardrails": {
"type": "stdio",
"command": "node",
"args": ["/path/to/guardrails-mcp-server/index.js"]
}
}
}
Project Structure
src/engine/GuardrailsEngine.js # Core orchestration
src/validators/InputValidator.js # Prompt injection and PII detection
src/filters/OutputFilter.js # Redaction and harmful content blocking
src/policies/PolicyEngine.js # RBAC, quotas, maintenance windows
src/audit/AuditLogger.js # Event logging and metrics