Dependency Upgrade Validation

The upgrade is the easy part; proving the project still coheres is the work. This skill takes over after versions are chosen -- typically bun update -i -r or an equivalent interactive pick -- and validates what landed: the real delta from git, peer and engine integrity, breaking changes and migrations across every version crossed, features worth adopting, and verification gates that run the project rather than reading about it. It also answers the inverse question: can a held-back package move, and why is it in package.json at all.

When to Use

• Validating a batch upgrade -- "I upgraded a lot of packages, validate everything"
• Assessing a held-back package -- "can we upgrade X?", "what blocks it?"
• Questioning a dependency -- "why do we even have X, we don't use it"
• Reading release notes -- breaking changes, migration steps, new features across the versions crossed
• Post-upgrade triage -- type, build or test failures that appeared after an update
• Pre-upgrade recon -- what a bump would cost before anyone runs it

Critical Rules

1. Detect the manager first, then use only its column. A Bun project gets bun throughout, a pnpm project pnpm, an npm project npm, a yarn project yarn. Another manager's CLI may not be installed at all, and if it is, it resolves against its own rules and can write a second lockfile or a differently-shaped tree. Every capability this skill needs has a native form in all four managers -- see the Capability Matrix -- so there is never a reason to reach across.
2. Establish the delta from git, never from the prompt. "I upgraded a lot of packages" is a starting point, not an inventory. The lockfile diff is the only complete record -- it carries transitive bumps that package.json never shows.
3. outdated reports drift, not compatibility. A clean bun outdated means every dependency sits at the newest version its range allows; it says nothing about whether the tree still resolves, builds or runs. Never report an upgrade as validated on that basis.
4. Peer ranges of ecosystem packages are the ceiling, not the registry's latest. A framework plugin pinning next@">=16.2.6 <17.0.0" caps the framework regardless of what the registry calls latest. Read the peers of the packages that wrap the target before proposing a bump.
5. A peer-required package is required with zero imports. graphql is a mandatory peerDependency of [email protected]; an app that never writes a query still must declare it. Run bun why and check every installed peer before proposing any removal (see references/dependency-audit.md).
6. Never run a migration, codemod, or version change without explicit approval. Report the exact command and what it will touch. Schema migrations additionally need an ordering and rollback story before they are worth proposing.
7. Read notes for every version crossed, not just the target. A breaking change introduced in 16.9 and unmentioned in 16.14's notes is still a breaking change for a project coming from 16.8.
8. Verify by running the project. Typecheck, build and tests are the evidence. A changelog that promises compatibility is not evidence.
9. Report what you did not check. Skipped packages, unread notes and untested paths belong in the report; silence reads as coverage.

Capability Matrix

Read down your project's column and use nothing else. Blank means the manager has no such command -- the workaround in the notes stays inside that manager.

Where the notes matter:

• Peer validation differs sharply in quality. pnpm peers check and yarn explain peer-requirements are purpose-built: both name the requiring package, the wanted range and the installed version, and pnpm peers check exits 1, so it works as a gate. npm has no dedicated command -- npm ls --all --json surfaces "invalid: <pkg>@<ver>" under .problems, and npm install --dry-run prints the full chain without writing. Bun has the weakest story (a non-fatal warning that names nobody), which is why it gets the script in references/dependency-audit.md.
• pnpm and yarn report peer problems during install, so the install output is worth reading rather than discarding: pnpm ends with Issues with peer dependencies found, yarn emits YN0060 naming the package and the six-letter p-prefixed hash that yarn explain peer-requirements takes.
• Only npm enumerates a version range directly. npm view '<pkg>@>16.8.0 <=17.0.2' version lists every match; bun info and pnpm view given the same range resolve to the single highest one instead, silently hiding what came between. Elsewhere, list all versions and filter.
• The yarn column is berry (v2+). Yarn Classic is a different CLI. Confirm which before running anything: yarn.lock with a .yarnrc.yml is berry, yarn.lock alone is v1. Classic keeps the npm-style surface -- yarn outdated, yarn info <pkg>, yarn audit --json, yarn why <pkg> (no --peers), yarn list, and yarn install --frozen-lockfile rather than --immutable. Running berry's yarn npm info or yarn dlx against v1 simply fails.
• Yarn berry has no outdated -- v1 does, and it was dropped in the rewrite, so yarn outdated on berry fails as an unknown script. On berry use yarn dlx taze or yarn upgrade-interactive.
• Bun's outdated has no JSON. --json is accepted and ignored. Parse the table -- the columns are Current | Update | Latest.

