npm ERR! ERESOLVE Could Not Resolve Dependency Tree

1. Why npm 7+ suddenly started blocking installs

Before npm 7, peer dependency mismatches were just a console warning — the install continued anyway. npm 7 changed two things at once: it started auto-installing peer dependencies (so you no longer had to npm install them yourself), and it started treating an unresolvable peer conflict as a hard error instead of a warning. That is why a package.json that installed fine on npm 6 now fails on npm 7–10.

npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: [email protected]
npm ERR! Found: [email protected]
npm ERR! node_modules/react
npm ERR!   react@"^18.2.0" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer react@"^16.8.0 || ^17.0.0" from [email protected]
npm ERR! node_modules/react-beautiful-dnd
npm ERR!   react-beautiful-dnd@"^13.1.1" from the root project

2. Read the tree to find the actual conflict

The error above always has two halves. Found: tells you what version is currently in your tree and why it's there. Could not resolve dependency: peer X from Y tells you which package (Y) declares a peer range that the found version does not satisfy. In the example above: your root project wants React 18, but [email protected] only accepts React 16 or 17 as a peer. Those two lines are the entire diagnosis — skip straight to them, ignore the rest of the tree noise.

• Common real-world pair: React 18 vs a UI library still pinned to a React 17 peer range (react-beautiful-dnd, older react-select, older framer-motion).
• Another common pair: ESLint 9 vs a plugin whose peerDependencies still says "eslint": "^8.0.0" because the plugin has not shipped a flat-config / ESLint 9 compatible release yet.

3. The correct fix: upgrade or override, not flags

Option A — upgrade the conflicting package. Check whether a newer major version already supports your peer's range:

npm view react-beautiful-dnd peerDependencies
npm view react-beautiful-dnd versions --json

# If a compatible major exists:
npm install react-beautiful-dnd@latest

Option B — npm overrides. If the package is abandoned or you can't upgrade yet, but you've verified it actually works with the newer peer at runtime, force the version in package.json:

{
  "name": "my-app",
  "overrides": {
    "react-beautiful-dnd": {
      "react": "$react",
      "react-dom": "$react-dom"
    }
  }
}

The $react syntax reuses whatever version is already at the root, so it stays in sync automatically. For pnpm, the equivalent lives under pnpm.overrides instead:

{
  "pnpm": {
    "overrides": {
      "react-beautiful-dnd>react": "$react"
    }
  }
}

After editing overrides, delete the lockfile and node_modules and reinstall clean — overrides only apply cleanly against a fresh resolution:

rm -rf node_modules package-lock.json
npm install

4. The escape hatches: --legacy-peer-deps vs --force

Both flags get you unblocked; neither one fixes the underlying mismatch. Use them to keep moving, then come back and apply option A or B above.

# Skips peer dependency checking entirely (npm 6 behavior)
npm install --legacy-peer-deps

# Checks peers, reports the conflict, installs anyway;
# also re-fetches and overwrites cached packages
npm install --force

5. npm vs yarn vs pnpm strictness

The three package managers disagree on how strictly to enforce peer ranges, because they structure node_modules differently:

• pnpm (strictest): non-flat, symlinked structure with no hoisting by default. A peer dependency must genuinely resolve within the dependent's own graph, so mismatches are impossible to hide. pnpm also warns on unmet peers by default even when the install technically succeeds.
• npm 7+ (strict, blocking): flat hoisted tree, but ERESOLVE hard-fails on unresolvable conflicts unless you pass --legacy-peer-deps or --force.
• yarn classic / yarn berry (looser): yarn classic only warns on peer mismatches, similar to old npm 6 behavior. Yarn Berry with PnP is stricter again, closer to pnpm, but plug'n'play mode is opt-in.