Large `__NEXT_PRIVATE_STANDALONE_CONFIG` causes `Error: spawn E2BIG`

[hdodov]

Link to the code that reproduces this issue

https://github.com/hdodov/test-nextjs/tree/bug-env-too-large

To Reproduce

1. Import a large JSON file in your next.config.js (e.g. to use as redirects)

2. Add some code that has to spawn a child process with the child_process module

3. Run Next with output: "standalone" and in prod mode

4. Run the app so that it runs the child process code

5. You'll see this error:

    ⨯ Error: spawn E2BIG
       at d (.next/server/app/page.js:1:2287)
       at l (.next/server/app/page.js:1:2358) {
     errno: -7,
     code: 'E2BIG',
     syscall: 'spawn',
     digest: '1763947400'
   }
   

When logging process.env, you can see that basically the entire JSON file is put in an environment variable:

That's what causes the E2BIG error, which happens when a process is spawned with either too long arguments or a too large set of environment variables.

Current vs. Expected behavior

Currently, you get a warning in dev mode, if you have too many redirects:

$ pnpm dev                            

> test-nextjs@0.1.0 dev /Users/hristiyan.dodov/Projects/test-nextjs
> next dev

   ▲ Next.js 15.3.3
   - Local:        http://localhost:3000
   - Network:      http://192.168.1.129:3000

 ✓ Starting...
Warning: total number of custom routes exceeds 1000, this can reduce performance. Route counts:
headers: 0
rewrites: 0
redirects: 2500
See more info: https://nextjs.org/docs/messages/max-custom-routes-reached
 ✓ Ready in 2.5s

What I'm expecting is to also see a warning that an environment variable will hold ALL OF THEM as JSON.

For my case, the performance impact was negligible and it wasn't a problem. But the fact that we had ~0.5MB in environment variables surely was.

Provide environment information

Operating System:
  Platform: darwin
  Arch: x64
  Version: Darwin Kernel Version 23.6.0: Thu Apr 24 20:26:36 PDT 2025; root:xnu-10063.141.1.705.2~1/RELEASE_X86_64
  Available memory (MB): 32768
  Available CPU cores: 16
Binaries:
  Node: 20.17.0
  npm: 10.8.2
  Yarn: N/A
  pnpm: 10.4.1
Relevant Packages:
  next: 15.3.3 // Latest available version is detected (15.3.3).
  eslint-config-next: 15.3.3
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: standalone

Which area(s) are affected? (Select all that apply)

Output

Which stage(s) are affected? (Select all that apply)

next start (local)

Additional context

No response

_NEXT-4662