Next.js Upgrade Protocol

Automated and manual migration steps for Next.js version upgrades (e.g., v14 to v15).

Priority: P1 (HIGH)

Workflow: Upgrade Next.js to New Major Version

1. Check current versions of next, react, react-dom in package.json
2. Plan incremental path (e.g., v13 -> v14 -> v15; never skip majors)
3. Run codemods: npx @next/codemod@latest <transform> <path>
4. Update dependencies: See implementation examples
5. Verify async APIs: ensure cookies(), headers(), params awaited (v15+)
6. Audit fetch caching: v15 defaults to no-store; add force-cache where needed
7. Run next build and fix hydration or Turbopack errors
8. Report codemod failures or manual fixes to team

Implementation Guidelines

• Upgrade Detection: Always check package.json for versions of next, react, and react-dom.
• Planning: For major version jumps (v13 to v15), perform incremental upgrade (v13 -> v14, then v14 -> v15). Follow official Next.js Migration Guides.
• Automated Codemods: Use npx @next/codemod@latest <transform> <path> to automate syntax migration.
• Breaking Changes (v15): Respond to next-async-request-api transform by ensuring params, searchParams, cookies(), and headers() awaited.
• React Parity: Upgrade react and react-dom to match Next.js peer dependencies (e.g., React 19 for Next.js 15).
• Validation: Run next dev and next build after each incremental step. Check console errors for hydration warnings.

Anti-Patterns

• No major version skipping: Upgrade one major version at time (13 -> 14, then 14 -> 15).
• No manual breaking-change fixes: Always run npx @next/codemod@latest transforms first.
• No assumed caching behavior post-upgrade: v15 defaults to no-store; audit all fetch calls.
• No async page functions in Pages Router: export default async function Page() fatal.

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• incremental
• one major