Function Duration

These rules catch patterns that inflate the wall-clock time of your serverless functions. Shorter functions mean lower bills — Vercel charges per GB-second of execution time.

async-parallel

Detects 3 or more sequential await statements that appear independent — meaning later awaits don't reference variables from earlier ones.

Why it matters: Sequential awaits run one after another. If they're independent, running them in parallel with Promise.all() can cut function duration significantly.

const users = await db.user.findMany();
const posts = await db.post.findMany();
const comments = await db.comment.findMany();

const [users, posts, comments] = await Promise.all([
  db.user.findMany(),
  db.post.findMany(),
  db.comment.findMany(),
]);

server-after-nonblocking

Detects console.log(), console.info(), console.warn(), analytics.track(), analytics.identify(), or analytics.page() calls in server actions (files with "use server").

Why it matters: Logging and analytics calls block the response until they complete. Wrapping them in after() lets the response finish immediately while the work continues in the background.

"use server";

export const updateUser = async (data: FormData) => {
  await db.user.update({ ... });
  console.log("User updated");
  analytics.track("user_updated");
};

"use server";

import { after } from "next/server";

export const updateUser = async (data: FormData) => {
  await db.user.update({ ... });
  after(() => {
    console.log("User updated");
    analytics.track("user_updated");
  });
};

vercel-edge-sequential-await

Detects edge runtime files with 2 or more sequential await calls without Promise.all.

Why it matters: Edge functions have strict execution time limits. Sequential I/O wastes precious milliseconds that could be parallelized.

export const runtime = "edge";

export async function GET() {
  const user = await getUser();
  const settings = await getSettings();
  return Response.json({ user, settings });
}

export const runtime = "edge";

export async function GET() {
  const [user, settings] = await Promise.all([getUser(), getSettings()]);
  return Response.json({ user, settings });
}