protect

Protect HTTP routes with Arcjet

Use this skill for HTTP route handlers. If there is no request object (tool calls, MCP handlers, queue workers), load @arcjet/skills#guard instead.

Load @arcjet/skills#choose-protections when you need to pick rules. Load @arcjet/skills#cli to get an ARCJET_KEY before writing code.

Checklist

• Language is JS/TS (stop if not)
• Runtime is Node >=22.21.0 <23 || >=24.5.0, Bun ≥ 1.3.0, or Deno stable
• ARCJET_KEY is in the env file (CLI first; do not leave a TODO)
• Shared arcjet() client at module scope, withRule() for extras
• protect() inside each route handler, not middleware
• Rules that should block use mode: "LIVE"
• Client IP comes from trusted ingress, not a copied forwarding header
• Decisions verified with a real request plus CLI or Console

Client

import arcjet, { shield, detectBot } from "@arcjet/next";

export const aj = arcjet({
  key: process.env.ARCJET_KEY!,
  rules: [
    shield({ mode: "LIVE" }),
    detectBot({ mode: "LIVE", allow: ["CATEGORY:SEARCH_ENGINE"] }),
  ],
});

Pick the adapter the app already uses (@arcjet/next, @arcjet/node, @arcjet/fastify, …). Install it with the project's package manager. Do not hand-edit package.json and guess a version.

Omitted mode is DRY_RUN. detectBot requires exactly one of allow or deny. detectPromptInjection takes mode only — no threshold.

One client. withRule() clones share the decision cache. A second arcjet() constructor does not.

Astro is an integration (arcjet:client), not a shared file. Nuxt is a module (#arcjet). NestJS is ArcjetModule + @InjectArcjet(). Bun and Deno wrap fetch with aj.handler() for IP detection, then still call protect(). Hono on Node passes c.env.incoming.

Handler

export async function GET(request: Request) {
  const decision = await aj.protect(request);

  if (decision.isDenied()) {
    return Response.json({ error: "Forbidden" }, { status: 403 });
  }

  return Response.json({ ok: true });
}