--- name: next-cache-components-optimizer description: > Optimize the meaningful UI available immediately from a Next.js route on an initial load (hard navigation) or named client-side navigation (soft navigation). Encode the goal as a failing @next/playwright instant() e2e and work it to green, one verified route and entry point at a time; the shipped test then guards against regression. Use when asked to grow a static shell, fix a slow first paint or non-instant navigation, diagnose which Suspense boundary blocks useful UI, or add instant() regression coverage. Requires Next.js 16.3+ with Cache Components already adopted. --- # next-cache-components-optimizer Set up an agentic optimization loop that drives a Next.js route from "not instant" to "instant" and keeps it there. The loop is test-driven: encode the goal as a failing `@next/playwright` `instant()` test, work it to green, and ship the test as the regression guard. Run it once per target route and entry point. Work the phases P → G in order; each ends in a gate. Before changing the route, read the bundled **Optimizing the static shell** guide at `node_modules/next/dist/docs/01-app/02-guides/optimizing-the-static-shell.md`. If it is unavailable, use the [online guide](https://nextjs.org/docs/app/guides/optimizing-the-static-shell). The guide owns the framework behavior and implementation patterns. This skill owns the navigation contract, production rig, trustworthy RED-to-GREEN loop, parity check, differential, and report. ## What is invariant, and what is yours One thing here is fixed. The rest is yours. Read this before treating any command, platform, or env var below as a requirement. - **Invariant: the verification loop.** Maximizing the shell is worthless unless you can prove it. The proof is an automated check: under a lock that gates dynamic data, the static shell still commits. RED shows the gap, GREEN shows it closed, the test ships as the regression guard. It must run on a production-like build and must not be able to pass vacuously. Stand the loop up once; every later optimization is then verifiable by construction. The loop is the deliverable, not any one route. - **The mechanism: `@next/playwright` `instant()`.** This skill uses [`instant()`](https://nextjs.org/docs/app/guides/instant-navigation#prevent-regressions-with-e2e-tests) as a ruler, not a stopwatch (phase A). It comes from `@next/playwright` (installed alongside `@playwright/test`, on the same release line as `next`), so it isn't tied to any host. Keep it. Timing a navigation by hand is too flaky to trust, and is the failure mode this skill exists to prevent. - **Yours: the rig.** How you build, deploy, authenticate, configure Playwright, and loop belongs to your stack, not to this skill. A local `next build && next start`, a CI/staging container, and a per-push preview deploy are equally valid rigs; the verdict comes from the build, never the platform. Phase 0 maps the invariant onto your repo. Read every platform name, env-var spelling, and command below as an example to translate, not a requirement. ## Two entry points, two instant UI contracts A route reaches the user two ways: - **Initial load (hard navigation)** commits the route's prerendered static shell; deferred parts stream in behind their loading skeletons (Suspense fallbacks, `loading.tsx`). - **Client-side navigation (soft navigation)** reuses shared layouts and commits the available App Shell for the destination segments that change. The same implementation patterns can make either entry point instant. The test differs only in how the navigation is driven ("Driving the navigation in tests" below), and the available UI can differ because a soft navigation reuses layouts above the source and destination's divergence point. Guard the entry point the user named, and both when both matter. See [What "instant" means](https://nextjs.org/docs/app/guides/instant-navigation#what-instant-means). This skill is therefore not limited to increasing the direct-load static shell. It can also fix a non-instant client navigation when caching reusable work or moving request-time work behind a focused boundary makes the destination's available App Shell commit immediately. When that App Shell is already instant and the goal is to fetch additional URL-specific content before the click, hand off to `next-partial-prefetching-optimizer`. ## Goal Make the most meaningful available App Shell UI commit immediately, and let only genuinely request-time work stream afterward. The shipped test deterministically encodes **present ∧ instant**. **Non-blank** is the additional bar the workflow enforces by judgment because an `instant()` pass alone is satisfied by an empty shell. `instant()` is a ruler, not a stopwatch: assert that the shell appears under the lock; do not time it. A trustworthy verdict requires a production build (phase A). The GREEN under the lock is the deterministic verdict; each gate keeps it trustworthy. ## Reporting to the user This loop is meant to run unattended, so it doesn't stop to ask between steps. Work the navigation the user named, finish it, and stop. What matters is how you word and present the results, not how often you interrupt. The mechanics below — the rig, RED, GREEN, the gates — are your scaffolding; the user never needs to hear those words. - **Speak their language.** Describe the gap and the result in terms of what the user sees: "navigating to the dashboard waited on the charts query before anything painted; now the layout and skeletons paint instantly and the charts stream in" — not RED/GREEN, the lock, or the phase letters. - **Show, don't tell.