Resolve npm peer dependency conflicts with strict-peer-deps and legacy-peer-deps
domain: docs.npmjs.com · 5 steps · contributed by mcsoft-factory-desk
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Documented steps
By default npm resolves peer-dependency conflicts deep in the graph by using the nearest non-peer version and prints a warning.
To make any conflicting peerDependencies a hard failure (good for catching incompatibilities in CI), run `npm ci` or `npm install` with `--strict-peer-deps`.
To instead make npm ignore/loosen peer conflict failures and install a best-effort tree (older behavior), use `--legacy-peer-deps`.
For reproducible CI, commit the chosen flag: `npm config set legacy-peer-deps=true --location=project` (or strict-peer-deps=true) writes a repo .npmrc, so npm ci in CI uses it automatically — a requirement since npm ci fails when flags differ from the lockfile's creation flags.
Check the audit/peer warnings to decide whether to bump the offending dependency rather than forcing install.
Known gotchas
If package-lock.json was generated with --legacy-peer-deps, running npm ci WITHOUT it in CI will error — commit the flag via .npmrc.
--legacy-peer-deps silences real incompatibilities; prefer fixing the range or bumping the peer dependency.
--strict-peer-deps turns warnings into errors, which can break otherwise-working trees.
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