next-cache-components-adoption

# next-cache-components-adoption Enable Cache Components on an app and walk it to a passing build. This skill sequences the work; per-error recipes live in the dev overlay fix cards and the build's terminal output. The [migrating to Cache Components guide](https://nextjs.org/docs/app/guides/migrating-to-cache-components) is the canonical reference for the concepts and per-API recipes this skill applies — consult it whenever the skill steps reference a pattern (`"use cache"`, `cacheLife`, `<Suspense>` placement, etc.) and you want the full explanation. ## requires - **App Router project.** Cache Components is an App Router feature; `cacheComponents: true` does nothing for `pages/` routes. If the project has a `pages/` or `src/pages/` tree but no `app/` or `src/app/` tree, stop and tell the user — Pages → App migration is its own project, not part of this skill. A hybrid app (both `pages/` and `app/`) is fine: the flag affects the `app/` routes; `pages/` routes are unaffected and don't need opt-outs. - **A resolved app directory.** Locate `next.config.{js,ts,mjs,cjs}` first: that's the project root, and an agent invoked from a subdirectory would otherwise test for `app/` against the wrong `cwd` and find nothing. Look for `app/` and `src/app/` under it, and treat every command and glob in this skill as relative to whichever one exists. If both exist, Next.js builds `app/` and never looks at `src/app/`, so its routes are shadowed and unbuilt — tell the user that and ask which tree to migrate instead of picking one. - **A runnable app.** The whole loop verifies against `next dev` and a browser, so the app has to boot. If it reads a database or required env at import (e.g. an `env.ts` that throws on a missing `DATABASE_URL`), confirm it actually starts — with the real environment, or local data you stand up — before step 1. Adoption can't be verified against an app that won't run. - **Next.js 16.3 or later.** That release is where the pieces this skill relies on land: top-level `cacheComponents`, `export const instant`, the dev-overlay instant-navigation validation warnings, and the `cache-components-instant-false` codemod. If `next --version` reports below 16.3, upgrade first: - `npx @next/codemod@latest upgrade latest` to apply the version-to-version codemods. - Read the relevant [version upgrade guide](https://nextjs.org/docs/app/guides/upgrading) (e.g. [Version 16](https://nextjs.org/docs/app/guides/upgrading/version-16)) for what the codemod doesn't cover. - **No incompatible config keys.** `cacheComponents: true` errors on any file that still exports `dynamic`, `revalidate`, or `fetchCache`. **Translate, don't delete.** Each export encodes behavior the route needs to keep doing; migrate each one to its Cache Components equivalent via the [migration guide's per-key sections](https://nextjs.org/docs/app/guides/migrating-to-cache-components#enable-cache-components). The exception is `dynamic = 'force-dynamic'`: under Cache Components every route is already dynamic by default, so the migration guide removes it outright rather than translating it — don't overthink a batch of identical `force-dynamic` deletions. `revalidate` and `fetchCache` still need real translation. If a value can't be cleanly translated yet, leave a `// TODO: Cache Components adoption — restore revalidate = 3600` comment so the loop picks it up. The `cache-components-instant-false` codemod does not touch these. - **`experimental.dynamicIO` is fatal.** It was renamed to top-level `cacheComponents` and the old key now aborts before any build can run — remove it (or replace with `cacheComponents: true`) first. `experimental.useCache` is still accepted as a deprecated alias; redundant once `cacheComponents: true` is set, so remove it for clarity. ### notes - **No passing baseline before the flag.** If the app already uses `"use cache"`, the pre-flag build errors with `please enable the feature flag cacheComponents`. Enabling the flag is the first thing you do (in Incremental, before the codemod; in Direct, before fixing routes) — not a thing to do _after_ getting a passing build. Note this in your starting summary so it doesn't read as a regression. - **Offline docs.** Guide links have offline copies under `node_modules/next/dist/docs/` (bundled since Next.js 16.2), with the directory layout numbered for ordering (e.g. `node_modules/next/dist/docs/01-app/02-guides/migrating-to-cache-components.md`). If you can't predict the numbered prefix, `find node_modules/next/dist/docs -name '<slug>.md'` resolves it. The `/docs/messages/*` error pages are not bundled. - **Older versions without bundled docs.** Suggest `npx @next/codemod@latest agents-md` to the user before starting: it downloads a version-matched copy to `.next-docs/` and writes an index into `AGENTS.md` / `CLAUDE.md`. It touches files in their repo, so ask first and run it only if they want it. ## the shape of the work There's one loop: walk the route tree top-down, one feature at a time, adopting each route against `next dev` + a browser. The build is a final check for each feature, not the working surface. The choice in step 1 is whether to opt every route out of validation first or fix routes as you go. Either way the loop is the same: - **With a quiet pre-step (Incremental).