/nitro

Plugins & Lifecycle Hooks

Nitro plugins run once at server startup to extend runtime behavior. They are auto-registered from plugins/ (by filename order) and receive the nitroApp context. Import definePlugin from nitro.

import { definePlugin } from "nitro";

export default definePlugin((nitroApp) => {
  console.log("Nitro starting");
});

v3 renamed defineNitroPlugin → definePlugin. The plugin function itself must be synchronous (return void); the hooks it registers may be async. Register external plugins with the plugins: ["~/plugins/x.ts"] config option.

The nitroApp context

Runtime hooks

Register lifecycle callbacks inside a plugin. hook() returns an unregister function.

import { definePlugin } from "nitro";

export default definePlugin((nitroApp) => {
  nitroApp.hooks.hook("request", (event) => {
    console.log("→", event.path);
  });

  nitroApp.hooks.hook("response", (res, event) => {
    const { pathname } = new URL(event.req.url);
    if (pathname.endsWith(".js")) res.headers.append("Vary", "Origin");
  });

  nitroApp.hooks.hook("close", async () => {
    // clean up DB connections, timers, etc.
  });
});

The request hook is the very first code per request (errors there are captured, not fatal). The response hook runs for every response, including static assets and errors. On shutdown the server waits for pending event.waitUntil tasks.

Error capture

import { definePlugin } from "nitro";

export default definePlugin((nitroApp) => {
  nitroApp.hooks.hook("error", (error, { event, tags }) => {
    console.error(`[${tags?.join(",")}] ${event?.path}`, error);
  });

  // Manually report
  nitroApp.captureError(new Error("startup issue"), { tags: ["startup"] });
});

tags identify the source: "request", "response", "cache", "plugin", "unhandledRejection", "uncaughtException". Process-level unhandled rejections and uncaught exceptions are auto-captured into the error hook.

Notes

• features.runtimeHooks is auto-enabled when at least one plugin exists; force with features.runtimeHooks: true.
• NitroRuntimeHooks is augmentable — presets add platform hooks (e.g. Cloudflare cloudflare:scheduled, cloudflare:email; Vercel vercel:queue).
• useNitroApp, useNitroHooks, and getRouteRules are imported from nitro/app (no auto-imports in v3). Outside plugins, prefer useNitroHooks() over useNitroApp().hooks to guarantee a hooks instance.
• The hook() method returns an unregister function.
• For internal requests to your own server, use serverFetch from nitro (v2 localFetch is gone).

Key Points

• Plugins run once at startup; use them to init resources and register hooks.
• Import definePlugin from nitro (not defineNitroPlugin); useNitroApp/useNitroHooks from nitro/app.
• Use request/response/error/close hooks for cross-cutting runtime behavior.
• Customize response headers in the response hook via res.headers.