Filtering versions to a range, per manager:

# bun -- Bun.semver is built in, nothing to download
bun -e 'const vs = JSON.parse(await Bun.$`bun info graphql versions --json`.text());
  console.log(vs.filter(v => Bun.semver.satisfies(v, ">16.8.0 <=17.0.2"))
               .sort(Bun.semver.order).join("\n"));'

# npm -- native
npm view 'graphql@>16.8.0 <=17.0.2' version

# pnpm / yarn -- list, then filter with the semver CLI via that manager's runner
pnpm view graphql versions --json | jq -r '.[]' | xargs pnpm dlx semver -r '>16.8.0 <=17.0.2'
yarn npm info graphql -f versions --json | jq -r '.versions[]' | xargs yarn dlx semver -r '>16.8.0 <=17.0.2'

Semver ranges exclude prereleases unless the range names one, so canaries and rc builds drop out of all four without extra filtering.

Other tools are assumptions too. These recipes use jq and gh; neither ships with a package manager. Check before relying on them (command -v jq gh) -- gh additionally needs auth for release reads. Without jq, parse with the project's own runtime; without gh, fall back to WebFetch on the releases page.

Package Manager Detection

Check in this order -- the packageManager field wins where both exist, since it is what Corepack and CI enforce:

bun pm pkg get packageManager 2>/dev/null            # or: cat package.json | grep packageManager
ls bun.lock bun.lockb package-lock.json pnpm-lock.yaml yarn.lock 2>/dev/null
ls bunfig.toml .yarnrc.yml deno.lock 2>/dev/null     # bunfig.toml marks bun; .yarnrc.yml marks yarn berry

A deno.lock with no npm lockfile is a Deno project: none of the four columns apply, and the phases below still do (see references/package-managers.md). Say so rather than guessing a manager.

Workspaces change the shape of every command: a monorepo needs the recursive or filtered form, and every workspace package.json enters the delta.

Reference: See references/package-managers.md for the full verified per-manager command matrix.

Phase 0: Establish the Delta

Nothing else is trustworthy until this is exact.

# Declared changes (root + workspaces)
git diff HEAD -- package.json '**/package.json'

# Resolved changes, including transitive bumps nothing declared
git diff HEAD -- bun.lock            # or pnpm-lock.yaml / yarn.lock / package-lock.json

# Already committed on a branch
git diff origin/main...HEAD -- package.json '**/package.json' bun.lock

Classify every change, because the bump type sets how much scrutiny it earns:

Binary lockfiles produce no readable diff. For bun.lockb, either snapshot the resolved tree before and after with bun pm ls --all and diff the snapshots, or convert the project once to the text lockfile that has been the default since Bun 1.2:

cp bun.lockb /tmp/bun.lockb.bak                                      # keep the original
bun install --save-text-lockfile --frozen-lockfile --lockfile-only   # rewrites the lockfile only

--frozen-lockfile --lockfile-only keeps the conversion to a re-encoding: no resolution beyond what the lockfile already pins, and no touching node_modules. Without them the same command is free to resolve new versions, which changes the delta being measured.

The conversion leaves bun.lockb in place, and deleting it is the user's call, not a cleanup step -- it is the only copy of the resolution if the new bun.lock turns out wrong. Verify the converted file first (bun install --frozen-lockfile --dry-run succeeds against it, and the resolved versions match the pre-conversion bun pm ls --all snapshot), then ask before rm bun.lockb.

