npm errornpm: “ERESOLVE unable to resolve dependency tree”

Which packages disagree, and the fix

1. 01

   A package with an outdated peer range

   The usual case: you upgraded React, Next.js, ESLint or TypeScript, and a plugin still declares a peer range for the old major version. Check whether a newer version of that plugin exists, and upgrade it.

   npm view some-package peerDependencies
   npm install some-package@latest

2. 02

   No compatible release yet: overrides

   “Overrides provide a way to replace a package in your dependency tree with another version, or another package entirely.” npm Docs, package.json: overrides

   If the plugin works with your version but has not updated its range, override the peer for that package in the root package.json, then run a clean install and test. The "$react" value reuses the react version your root package.json already declares, so react must be listed there.

   {
     "overrides": {
       "some-package": {
         "react": "$react"
       }
     }
   }

3. 03

   --legacy-peer-deps, and why it is a last resort

   “Use of legacy-peer-deps is not recommended, as it will not enforce the peerDependencies contract that meta-dependencies may rely on.” npm Docs, npm config: legacy-peer-deps

   It makes npm behave like npm 6 and skip peer dependencies entirely, so the install succeeds even when versions really are incompatible. If you use it, put it in .npmrc so every machine and CI install the same tree, and plan to remove it.

   # .npmrc
   legacy-peer-deps=true

4. 04

   It works locally but fails in CI or on Vercel

   A local node_modules or an .npmrc on your machine can hide the conflict. Delete node_modules, run npm ci (which installs exactly what the lockfile says), and commit the lockfile and any .npmrc the project needs.

Checked against the vendor’s docs on November 8, 2026: npm Docs: config (legacy-peer-deps); npm Docs: package.json (overrides).

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Related: Vercel “npm run build exited with 1” · npm and pnpm “ELIFECYCLE” · npm “EACCES: permission denied”