Why does .next/cache not work after duplicating a Next.js project?

[ksnd0297]

Summary

I executed next build in my project and then copied the project.
When I run next build again in the copied project, the .next/cache doesn’t seem to work.

In the original project:

First build time: 26s

Second build time: 22s

In the copied project:

First build time: 26s

Why isn’t it 22s in the copied project?

Additional information

project : yarn create next-app@latest my-app --yes

Example

No response

[icyJoseph]

I hadn't look at this before, but I was inspecting the .pack files in the .next/cache/webpack folder, and I see some absolute paths - I am no expert on what's going on there, but I reckon the cache misses can be explained with that? You move to a different folder, and so it misses its cache?

[CoderDeltaLAN]

Context

• Next.js 14/15
• You ran next build, copied the project to a new folder, and built again
• Expectation: second build should be faster due to .next/cache

Why the cache didn’t help
The build cache is path- and environment-bound. When you duplicate a project:

• The absolute project path changes → cache keys no longer match.
• Tooling fingerprints include Node version, OS, compiler binary (SWC/Turbopack), and sometimes env vars.
• .next/cache is considered an ephemeral artifact, not portable across machines or root paths. Copying it does not guarantee reuse.

What to do instead

1. Don’t rely on copied caches. Treat .next/ as build output that can be deleted at any time.
2. For faster incremental builds, keep the same project path and environment between builds.
3. Ensure stable toolchain:
   • Same Node major (prefer Node 20 LTS)
   • Same Next.js version and lockfile (npm ci / pnpm i --frozen-lockfile / yarn --frozen-lockfile)
4. If you need repeatable fast builds in CI:
   • Cache your package manager cache (npm/pnpm/yarn), not .next/
   • Build inside the same runner path when possible
5. Local dev performance:
   • Use Turbopack in dev (next dev --turbo) for faster HMR
   • For production, expect a full compile on a new path even if .next/cache exists

Notes

• .next/ contents are not meant to be checked in or moved across paths; they’re invalidated when fingerprints don’t match.
• Official build docs: https://nextjs.org/docs/app/api-reference/next-cli#build

If this clarifies the behavior, please Mark as answer so others can find it.

[icyJoseph]

Hi, please try to keep the spam to a minimum. Most people have already asked an LLM before coming here.

It is more helpful if you process the information with your own take, rather than just pasting it here. Many people do that and often ends up being the right answer OP needed.

You have even commented a PR with totally unrelated content, asking to mark the PR as answered, which makes me think this has been done automatically, borderline spamming.