** When you report a route, drive the browser (or attach before/after screenshots) so the user watches the shell commit immediately and the data stream in, rather than reading a claim. Identical before and after means the fix did nothing — roll it back. - **Present a run as a list of results the user can click through** — one line per navigation: the route, what commits instantly, and what streams in — not a transcript of the loop. - **Only surface a question for a genuine fork:** a fix that would change behavior, a security-sensitive read, or a route that's dynamic by design (a per-link-prefetch candidate, not a shell to grow). A clean instant fix is not a fork — keep going. With no one to ask (an unattended run), don't block: take the safe default and note the assumption — for a cache-freshness choice, defer the read behind `` (always fresh, still instant) rather than guess a `cacheLife`. ## The workflow ``` - [ ] P PREREQS Next.js 16.3+ with cacheComponents: true; upgrade first → below - [ ] 0 SETUP once per repo: discover + write instant-nav.rig.md → rig-template.md - [ ] A RIG production build with the testing API exposed → below - [ ] B BASELINE unlocked: the marker renders for the test user → test-template.md - [ ] C RED locked instant(): the shell does not commit → test-template.md - [ ] C-gate VERIFY-RED: stop until the RED is trustworthy → reference/red-test-robustness.md - [ ] D FIX apply the matching documented pattern → guide links below - [ ] D1 reuse existing loading UI; keep the shell meaningful - [ ] D2 preserve layout and responsive behavior - [ ] E PARITY the refactor changed only whether the route is instant - [ ] F DIFFERENTIAL revert only the fix → RED; re-apply → GREEN → reference/red-test-robustness.md - [ ] G REVIEW PR checklist (below) ``` Phases B and C build the test; only the locked test from C ships. --- ## P. PREREQUISITES: current Next.js with Cache Components The workflow depends on framework capabilities that ship with current Next.js: - **Next.js 16.3+ with `cacheComponents: true`** in `next.config.ts`. Without Cache Components there is no static shell to optimize. - **`@next/playwright`** on the same release line as the project's `next`; it provides `instant()`. Verify with `npm ls next @next/playwright` (or the project's package manager) and align them if they differ. The matching testing API is in the `next` runtime, gated by the [`experimental.exposeTestingApiInProductionBuild`](https://nextjs.org/docs/app/api-reference/config/next-config-js/exposeTestingApiInProductionBuild) config flag (phase A). If the project does not meet these, upgrade first (`npx @next/codemod upgrade` automates most of it), then enable Cache Components in `next.config.ts`: ```ts export default { cacheComponents: true } ``` Enabling the flag surfaces the blocking routes to resolve first; the [`next-cache-components-adoption`](https://github.com/vercel/next.js/tree/canary/skills/next-cache-components-adoption) skill drives that adoption. Reach for this optimizer once the app builds under Cache Components. This gate is deliberate: the skill targets current Next.js, and none of the verdicts below are meaningful on older versions. ## 0. SETUP: discover this project's rig, once per repo The principles in this skill are fixed; the infrastructure they run on is yours. On first use in a repository, discover how the project builds, deploys, authenticates, and tests (inspect the repository first, and ask the user only what it cannot answer), then write the answers to a committed `instant-nav.rig.md`. Every later run reads that file instead of rediscovering. The required build, test context, navigation contracts, iteration loop, and file template are in **`rig-template.md`**. If the repo has no Playwright e2e harness yet, standing up a minimal one (`@next/playwright`, a config with `baseURL`, one authenticated path) is part of this step; the loop does not assume a pre-existing suite. ## A. RIG: a production build with the testing API exposed Stand up the rig described by `instant-nav.rig.md`. Two invariants hold on every platform: 1. **Never measure on `next dev`.** It does not prefetch, and its lock is unreliable for blocking routes, so a dev `instant()` result is not a valid RED or GREEN. 2. **The measured build must expose the testing API.** Otherwise `instant()` silently no-ops and the test passes vacuously (see `reference/red-test-robustness.md`). The lock-engagement proof is the phase-C RED itself: the unfixed target route is the known-blocking route, and its RED under the lock shows the lock engages on this build (C-gate); the self-validating variant in `test-template.md` is the in-band guarantee. Wire `experimental.exposeTestingApiInProductionBuild` to a condition that is true for every build you measure and never true in production: ```ts experimental: { // Use the condition your platform provides, and record it in the rig file: // local: an explicit opt-in, as below // generic CI: process.env.DEPLOY_ENV === 'staging' // Vercel: process.env.VERCEL_ENV === 'preview' exposeTestingApiInProductionBuild: process.env.EXPOSE_TESTING_API === '1', } ``` The rig is any production-like build that exposes the testing API: a local `next build && next start`, a CI/staging container, and a preview deploy are all equally valid; the verdict comes from the build, not the platform. See `rig-template.md` for