Confirm the working tree matches the lockfile before drawing any conclusion from it:

bun install --frozen-lockfile --dry-run          # bun   -- validates, writes nothing
npm ci --dry-run                                 # npm   -- validates, writes nothing
pnpm install --frozen-lockfile --lockfile-only   # pnpm  -- validates without linking
yarn install --immutable                         # yarn  -- validates, but installs

Bun and npm give a true dry run: both fail when package.json and the lockfile disagree, and neither touches disk. pnpm splits the job -- pnpm install --dry-run previews what an install would change while writing nothing, while --frozen-lockfile is the validation and installs as a side effect; pairing it with --lockfile-only checks without linking node_modules. Yarn has no dry run here: yarn install --immutable fails fast on drift and installs while doing it, so run it only where installing is acceptable.

Phase 1: Static Integrity

Run these before reading a single release note -- they are cheap and they catch the failures that no changelog would have warned about.

Peer conflicts (the highest-yield check). Use your manager's:

pnpm peers check                     # names package, wanted range, installed version; exits 1
yarn explain peer-requirements <hash>  # hash comes from the YN0060 line in install output
npm ls --all --json | jq '.problems'   # "invalid: <pkg>@<ver>"; npm install --dry-run for the full chain
bun run peer-check.ts                  # see references/dependency-audit.md

Bun is the one that needs the script. It reports a violated range as warn: incorrect peer dependency "[email protected]" -- non-fatal, naming nobody, and absent from any machine-readable output:

$ bun run peer-check.ts
CONFLICT [email protected] needs graphql@^0.9.0 || ... || ^16.0.0 -- installed 17.0.2

npm's plain npm ls is equally misleading -- at depth 0 it prints a peer-invalid tree as clean at exit 0, so --all --json is required.

Engines vs the runtime actually in use:

bun info <pkg>@<ver> engines     # npm view / pnpm view / yarn npm info -f engines
bun --version; node --version

Deprecations introduced by the bump:

bun info <pkg>@<ver> deprecated || echo "not deprecated"

A package that is not deprecated has no such property, and bun info treats a missing property as an error: error: Property deprecated not found, exit 1. That is the healthy case -- do not report it as a lookup failure. npm view and pnpm view print nothing and exit 0 for the same case.

Duplicate majors in the tree -- two copies of a stateful library (React, GraphQL, an ORM client) is a runtime bug, not a size problem. Use the Why-installed and Installed-tree rows of the matrix:

bun why <pkg> --depth 3          # pnpm why / npm why / yarn why --peers
bun pm ls --all                  # pnpm list --depth Infinity / npm ls --all / yarn info -A -R

Security posture after the bump:

bun audit --json | jq 'to_entries[] | {pkg: .key, advisories: [.value[] | {severity, title, vulnerable_versions}]}'
bun pm scan                      # bun only: lockfile scan, no installed tree needed

npm audit --json, pnpm audit --json and yarn npm audit --json answer the same question with their own output shapes -- read the shape before writing a filter.

Type package alignment -- @types/* majors track their runtime package's major. A mismatch surfaces as type errors during Phase 6, not as an install failure, so pair them in the delta table.

Reference: See references/dependency-audit.md for the peer-ceiling method, duplicate-major diagnosis, and the removal decision tree.

Phase 2: Release Notes

Budget this phase by the risk column from Phase 0. Fetching notes for every transitive patch burns context and buries the findings that matter.

bun info <pkg> repository        # npm view <pkg> repository.url / pnpm view / yarn npm info -f repository
bun info <pkg> homepage          # docs site, where upgrade guides live
gh release view v17.0.0 --repo <owner>/<repo> --json tagName,publishedAt,body

Enumerate every version crossed with your manager's row in the Capability Matrix. Only npm takes a range directly; with bun and pnpm, <pkg>@<range> resolves to the single highest match (bun info 'graphql@16' version returns 16.14.2), silently hiding everything in between.

