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 skills add kostja94/marketing-skills --skill 404git clone --depth 1 https://github.com/kostja94/marketing-skillsWrote 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/kostja94/marketing-skills/404)<a href="https://agentmods.dev/skills/kostja94/marketing-skills/404"><img src="https://agentmods.dev/badge/skills/kostja94/marketing-skills/404/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/kostja94/marketing-skills/404"><img src="https://agentmods.dev/badge/skills/kostja94/marketing-skills/404.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00082 | $0.00676 |
| Opus 5 | $0.00041 | $0.00338 |
| Sonnet 5 | $0.00016 | $0.00135 |
| Haiku 4.5 | $0.00008 | $0.00068 |
Grade A, and why
404-page-generator 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 7d 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.
Copies of this mod
2 near-identical copies found in the catalogue:
- 404-page-generator — 100% identical, 0 lines differ
- 404-page-generator — 100% identical, 0 lines differ
How it starts
The opening of the file, as written. The whole thing — 74 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Pages: 404 Error Page
Guides 404 error page design for UX, conversion recovery, and brand consistency.
When invoking: On first use, if helpful, open with 1-2 sentences on what this skill covers and why it matters, then provide the main output. On subsequent use or when the user asks to skip, go directly to the main output.
Initial Assessment
Check for project context first: If .claude/project-context.md or .cursor/project-context.md exists, read it for brand voice, key pages, and Section 12 (Visual Identity).
Identify:
- Site structure: Key pages to link (homepage, popular pages, search)
- Brand tone: Friendly, professional, playful
- Conversion goal: Recover lost visitors, drive to key pages
Best Practices
Clear Error Messaging
- User-friendly: Neutral message explaining the page wasn't found
- Optional 404 display: Can show "404" but avoid blaming the user
- Empathetic tone: Acknowledge the error gracefully; turn frustration into opportunity
Navigation and Redirection
| Element | Purpose |
|---|---|
| Site navigation | Header/footer so users know they're still on your site |
| Search | Help users find what they need |
| Popular pages | Links to homepage, features, pricing, blog |
| Similar URLs | Suggest corrections for common typos |
| Avoid auto-redirect | Unless confident of user intent |
Design and Branding
- Consistent design: Same header, footer, colors as rest of site (brand-visual-generator)
- Avoid confusion: Users should not think they've left your domain
- Mobile responsive: Test on all devices
Conversion Opportunities
404 pages can drive conversions by:
- Showcasing popular products or features
- Featuring testimonials or social proof
- Offering special promotions or value
- Linking to mobile app or newsletter
Technical
- Track 404s: Monitor broken links, fix or redirect
- Accessibility: Maintain WCAG standards
- HTTP status: Ensure proper 404 response code
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.
- 7d ago First seen · 74 lines · 82 tokens per session scan A cde007e2e506
404-page-generator is a skill published in the GitHub repository kostja94/marketing-skills (963 stars, last pushed 3mo ago), licensed MIT. It adds 82 tokens to every session and 676 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 2026-09-03.
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