Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/vercel/next.js/insight-error-pagenpx skills add vercel/next.js --skill insight-error-pagegit 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.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00083 | $0.04994 |
| Opus 5 | $0.00042 | $0.02497 |
| Sonnet 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 4d 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.
- 4d 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 (142,020 stars, last pushed 4d ago), licensed MIT. It adds 83 tokens to every session and 4,994 once invoked, about $0.0004 per session on Opus 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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