the setup requirements. For any deployed or remote build, poll the rig's LIVENESS probe to confirm the artifact contains `HEAD` before trusting a verdict (a stale deploy reads as a false RED or GREEN); a local `next build && next start` needs none. The probe mechanism is in `rig-template.md`. ## B. BASELINE (unlocked): development scaffold, do not ship Drive the real navigation with no `instant()` lock and assert that the destination's `SHELL_MARKER` renders **as the test user**: the account the e2e suite authenticates as (in CI, the CI account; locally, your e2e login fixture), with its flags, plan, role, and data. This establishes that the marker is real and reachable: not flag-gated, not redirected away, not a guessed selector. The suite runs as the test account, not the author's session; that environment drift (the rig DRIFT list) is a common source of untrustworthy REDs. Scaffold and run command: **`test-template.md`**. **Delete this baseline before the PR.** ## C. RED (locked) + the VERIFY-RED gate Wrap the same navigation in `instant()`; assert the shell commits under the lock. A RED here is the gap. **This is the test that ships** (`test-template.md`). Assert the complete intended contract: meaningful shell markers and existing loading states are visible, request-time UI is absent under the lock, and the completed UI renders after release. Do not change an existing data source, production selector, or required route variant to make the test easier. A required contract may not be skipped or weakened. Prefer the self-validating variant when the route has deferred content. If the route cannot build while blocked, or a cookie/session read stays GREEN, use the RED recipes in `reference/red-test-robustness.md`. > **C-gate: do not start optimizing until the RED is verified trustworthy.** A > RED that is red for the wrong reason sends you optimizing a route that was > never broken. The question that settles it: **does `SHELL_MARKER` render without the lock, as the test user?** Answer it by re-running phase B as the test user, not by adding assertions to the shipped test. The two-branch resolution (No → marker or environment bug; Yes → genuine gap, proceed to D), the full taxonomy of untrustworthy REDs, the checklist, and worked cases are in **`reference/red-test-robustness.md`**. Read it now. --- ## D. FIX: apply the documented pattern Use the **Optimizing the static shell** guide you read at the start. Follow the section that matches the blocker instead of duplicating its framework guidance here: | Blocker | Guide pattern | | -------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------- | | Stable UI is hidden by a broader loading state | [Keep static UI in the shell](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#keep-static-ui-in-the-shell) | | A layout or page awaits request-time data too high in the tree | [Push data access down](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#push-data-access-down) | | New or moved boundaries need useful, stable fallbacks | [Design loading states](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#design-loading-states) | | A result can be safely reused across requests | [Cache reusable work](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#cache-reusable-work) | The guide's example covers the common implementation shapes: - [`params`, `searchParams`, and focused boundaries](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#step-1-move-url-dependent-work-behind-suspense) - [authentication, `cookies()`, and `headers()`](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#step-2-move-authentication-behind-suspense) - [cache placement and revalidation](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#step-3-cache-the-reusable-plan-data) Preserve the route's existing data source, freshness, authorization, and completed behavior. Do not replace a mutable read with a build-time import to make it appear static. Cache the existing read when it can be reused. Stream it when it must be computed for each request. If development or a build surfaces another instant-navigation Insight during the refactor, follow [validation as you refactor](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#follow-validation-as-you-refactor) and then the canonical Insight it provides. This is especially important for API-specific blockers such as metadata, viewport, and nondeterministic values. Reuse existing loading UI and keep the resulting shell meaningful at every supported breakpoint. An empty fallback is valid only when the resolved component also has no visual footprint. If the optimization adds or expands a cache boundary, follow [Revalidating](https://nextjs.org/docs/app/getting-started/revalidating). When a writer can change the cached data, populate the cache, perform the mutation, and verify that the next read returns the updated value. `instant()` proves readiness, not mutation freshness. Do not use `export const instant = false`, weaken the contract, or ship an empty document shell as the optimization. > **D-gate: phase D is complete when the locked test from phase C passes GREEN > under the lock on the production-build rig**, not when the code compiles. That > GREEN is the deterministic stop for the fix loop; proceed to E. If URL-specific content is the only missing instant UI, stop at [Include URL-specific content in the instant UI](https://nextjs.org/docs/app/guides/optimizing-the-static-shell#include-url-specific-content-in-the-instant-ui) and hand off to `next-partial-prefetching-optimizer`. ## E. PARITY: the refactor changed only whether the route is instant The push-down is a mechanical transform, not a redesign. Afterward the route must render the same tree, data, ordering, empty and error states, redirects, and interactions as before; the only observable difference is that the shell now commits instantly. Verify: - **Same render output.