** Run the codemod to opt every page and layout out of validation. Once you've also fixed what the codemod can't (sync-IO calls, leftover `revalidate`/`dynamic`/`fetchCache` exports), the build passes; you ship that as its own PR and then start the loop — removing one opt-out at a time and adopting that route. This splits the work into small, reviewable PRs. - **Without (Direct).** Enable `cacheComponents` and start the loop on whatever the build flags first. Same loop, but every fix sits on one branch until adoption is complete. In both, the per-route success bar is the same: **dev loop reports no errors AND `next build` passes**. Check in with the user after every feature, and suggest a commit but never make one without their confirmation. Expect to spend most of the time in the loop, not in the pre-step. ## background `cacheComponents: true` requires every route to be prerenderable. A route that reads request-time data outside `<Suspense>` is "blocking" and fails the build. `export const instant = false` marks a route as allowed to block, which clears it in both dev and build; on a layout it covers the whole subtree during the build, but client navigations still validate each descendant segment on its own. Reads wrapped in a [`"use cache"`](https://nextjs.org/docs/app/api-reference/directives/use-cache) function count as cache boundaries, not blocking reads. Three classes of blocker come up, usually in this order: 1. **Request-time reads** (`cookies()`, `headers()`, `await params`, `await searchParams`). All four block when awaited at the top of a page or layout. `params` and `searchParams` often get missed because they're not framed as "request data" the way cookies and headers are. The fix is to push the read into a `<Suspense>`-wrapped child — and for `params`/`searchParams`, forward the promise into the child and await it there; don't `await` at the page top. 2. **Sync-IO at module/render time** (`new Date()`, `Date.now()`, `Math.random()`, `crypto.randomUUID()`). These fail the build even with `instant = false` — the opt-out doesn't suppress them. If they're in a shared layout, they block every route under it. The codemod can't fix them; you have to translate each one by hand before the build can pass (see the [incremental pre-step](#incremental)). Grep the whole repo for these calls before running anything else. 3. **`"use cache"` files that read request data.** A file with a top-level `"use cache"` directive can't export `instant`; combining the two errors with `Only async functions are allowed to be exported in a "use cache" file.`, which means the directive was wrong for that route. Remove it before running the codemod. ## working surfaces ### finding blocking routes Prefer `next dev` over `next build` while you work. - **`next dev`** — the working surface. Visit a route; its blocking errors surface in the dev overlay with full stack traces and fix cards linking the per-error docs. Work one route at a time — errors don't accumulate in one place. The route itself still returns HTTP 200, so read the overlay (or `.next-dev.log`), not status codes. A cleared overlay is one half of calling a route clean — the other half is browser verification (see [step 2](#step-2-the-inner-loop-remove-opt-outs-one-feature-at-a-time)) and a passing build for that route. - **`next build`** — detection only. The build is `next dev`'s authoritative check, not its replacement. Use it as the last gate on each feature in the loop (a passing build is part of the per-route success bar) and as the final verification across the whole app. In Incremental, the build also confirms the pre-step (codemod opted every route out, no shared layout still has a sync-IO blocker) before you ship that PR. Don't reach for the build instead of the dev loop while you're working a route — a passing compile doesn't tell you what ended up in the static shell and what streamed. By default the build stops at the first blocking route, so it's also poor for sizing the work. Two flags help when iterating: `--debug-build-paths` builds only the routes you name (comma-separated glob patterns of file paths relative to the project root, e.g. `--debug-build-paths="app/admin/**/page.tsx"` — not URL paths; `--debug-build-paths="app/(marketing)/about/page.tsx"` — not `/about`; `--debug-build-paths="app/admin"` matches nothing and silently builds zero routes), and `--debug-prerender` disables the early exit so the build continues past the first prerender failure, reports every blocking route, and prints a fuller stack trace that names the originating file and line. Every blocking error has a docs page — open it. Both the dev overlay and the build terminal print a `https://nextjs.org/docs/messages/<slug>` link with each error. That page is the canonical recipe for the fix; the inline message is a summary. Fetch the link for every distinct error you encounter, even if you think you know the pattern — the recipes evolve, and the same error class can have different correct fixes depending on what the route reads. Don't improvise from the inline message alone. (`/docs/messages/*` pages aren't bundled offline; if you have no network, fall back to the per-API guides under `node_modules/next/dist/docs/` and note the limitation when you report back.) ### verifying each fix at runtime A passing build or a cleared overlay isn't proof the route actually behaves — Cache Components is a runtime concern (a static shell with streamed data). Verify after every fix, not only at the end. In preference order: 1. **[`next-dev-loop`](https://github.com/vercel/next.js/tree/canary/skills/next-dev-loop) — strongly preferred.