Fix · Node, npm and build

npm ERESOLVE: dependency conflict

What you may see

npm install stops with unable to resolve dependency tree
It tells me to use --force or --legacy-peer-deps

Most likely cause

Two packages need different versions of a third one, often after upgrading React or Next.

Check first (about two minutes)

Read the lines "Found:" and "Could not resolve dependency": they name the packages in conflict.

The fix prompt

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The exact error or what you see

What you did before it happened

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Prompt language

You are a patient senior engineer who knows Node.js, npm and build tools and explains them to people who are not developers. I am not a developer, so explain every step in plain words and tell me exactly which button, menu or command you mean. If you are not sure about something, say so; do not guess.

THE PROBLEM
npm ERESOLVE: dependency conflict

THE EXACT ERROR OR WHAT I SEE
[paste the exact error here]

WHAT I DID BEFORE IT HAPPENED
[write in a few words what you did before it happened]

MOST LIKELY CAUSE
Two packages need different versions of a third one, often after upgrading React or Next.

DO THESE STEPS, IN THIS ORDER
1. Show the conflict and which package asks for which version.
2. Look for the version of the old package that supports my version, or a newer package that does.
3. Only if there is no safe alternative, explain what --legacy-peer-deps means and ask me before using it.
4. Run npm install and then the build and a quick test.
Stop and tell me if what you see does not match a step. Do not skip ahead.

CHECK THAT IT WORKED
- npm install finishes and the app builds and runs.
Tell me exactly what I should see on the screen when it works.

DO NOT CHANGE
- Do not upgrade React, Next or other main packages to new major versions without telling me.
- Anything I did not ask about: the design, the text, other pages, other settings or the data.
- Do not delete files, data or branches, do not reset or force-push, and do not rewrite history, unless you first show me exactly what would be lost and I say yes.
- Do not paste, print or ask me to paste a password or secret key into this chat. If one is needed, tell me which settings page of the right service to store it in.

WHEN YOU FINISH
Explain in simple words what you changed (file by file or setting by setting), why you changed it, and how I can undo it.

Paste it into Claude, ChatGPT, Gemini or Cursor, then follow what it says.

After you tried it, did it work?

Steps

Show the conflict and which package asks for which version.
Look for the version of the old package that supports my version, or a newer package that does.
Only if there is no safe alternative, explain what --legacy-peer-deps means and ask me before using it.
Run npm install and then the build and a quick test.

Do not do this

Do not use --force as the first answer.
Do not upgrade React, Next or other main packages to new major versions without telling me.

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