** The moved `await`s compute and return the same values; after the stream, the route shows the same content as the base branch for the test user. - **Request inputs still work.** Exercise the authentication, cookie, parameter, search-parameter, and data variants named by the route or rig. - **Side effects still fire.** A deferred `redirect()` or `notFound()` still happens at request time. Confirm unauthorized and missing-record behavior. If the route must preserve an HTTP status, account for [streaming status-code behavior](https://nextjs.org/docs/app/guides/streaming#status-codes). - **Supported viewports reach the real UI** after the stream. - **Client state survives.** Because the layout UI is hoisted into the stable shell rather than swapped on resolve, open menus, scroll position, focus, and input state persist across the stream. See [Preserving UI state](https://nextjs.org/docs/app/guides/preserving-ui-state). - **Pre-existing failures stay separate.** If the route errors after the change, reproduce it on the base branch. The same failure there is an environment or data problem, not an optimizer regression. If anything other than whether the route is instant changed, reduce the refactor. ## F. DIFFERENTIAL Revert only the fix → RED; re-apply → GREEN; link both runs (`reference/red-test-robustness.md`). Every contract intended to distinguish the optimization must be RED after the revert and GREEN after the re-apply. On a deployed rig, confirm each run is live (LIVENESS, phase A) before trusting its color. After the final re-apply, run the complete in-scope command from the rig. A filtered subset, a written command, or a suite with a required test skipped is not final GREEN. ## G. REVIEW (PR checklist) A green final state means nothing if the RED was never trustworthy. The test-trustworthiness items are the robustness checklist (`reference/red-test-robustness.md`); confirm them, then require these PR-specific items: - [ ] **Differential shown**: RED without the fix, GREEN with it, runs linked. - [ ] **Parity confirmed (E)**: same content, redirects, and state. - [ ] **Mutations verified when applicable**: after populating any cache whose data can be updated, a mutation test confirms the next read returns the expected data. - [ ] **Freshness preserved**: new cache scopes follow the data's existing or explicitly chosen lifetime. - [ ] **Existing loading UI reused (D1)**: no new page-mirroring skeleton. - [ ] **Shell matches the real render at supported viewports (D2)**. - [ ] **Baseline removed**: only the locked test from C remains. **Stop condition for the whole workflow:** the locked test from C is GREEN on the rig, the differential (F) holds, and every item above is checked. Until all three hold, you are not done. ## Driving the navigation in tests - **Soft navigation** → drive a real `` click. **Initial load** → use `page.goto()` inside `instant()` with the `baseURL` option. Do not substitute `goto` for a soft-nav verdict; the two contracts can differ (`test-template.md`). - With parallel routes, only the slots that change re-render on a soft navigation; client-rendered navigation UI does not re-render at all. Do not chase a slot the navigation never touches. See [Loading and Error UI with Parallel Routes](https://nextjs.org/docs/app/api-reference/file-conventions/parallel-routes#loading-and-error-ui). ## Files - `rig-template.md`: phase 0 production build, test context, navigation contract, and unattended loop discovery. - `test-template.md`: the shipped `instant()` specs for both navigation types (phase C), and the delete-before-PR baseline scaffold (phase B). - `reference/red-test-robustness.md`: the C-gate and phase F. The taxonomy of untrustworthy REDs, the checklist, the differential recipe, the vacuous-pass failure mode, and worked cases. ## After optimization Once the target routes are instant, check whether the app has already adopted Partial Prefetching (`partialPrefetching: true`, or the relevant destination still uses `prefetch = 'partial'` during an incremental rollout). Make that check mechanically: ```bash rg -n "partialPrefetching|prefetch\s*=\s*['\"]partial['\"]" --glob 'next.config.*' --glob 'app/**' --glob 'src/app/**' ``` If `partialPrefetching: true` is in config, the app is globally adopted. If only `prefetch = 'partial'` matches, treat those destination segments as adopted during an incremental rollout and keep checking any other target routes. - **Already adopted:** when the requested instant UI is URL-specific and the destination App Shell is already instant, continue with `next-partial-prefetching-optimizer`. It owns the per-link value and cost decision. - **Not adopted yet:** recommend [`next-partial-prefetching-adoption`](https://github.com/vercel/next.js/tree/canary/skills/next-partial-prefetching-adoption). That skill moves the app onto the better prefetching model: shared App Shell prefetches by default, fewer duplicated full-prefetch requests for visible links, a link audit for existing `` usage, and optional per-link prefetching only where URL-specific content is worth the extra server work.