** Cross-checks `/_next/mcp` against the live browser via `agent-browser` and surfaces both compile and runtime issues in one pass. The diagnostics (React tree, suspense boundaries, console + network) are richer than poking at `next dev` by hand. Install it before starting the loop. Don't wait until you hit something `next dev` alone can't explain. Run: ```bash npx skills add https://github.com/vercel/next.js/tree/canary/skills/next-dev-loop ``` The skill states its required `agent-browser` version and walks you through it. **Requires Turbopack.** If `package.json`'s `dev` script passes `--webpack`, flag it to the user and ask whether there's a reason to stay on webpack. If not, switch to Turbopack (the Next.js 16.3+ default). If they want to keep webpack, skip this install and use the [build-only loop](#the-loop-build-only-fallback) instead. You don't need permission to install `next-dev-loop` itself. It's a tool, like installing a dev dependency. If a user is present, briefly tell them you're installing it for verification. In a non-interactive run (CI, dashboard, sandbox), install it without asking — "can't prompt the user" is not a reason to skip. The only legitimate skip is a real technical blocker: no network, no npm, read-only filesystem, a stated no-new-deps policy, or a webpack-only dev script. If you skip, name the specific blocker in your final report. 2. **A browser you can drive yourself.** Playwright, `agent-browser` directly, any browser-automation tool. Use only when `next-dev-loop` is genuinely blocked. You'll miss the framework-side checks (`/_next/mcp`), so DOM assertions alone don't catch every regression — be more cautious about what you call "verified." 3. **Build-only.** If you can't run a dev server at all, the build is your only signal. `○ (Static)` routes with no `<Suspense>` are fully verified by the build (nothing streamed to test). `◐ (Partial Prerender)` routes are only shell-verified — flag them when you report back. 4. **No tooling at all.** Ask the user to run the dev server (or build) and report what they see, or hand off the milestone you've reached. ## step 1: choose a strategy Ask the user, in terms of the PRs they want, not the size of the job. Never use the internal labels (Incremental, Direct) when talking to the user — those are your own scaffolding. Ask in terms of PRs and features, e.g.: _"Do you want me to first open a PR that turns on Cache Components and opts every route out of validation, then handle the actual route adoptions feature-by-feature in follow-up PRs? Or do everything on one branch?"_ Even on a tiny app, the incremental path still has value (review-sized PR, revertible, the `// TODO: Cache Components adoption` markers double as your work queue for next session). Don't pick on their behalf. If there's no user to ask, default to **Incremental** and document the choice. - **Incremental** — quiet pre-step + the loop. Run the codemod to opt every page and layout out of validation, get the build passing, stop and check in with the user (see [end of the pre-step](#end-of-the-pre-step-check-in)), then enter [step 2's loop](#step-2-the-inner-loop-remove-opt-outs-one-feature-at-a-time) and ship each feature as a follow-up PR. - **Direct** — skip the pre-step. Enable `cacheComponents` and go straight to [step 2's loop](#step-2-the-inner-loop-remove-opt-outs-one-feature-at-a-time); the build's blocking routes are the work queue. ### incremental Before invoking the codemod, fix the two classes of blocker it can't. 1. **Sync-IO at module/render time.** Grep the whole repo for `new Date()`, `Date.now()`, `Math.random()`, and `crypto.randomUUID()` (not only `app/**/layout.{js,jsx,ts,tsx}` — the read might live in any component imported by a layout). Unblock each match with the `await connection()` + `<Suspense>` fix from its `blocking-prerender-*` error card: it defers the value to request time, exactly as it behaved before the migration, so it needs no product decision. Add this exact comment on the line above the `await connection()`: ```tsx // TODO: Cache Components adoption. Added to unblock the build: remove this connection() to re-trigger the error and review the fix options. ``` It shares the `TODO: Cache Components adoption` prefix with the comments the codemod writes, so the check-in grep finds both. Removing the `await connection()` makes the error fire again with its fix cards — the same motion as removing an opt-out in the loop. 2. **Incompatible segment configs.