Source order, cheapest first: node_modules/<pkg>/CHANGELOG.md (free, already on disk, but many packages ship none) -> gh release view -> the repo's CHANGELOG.md / UPGRADING.md / MIGRATION.md -> the docs site upgrade guide via WebFetch.

Extract only four things: breaking changes, migration steps, deprecations with their removal version, and additions that could replace code the project already hand-rolls. Everything else is noise.

Reference: See references/release-notes.md for repo resolution, the tag-naming fallback ladder, monorepo handling, and gh recipes.

Phase 3: Migrations

Release notes bury migration requirements in prose, and the two kinds fail differently:

• Code migrations -- codemods, renamed APIs, moved or reshaped config. Failure is loud and local: the build breaks.
• Schema and data migrations -- ORM or CMS model changes needing a generated migration committed and applied in a specific order relative to the deploy. Failure is silent in development and destructive in production.

Both get reported with exact commands, a required-now or optional verdict, and for schema migrations an ordering and rollback note. Neither runs without approval.

Reference: See references/migrations.md for detection patterns, per-ecosystem commands, and deploy ordering.

Phase 4: Held-Back and Suspect Packages

For each package the user did not upgrade, or suspects is unnecessary, answer both questions explicitly:

1. Why is it here? Direct and imported / direct because a peer requires it / transitive only and wrongly declared / genuinely unused.
2. What blocks the upgrade? Name the package and the peer range that caps it, or state that nothing does and the bump is available.

Never answer the first question from an import grep alone -- that is exactly how a required peer dependency gets deleted.

Reference: See references/dependency-audit.md for the full decision tree.

Phase 5: Adoptable Features

From the notes gathered in Phase 2, surface additions the project could use, ranked by what they delete: features replacing a hand-rolled workaround first, then those removing a dependency, then performance and DX. Check the project actually contains the pattern being replaced before suggesting it -- grep for the old API. These are proposals with an effort estimate, never edits.

Phase 6: Verification Gates

Cheapest first, stopping at the first failure and attributing it before moving on:

bun install --frozen-lockfile     # npm ci / pnpm install --frozen-lockfile / yarn install --immutable
bun run typecheck                 # or: bunx tsc --noEmit
bun run lint
bun run build
bun test                          # or the project's own test script

Substitute your manager's runner throughout (npm run, pnpm, yarn). Note that bun test is Bun's own runner: in a project whose tests are Jest or Vitest, the gate is bun run test, which executes the project's script. Read the actual script names from package.json rather than assuming; skip gates the project does not define and say so. Then a runtime smoke check -- boot the dev server, hit one route or entry point that exercises the upgraded packages. Type-clean and build-clean code still fails at runtime on changed initialization, config schemas and adapter APIs.

Map every failure to the package that caused it. "Build fails" is not a finding; "build fails because the config option was renamed in 16.0" is.

Phase 7: Report

Lead with the table, then the sections that need a decision:

| Package | Old -> New | Bump | Risk | Breaking | Migration | Action |
|---------|-----------|------|------|----------|-----------|--------|
| next    | 15.4.2 -> 16.3.1 | major | high | yes | codemod | run codemod |
| graphql | 16.8.0 (held) | -- | -- | -- | -- | blocked by payload peer ^16.8.1 |

Then, only where non-empty: Blocked (what caps each held package), Action required (migrations and code changes, with commands), Adopt (optional features with effort), Remove (dependencies proven unnecessary, with the evidence), Security (advisories resolved or introduced), Not checked (skipped packages and untested paths).

Commit the result by what changed, never by the process that produced it -- fix: update config for renamed option, not fix: post-upgrade fixes (see the git-commit skill).

