How to Receive Plaid Webhooks in Next.js

App Router Route Handler with raw body access

Next.js is the most-deployed full-stack JavaScript framework in 2026. The App Router's Route Handlers are a natural fit for webhook endpoints, but the default body parsing strips the raw bytes you need for HMAC verification — you have to read the request stream yourself. This guide walks through the Next.js setup for Plaid webhooks end to end: capturing the raw body, verifying the signature, handling retries idempotently, and iterating locally without redeploying. Cross-reference the Plaid Webhooks overview for the event catalog and sample payload.

1. Set Up the Next.js Endpoint

The endpoint needs to do three things, in this order: read the raw body, verify the signature against those exact bytes, and only then parse the JSON for your business logic.

// app/api/webhooks/[service]/route.ts
import { NextRequest } from "next/server";

export const runtime = "nodejs"; // signature verification needs Node, not Edge
export const dynamic = "force-dynamic"; // always run, never cache

export async function POST(req: NextRequest) {
  // IMPORTANT: read the raw body BEFORE you parse JSON.
  // HMAC verification has to run against the bytes the sender signed.
  const rawBody = await req.text();
  const signature = req.headers.get("x-signature-header") ?? "";

  // 1. Verify the signature against the raw body
  // 2. Parse JSON only after verification passes
  // 3. Process the event idempotently (use the event id as your key)

  const event = JSON.parse(rawBody);
  console.log("Verified webhook:", event.type ?? event);

  return new Response("ok", { status: 200 });
}

2. Verify the Plaid Signature

Node.js verification

// npm i jsonwebtoken jwk-to-pem
import jwt from 'jsonwebtoken';
import jwkToPem from 'jwk-to-pem';
import crypto from 'node:crypto';
import express from 'express';
import { PlaidApi } from 'plaid';

const plaidClient = new PlaidApi(/* ... */);
const app = express();

app.post(
  '/webhooks/plaid',
  express.raw({ type: 'application/json' }),
  async (req, res) => {
    const token = req.headers['plaid-verification'] as string | undefined;
    if (!token) return res.status(401).send('missing token');

    // Inspect JWT header to get kid.
    const [headerB64] = token.split('.');
    const header = JSON.parse(Buffer.from(headerB64, 'base64').toString());
    if (header.alg !== 'ES256') return res.status(401).send('wrong alg');

    // Fetch JWK from Plaid using the kid.
    const { data } = await plaidClient.webhookVerificationKeyGet({ key_id: header.kid });
    const pem = jwkToPem(data.key as jwkToPem.JWK);

    // Verify the JWT signature + iat freshness (5 min tolerance).
    const decoded = jwt.verify(token, pem, {
      algorithms: ['ES256'],
      maxAge: '5m',
    }) as { request_body_sha256: string };

    // Check the body hash matches what was signed.
    const bodyHash = crypto.createHash('sha256').update(req.body).digest('hex');
    if (
      bodyHash.length !== decoded.request_body_sha256.length ||
      !crypto.timingSafeEqual(
        Buffer.from(bodyHash),
        Buffer.from(decoded.request_body_sha256),
      )
    ) {
      return res.status(403).send('body hash mismatch');
    }
    res.json({ ok: true });
  },
);

Wire this verification call into the Next.js handler from section 1. The pattern is identical across Next.js versions: read raw body, verify, parse JSON, dispatch.

See Plaid's official signing docs for the canonical reference, or the cross-service signature verification guide for the same pattern in Ruby and other languages.

3. Make the Handler Idempotent

Plaid can — and will — send the same event twice. Network blips, your server returning a 5xx mid-processing, deploy windows: any of these triggers a retry, and your handler will see the same event id again. Build for that on day one rather than chasing duplicate-charge bugs in production.

The simplest pattern is a unique constraint on the event id in your database. The handler does the work inside a transaction, and the insert into the events table is the last step — if a retry arrives, the unique-constraint violation tells you the event already committed and you can return 200 without re-running the side effects.

4. Test Locally Without Deploying

The fastest iteration loop for any webhook handler is: capture a real Plaid event with HookRay, then replay that captured request against your local Next.js server until the verification + business logic both pass. No need to retrigger the event in Plaid, no need to redeploy.

1. Get a free webhook URL at hookray.com — no signup.
2. Paste the URL into your Plaiddashboard's webhook settings.
3. Trigger a test event. HookRay shows the headers, raw body, and parsed payload in real time.
4. Use HookRay's replay feature to send the captured request against http://localhost:3000/api/webhooks/plaid (or wherever your Next.js app is listening) — iterate on your code without re-poking the Plaid dashboard.

Deploying the Next.js Handler

Vercel runs Route Handlers on either the Node.js or Edge runtime. Pin runtime = "nodejs" for any handler that does HMAC verification — Edge's Web Crypto subset has surprising gaps for older signing schemes.

Need a host that boots quickly enough to absorb webhook bursts? DigitalOcean droplets stay warm, support raw-body proxies cleanly, and avoid the cold-start traps of some serverless runtimes.