experimental.middlewareClientMaxBodySize

When middleware is used, Next.js automatically clones the request body and buffers it in memory to enable multiple reads - both in middleware and the underlying route handler. To prevent excessive memory usage, this configuration option sets a size limit on the buffered body.

By default, the maximum body size is 10MB. If a request body exceeds this limit, the body will only be buffered up to the limit, and a warning will be logged indicating which route exceeded the limit.

Options

String format (recommended)

Specify the size using a human-readable string format:

import type { NextConfig } from 'next'   const nextConfig: NextConfig = {  experimental: {  middlewareClientMaxBodySize: '1mb',  }, }   export default nextConfig

Supported units: b, kb, mb, gb

Number format

Alternatively, specify the size in bytes as a number:

import type { NextConfig } from 'next'   const nextConfig: NextConfig = {  experimental: {  middlewareClientMaxBodySize: 1048576, // 1MB in bytes  }, }   export default nextConfig

Behavior

When a request body exceeds the configured limit:

1. Next.js will buffer only the first N bytes (up to the limit)
2. A warning will be logged to the console indicating the route that exceeded the limit
3. The request will continue processing normally, but only the partial body will be available
4. The request will not fail or return an error to the client

If your application needs to process the full request body, you should either:

• Increase the middlewareClientMaxBodySize limit
• Handle the partial body gracefully in your application logic

Example

import { NextRequest, NextResponse } from 'next/server'   export async function middleware(request: NextRequest) {  // Next.js automatically buffers the body with the configured size limit  // You can read the body in middleware...  const body = await request.text()    // If the body exceeded the limit, only partial data will be available  console.log('Body size:', body.length)    return NextResponse.next() }

import { NextRequest, NextResponse } from 'next/server'   export async function POST(request: NextRequest) {  // ...and the body is still available in your route handler  const body = await request.text()    console.log('Body in route handler:', body.length)    return NextResponse.json({ received: body.length }) }

Good to know

• This setting only applies when middleware is used in your application
• The default limit of 10MB is designed to balance memory usage and typical use cases
• The limit applies per-request, not globally across all concurrent requests
• For applications handling large file uploads, consider increasing the limit accordingly