Next.js is a React framework for building applications that run across the browser and Node.js, including server-rendered applications. It is used by developers building web applications with React components.
Borrowing it
Nothing to install: this file belongs to vercel/next.js. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/vercel/next.js/canary/.agents/skills/insight-error-page/SKILL.mdgit clone --depth 1 https://github.com/vercel/next.jsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/vercel/next.js/insight-error-page)<a href="https://agentmods.dev/skills/vercel/next.js/insight-error-page"><img src="https://agentmods.dev/badge/skills/vercel/next.js/insight-error-page/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/vercel/next.js/insight-error-page"><img src="https://agentmods.dev/badge/skills/vercel/next.js/insight-error-page.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Snyk pass
- NVIDIA SkillSpector warn
SkillSpector: 2 findings, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Prompt Injection · line 24 Large whitespace padding was detected (a block of blank lines or a long run of spaces). This can push injected instructions below or to the right of the visible area so a human reviewer never sees them while the agent still reads them. Manual review of the hidden content is recommended.Fix: Remove the large whitespace padding (blank-line blocks or long space runs) and review any content hidden below or to the right of it. Keep skill files compact and reviewable so no instructions can be
- medium Prompt Injection · line 24 Large whitespace padding was detected (a block of blank lines or a long run of spaces). This can push injected instructions below or to the right of the visible area so a human reviewer never sees them while the agent still reads them. Manual review of the hidden content is recommended.Fix: Remove the large whitespace padding (blank-line blocks or long space runs) and review any content hidden below or to the right of it. Keep skill files compact and reviewable so no instructions can be
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00083 | $0.04994 |
| Opus 5.5 | $0.00033 | $0.01998 |
| Sonnet 5.5 | $0.00017 | $0.00999 |
| Haiku 4.5 | $0.00008 | $0.00499 |
Grade A, and why
insight-error-page scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 251 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Insight Error Page — Write & Audit
Write or audit an errors/<slug>.mdx insight-kind page that ships from this repo to nextjs.org and mirrors the fix-card set in the Next.js dev overlay.
Terminology: the frontmatter uses
kind: insightbut the body text calls these "errors" — never "insights". Write "this error", "error pages", "dismiss the error".
When to use this skill
- Write mode: "create the error page for
next-prerender-random", "write the sync IO docs" - Audit mode: "audit the blocking-prerender-dynamic page", "check the error pages match the framework"
- Any task involving
errors/*.mdxinsight pages (frontmatter haskind: insight)
Source of truth chain
Every decision traces back to one of these. When in doubt, read the source — don't guess.
| What | Source file | How to read it |
|---|---|---|
| Card titles, IDs, groups, snippets, link URLs | packages/next/src/next-devtools/dev-overlay/components/instant/instant-guidance-data.ts |
Each FixCard[] array is one error family |
| Error headline (literal text user sees) | packages/next/src/server/app-render/sync-io-messages.ts, blocking-route-messages.ts, etc. |
createSyncIOError, createDynamicBodyError, etc. — the template string is the headline |
| Existing page (content to preserve) | errors/<slug>.mdx in this repo |
Read the full file; relocate useful content that doesn't fit fix cards into Gotchas or Other options |
| Canonical API docs (terminology) | docs/01-app/ in this repo |
Cross-check every API name, directive name, and concept against the published docs |
| Template structure | This skill file (below) | The canonical shape of the page |
| Vercel writing style | The vercel-technical-writing skill in vercel/front (not present here) |
Apply end-to-end; see "Voice and style" below for the rules condensed |
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 251 lines · 83 tokens per session scan A 106619cf59b1
insight-error-page is a skill published in the GitHub repository vercel/next.js (143,076 stars, last pushed today), licensed MIT. It adds 83 tokens to every session and 4,994 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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