@aegis-sdk/fastify

Fastify plugin for scanning LLM chat messages against prompt injection attacks.

Part of the Aegis.js prompt injection defense toolkit.

Installation

npm install @aegis-sdk/fastify @aegis-sdk/core

Quick Start

import Fastify from 'fastify';
import { aegisPlugin } from '@aegis-sdk/fastify';

const app = Fastify();

app.register(aegisPlugin, {
  aegis: { policy: 'strict' },
  routes: ['/api/chat'],
});

app.post('/api/chat', async (request, reply) => {
  const { messages, instance } = request.aegis; // scanned messages
  // pass messages to your LLM
  return { reply: '...' };
});

app.listen({ port: 3000 });

API

aegisPlugin

Fastify plugin that registers a preHandler hook. The hook reads messages from the request body, runs them through aegis.guardInput(), and attaches the safe messages to request.aegis. Returns 403 with violation details if input is blocked.

Register it with app.register(aegisPlugin, options):

| Option | Type | Default | Description | |---|---|---|---| | aegis | AegisConfig \| Aegis | {} | Aegis configuration or pre-constructed instance | | routes | (string \| RegExp)[] | -- | Routes to protect. If omitted, all POST requests are scanned | | methods | string[] | ["POST"] | HTTP methods to scan | | messagesProperty | string | "messages" | Property on the request body to read messages from | | scanStrategy | ScanStrategy | "last-user" | Which messages to scan | | onBlocked | (request, reply, error) => unknown | -- | Custom error handler. Return truthy to take over the response |

Access scan results in your handler via request.aegis, which returns { messages, instance, auditLog }.

aegisStreamTransform(configOrInstance?)

Returns a TransformStream<string, string> that monitors LLM output tokens for injection payloads, PII leaks, and canary token leaks.

guardMessages(aegis, messages, options?)

Scans messages directly without using the plugin. Throws AegisInputBlocked if input is blocked.

Re-exports

Aegis, AegisInputBlocked, AegisSessionQuarantined, AegisSessionTerminated, and all core types are re-exported for convenience.

Learn More

• Documentation
• GitHub

License

MIT