stalescope

Next.js App Router cache inspector. Drop it in, visit /__stalescope, see exactly which cache layer served every request — live.

Why

Next.js has four separate cache layers. The only built-in debug tool is NEXT_PRIVATE_DEBUG_CACHE — a raw env var dumping unstructured console logs. When your page shows stale data, you have no structured way to see which layer is responsible.

stalescope instruments your fetch calls and revalidations, stores the events in a ring buffer, and renders a live dashboard inside your own app.

Install

npm install stalescope

Setup (two files)

instrumentation.ts (project root):

import { withStalescope } from 'stalescope'
withStalescope()

app/%5F%5Fstalescope/[[...path]]/route.ts:

export { GET, DELETE } from 'stalescope/dashboard'

Next.js treats folders starting with _ as private, non-routable segments — %5F is the URL-encoded underscore, and this folder name maps to the /__stalescope URL at request time.

Visit http://localhost:3000/__stalescope — done.

What you see

• Every fetch() call with status (HIT / MISS / REVALIDATE / SKIP), cache layer, duration, and URL
• Every revalidatePath and revalidateTag call
• Heap usage trend chart — helps correlate memory growth with specific fetch patterns (relevant to the known standalone mode memory leak in Next.js 14-16)
• Live SSE feed — updates without page refresh
• Filter by status, layer, or revalidation type

Options

withStalescope({
  enabled:      true,           // default: NODE_ENV !== 'production'
  maxEvents:    500,            // ring buffer size
  trackMemory:  true,           // log heapUsed per event
  mountPath:    '/__stalescope' // dashboard URL
})

Security

Disable in production (the default). The dashboard exposes internal cache state and heap metrics — not suitable for public exposure.

Related issues

This package was built in response to these open Next.js issues:

• #90433 — Memory leak causing OOM in standalone + fetch
• #85914 — Memory leak Node 22 + fetch + output: standalone
• #75314 — Excessive caching causes memory leak
• #75686 — Memory leak in standalone mode via dedupeFetch
• #68636 — Possible memory leak in Fetch API
• #26801 — Memory leak in Kubernetes (5 years of reports)

License

MIT