npm ERR! code ERESOLVE: unable to resolve dependency tree

Published 2026-05-01

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Root Cause

This error occurs when npm (v7 and above) encounters conflicting peer dependencies. A package you are installing requires a specific version of a peer dependency (like React 17), but another package or your root project requires a different, incompatible version (like React 18). npm halts the installation to prevent unpredictable behavior that could arise from using an unsupported version combination.

Fix / Solution

The safest approach is to update the offending packages so their peer dependency requirements align. If that's not possible, you can use the `--legacy-peer-deps` flag to force npm to ignore peer dependency conflicts (reverting to npm v6 behavior), or `--force` to resolve all conflicts by installing the latest versions. Be cautious with these flags as they may cause runtime errors.

Code Snippet

# ❌ Fails due to peer dependency conflict
npm install some-legacy-package

# ✅ Bypasses the strict check (use with caution)
npm install some-legacy-package --legacy-peer-deps