Guardrail

Runtime security enforcement for AI-generated and hand-written application code.

Guardrail sits between your app and the outside world — scanning inputs, sanitizing outputs, and failing closed when something looks wrong.

Phase 3: Supply-chain verification, observability metrics, Next.js adapter, optional WASM accelerator.

Quick start

npm install @guardrail/core @guardrail/express

import express from 'express';
import { guardrail, rules } from '@guardrail/express';

const app = express();
app.use(express.json());

app.use(guardrail({
  outputs: {
    redact: ['password', 'ssn', 'token'],
    headers: {
      'X-Content-Type-Options': 'nosniff',
      'X-Frame-Options': 'DENY',
    },
  },
}));

app.post('/api/search',
  guardrail({
    inputs: {
      q: rules.string().sqlSafe().xssSafe().noSecrets().maxLength(100),
    },
  }),
  (req, res) => {
    res.json({ results: [], password: 'will-be-redacted' });
  },
);

app.use(guardrail.errorHandler());
app.listen(3000);

Why Guardrail?

AI coding assistants ship fast — and often ship SQL concatenation, missing auth checks, and secrets in logs. Guardrail adds a transparent, zero-config-friendly security layer so those mistakes are blocked at runtime instead of becoming incidents.

Features (Phase 3)

Module	Package	Status
Input scanner	@guardrail/core / ./input	Done
Output sanitizer	@guardrail/core / ./output	Done
Behavior policies	@guardrail/core / ./policies	Done
AI code detector	@guardrail/core / ./ai-detector	Done
Supply chain verifier	@guardrail/core/supply-chain	Done
Observability metrics	@guardrail/core/observability	Done
Express adapter	@guardrail/express	Done
Fastify adapter	@guardrail/fastify	Done
Hono adapter	@guardrail/hono	Done
Next.js adapter	@guardrail/next	Done
WASM / JS accelerator	@guardrail/wasm	Done (JS default; Rust optional)

Supply chain (startup / CI)

import { verifyImports } from '@guardrail/core/supply-chain';

const result = await verifyImports({
  checksums: { source: 'package-lock.json', algorithm: 'sha512' },
  behaviorProfile: { childProcess: { allowed: false } },
  threatIntelligence: { blockKnownMalicious: true },
});
if (!result.ok) process.exit(1);

Metrics

import { createMetrics } from '@guardrail/core/observability';

const metrics = createMetrics();
app.get('/metrics', (_req, res) => res.type('text/plain').send(metrics.toPrometheus()));

Input rules

import { rules } from '@guardrail/core';

rules.string().sqlSafe().xssSafe().noSecrets().noPathTraversal().maxLength(100);
rules.uuid();
rules.email();
rules.number().min(0).max(150);
rules.object({ zip: rules.string().matches(/^\d{5}$/) });
rules.array(rules.string()).maxItems(10);
rules.file().maxSize(5_000_000).mimeTypes(['image/png']).noExecutable();

Behavior policies

guardrail({
  policies: [
    {
      name: 'admin-only',
      when: (req) => !!req.path?.startsWith('/api/admin'),
      invariant: (req) => req.user?.role === 'admin',
      onViolation: 'block',
      priority: 10,
    },
  ],
});

AI code detector

import { scanCode } from '@guardrail/core/ai-detector';

const findings = await scanCode({
  entryPoint: './src',
  include: ['**/*.ts'],
  severity: 'medium',
});

Monorepo

packages/core      — zero runtime dependencies
packages/express  — Express middleware
packages/fastify  — Fastify plugin
packages/hono     — Hono middleware
packages/next     — Next.js middleware
packages/wasm     — JS accelerator + optional Rust WASM
docs/
examples/express-basic

npm install
npm run build
npm test
npm run benchmark   # ~0.01ms mean for <1KB validateInputs on this machine

Security principles

• Fail closed — errors default to block, not allow
• No eval — library never uses eval or new Function
• Prototype-safe — null-prototype objects for scratch maps
• Secrets never logged — detections emit sanitized events only
• Timing-safe compares available in utils for secret equality
• Offline-first supply chain — lockfile checks without network by default

Documentation

• docs/ — guides for rules, policies, AI detector, frameworks, supply-chain, metrics
• SECURITY.md — disclosure process
• CONTRIBUTING.md — local development
• examples/express-basic — runnable demo

License

MIT