Migrating from Yarn guide

lpm migrate converts a Yarn project to LPM in one command. It detects yarn.lock, parses the lockfile, writes lpm.lock plus lpm.lockb when the graph fits the binary format, optionally configures .npmrc, runs lpm install, and verifies build + test when those scripts exist.

This guide covers the Yarn-specific parts. For the full flag reference, see lpm migrate.

Prerequisites

LPM installed - see Installation.
A package.json and yarn.lock in the project root.
A clean or committed working tree.

The current Yarn import path is built around Yarn Classic lockfile entries. Run the dry-run first and treat it as the source of truth for what will convert.

1. Preview

lpm migrate --dry-run

Dry-run detects Yarn, parses yarn.lock, converts the graph in memory, and writes nothing. It reports package counts, workspace counts, and any conversion problems before touching disk.

If the project contains multiple lockfiles, LPM chooses the most recently modified one. On timestamp ties, the priority order is bun.lockb, bun.lock, pnpm-lock.yaml, yarn.lock, then package-lock.json. Remove stale lockfiles before migrating so yarn.lock is the unambiguous source.

2. Run The Migration

lpm migrate

What runs:

Confirm package.json exists and refuse to overwrite an existing lpm.lock unless --force is set.
Parse Yarn lockfile entries: specifiers, exact versions, resolved tarball URLs, integrity strings, and dependency edges.
Mark direct dev and optional dependencies from root package.json, because Yarn Classic does not encode those flags per lockfile entry.
Write lpm.lock and, when supported, lpm.lockb.
Back up yarn.lock, .npmrc when touched, .gitattributes, and any pre-existing LPM lockfiles.
Add LPM registry routing to .npmrc unless --no-npmrc is set.
Run lpm install against the converted lockfile unless --no-install is set.
Run build + test scripts unless --skip-verify is set.

The flow is non-interactive. -y is accepted but reserved for a future interactive mode; it does not imply --force.

3. Verify

lpm install --offline
lpm test
lpm lint

lpm install --offline confirms the new lockfile and the warmed store can replay without network access. If your project does not have test or lint scripts, run the equivalent checks you normally trust before a package-manager migration.

4. Commit

git add lpm.lock .npmrc package.json
test ! -f lpm.lockb || git add lpm.lockb
git rm yarn.lock yarn.lock.backup .npmrc.backup
git commit -m "Migrate to LPM"

Do not commit .backup files unless you intentionally keep migration rollback artifacts in the repository.

Yarn-Specific Notes

yarn.lock resolved URLs from registry.yarnpkg.com are normalized into registry package entries when possible.
dependencies and optionalDependencies blocks inside lockfile entries both contribute dependency edges.
The install step rebuilds node_modules. Single-package projects default to LPM's hoisted v2 layout; workspaces and peer-conflict installs use isolated layout unless you override the linker.
Dependency lifecycle scripts remain denied by default. After migration, run lpm rebuild and lpm approve-scripts for packages that need install-time builds.

Rollback

lpm migrate --rollback

Restores backups from the previous migration run and removes LPM files created by that run. Safe to run repeatedly.

Migrating from Yarn