** Grep for `^export const (revalidate|dynamic|fetchCache)` across the app directory and translate per the `requires` note above. The codemod does not touch them; leaving them in place fails the build after the codemod. The codemod refuses to run on a dirty working tree. Commit or stash unrelated work first, or pass `--force` to let its edits land alongside your WIP. Common false positive: if you recently upgraded Next.js, `package.json` and the lockfile will already be dirty — commit those first. ```bash npx @next/codemod@latest cache-components-instant-false ./app ``` Pass the app directory you resolved in [requires](#requires). A wrong path is not an error: it reports `0 ok` and exits `0`, so read the file count and treat zero as a failed run, not an adopted app. Inserts `export const instant = false` (with a `// TODO: Cache Components adoption` comment) into every `{page,layout,default}` file under that directory, skipping files that already declare `instant` and any module marked `"use client"` or `"use server"`. Then set `cacheComponents: true`. The TODO comments are the work queue for the loop. If the codemod isn't available (older `@next/codemod`, sandboxed environment, offline run), reproduce it by hand: for every `{page,layout,default}.{js,jsx,ts,tsx}` in the app directory that isn't `"use client"` or `"use server"` and doesn't already declare `instant`, insert this after the imports: ```ts // TODO: Cache Components adoption. Refactor this route so this opt-out can be removed. // See: https://nextjs.org/docs/app/guides/migrating-to-cache-components export const instant = false; ``` The codemod opts every segment out, not only the root, on purpose. Resolution is top-down, first-explicit-config-wins: the highest `instant = false` decides the whole subtree. With an opt-out on every segment, removing one segment's opt-out validates only that segment; descendants keep their own opt-outs and stay passing. If only the root were opted out, removing it would re-arm validation for the entire app at once. Because the highest opt-out wins, remove them top-down (root layout first, then descend). Removing a leaf's opt-out does nothing while an ancestor still holds one. Confirm the pre-step with `next build`. The build is the proof, not the codemod run — a shared layout that calls `new Date()` / `Math.random()` directly still fails regardless of the opt-out (see [background](#background)). After the build passes, confirm the root layout got an opt-out (`grep -n "export const instant" <app dir>/layout.*`). The root layout renders every route, including framework routes like `/_not-found`, so if it was missed, add `export const instant = false` to it by hand. Synthetic routes like `/_not-found` have no user file — when they block, fix the root layout's opt-out, not the synthetic route. Client Components (`"use client"`) get no opt-out (it's a build error — `E1344` — to export `instant` from them), but they are not a rare blocker. The high-frequency case is a client component in the root layout's nav or header calling `usePathname()`/`useSearchParams()`: it blocks _every_ dynamic route with `blocking-prerender-client-hook`, and static routes pass (the pathname is known at prerender), which masks it until you reach a dynamic segment. It's not an ancestor-data fix — follow the [error's docs page](https://nextjs.org/docs/messages/blocking-prerender-client-hook) for the `<Suspense>` recipe. Only when a client route blocks on _server_ data do you fix that data in its ancestor. ### end of the pre-step: check in Incremental only. Stop here before starting step 2 — the pre-step is the shippable PR. Talk to the user in their language; don't say "Incremental" or other internal labels; talk about adoption, PRs, and what the app does now. Tell them: - What you did: turned on Cache Components, ran the codemod that opts every page and layout out of the new validation (or did it by hand), fixed any blockers the codemod can't (list them), confirmed the build passes. - What changed: every page and layout in the app directory now exports `instant = false` with a `// TODO: Cache Components adoption` comment, except client components and any that already had an `instant` export. - What to sanity-check: the diff is mostly mechanical (new exports + comments). The build passes. Routes still behave exactly as they did before — the opt-outs preserve current behavior; no rendering changes yet. - The question: "Want to open this as its own PR before we start adopting Cache Components route by route? Or keep going on this branch?" Wait for the answer. Moving to step 2 without checking in defeats the point of taking the incremental path. ### direct Set `cacheComponents: true` and move to [step 2](#step-2-the-inner-loop-remove-opt-outs-one-feature-at-a-time). The build's blocking routes are the work queue. ## step 2: the inner loop, remove opt-outs one feature at a time A "feature" is a single product surface — `app/settings/profile/**`, `app/posts/[slug]/**` — not a whole top-level app like `app/dashboard/**`. Finish one end-to-end before starting the next. Within a feature, walk top-down (layouts before pages, root layout first). Removing a layout's opt-out before its descendants exposes the layout's own blocking reads. (Direct: there are no opt-outs to remove — fix each failing route; if a hand-written opt-out on an ancestor shadows it, remove that first.) A passing build mid-walk doesn't mean the layout is clean. Removing a layout's opt-out while its descendant pages still have theirs keeps the build passing — each page shadows the inherited validation. The layout's actual blocking reads only surface once nothing below it shadows them. Don't call a feature done at the layout boundary. Use the **with-a-browser** loop unless a browser is genuinely unreachable. The [`next-dev-loop`](#verifying-each-fix-at-runtime) skill is the source of truth for what counts as "browser available" and how to install it.