Key Gotchas

1. A manager you did not detect may not be installed -- and if it is, it resolves by its own rules and can leave a second lockfile behind. npm in particular is not present on every machine that has bun. Every capability has a native form in all four managers (Capability Matrix); reaching across is never necessary and rarely harmless. The same caution covers jq and gh, which no manager installs.
2. bun outdated has no JSON output (through 1.3.x) -- --json is silently ignored and the table prints anyway. Parse the table (Current | Update | Latest) rather than switching managers for it.
3. bun info fails outside a project -- error: Bun could not find a package.json file to install from, including for plain registry lookups. Inside a project it is the right tool.
4. bun info <pkg> deprecated errors when the package is healthy -- error: Property deprecated not found, exit 1. A missing property is an error to bun info, so the good outcome looks like a failed command. Branch on the message, not the exit status (npm view prints nothing and exits 0).
5. bun info '<pkg>@<range>' version returns one version, not the range -- it resolves to the highest match, silently hiding every version in between. Enumerate with bun info <pkg> versions plus a Bun.semver.satisfies filter.
6. Bun.Glob brace alternatives cannot contain / -- {,@}/package.json matches fine, but {,@/*}/package.json matches nothing and reports no error, so a scan over nodemodules silently returns zero packages and every check built on it reports success. Use one pattern per shape. The same silent-zero applies to dot directories: nodemodules/.bun and node_modules/.pnpm are invisible to scan unless you pass dot: true.
7. Peer-conflict reporting is where the managers differ most -- pnpm peers check names package, range and installed version and exits 1; yarn prints YN0060 at install with a hash for yarn explain peer-requirements; npm needs npm ls --all --json -> .problems or npm install --dry-run; bun emits a non-fatal warning naming nobody. Do not assume the quality of one carries to another.
8. npm ls at depth 0 hides peer invalidity -- a tree with a violated peer range printed clean at exit 0. Use npm ls --all --json | jq '.problems'. In npm projects only: npm install --dry-run writes nothing (verified -- no package-lock.json appears) and prints the full requiring chain.
9. bun writes its banner to stderr and data to stdout -- bun audit --json | jq pipes cleanly; no stripping needed.
10. dist-tags can be polluted -- some packages carry dozens of canary and experimental tags. Read dist-tags.latest, never the first entry.
11. Release tag naming is inconsistent -- v17.0.2, 17.0.2, @scope/[email protected] in package-tagged monorepos, and release names that carry more than the version (React names tag v19.2.8 as 19.2.8 (July 21st, 2026), so name matching fails where tagName matching works). Resolve by ladder, do not guess once and give up.
12. Canary-heavy repos drown the release list -- gh release list --repo vercel/next.js returns mostly prereleases; pass --exclude-pre-releases.
13. repository.url can point at a renamed org -- React's metadata says github.com/react/react. gh follows the redirect, so pass it through rather than validating it by hand.
14. Many packages ship no changelog anywhere -- not in the tarball, not at the monorepo root. GitHub releases are then the only source, and for a few packages the docs site is.
15. Yarn berry has no outdated command -- it was not carried over from v1, and yarn outdated fails as an unknown script rather than an unknown command. Use yarn dlx taze or yarn upgrade-interactive.
16. Transitive bumps never appear in package.json -- a supply-chain incident or a breaking change in a nested dependency is visible only in the lockfile diff.
17. A same-day publish deserves a second look -- bun info <pkg> time --json dates every version. Every manager now ships a cooldown for this reason (bun install --minimum-release-age=<seconds>, npm install --min-release-age=<days>, pnpm's minimumReleaseAge setting, yarn's default time gate), so a version the tool refuses to pick may be held back deliberately, not broken.
18. knip and similar unused-dependency tools flag peer-required packages as unused -- that is the exact trap Critical Rule 4 exists for. Treat their output as a list of candidates to investigate, never as a removal list.
19. Lockfile drift outlives the upgrade -- widening a range without changing the installed version means the next clean install resolves differently. Flag range-only edits even though nothing appears to have changed.

Reference: See references/package-managers.md for the per-manager command matrix
Reference: See references/release-notes.md for release-note and changelog retrieval
Reference: See references/migrations.md for codemods and schema migrations
Reference: See references/dependency-audit.md for peer ceilings and dependency justification
Reference: See references/allowlist.md for auto-approval patterns