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 rules/d-padmanabhan/agent-engineering-handbook/260-frontendgit clone --depth 1 https://github.com/d-padmanabhan/agent-engineering-handbookWrote 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/rules/d-padmanabhan/agent-engineering-handbook/260-frontend)<a href="https://agentmods.dev/rules/d-padmanabhan/agent-engineering-handbook/260-frontend"><img src="https://agentmods.dev/badge/rules/d-padmanabhan/agent-engineering-handbook/260-frontend.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 5.1 | $0.00045 | $0.02410 |
| Opus 5 | $0.00023 | $0.01205 |
| Sonnet 5 | $0.00009 | $0.00482 |
| Haiku 4.5 | $0.00005 | $0.00241 |
Grade A, and why
260-frontend 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 5d 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 — 162 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Frontend Architecture - Cross-cutting Non-Negotiables
Audience: engineers designing, reviewing, or operating browser-facing applications and static sites - regardless of framework (React, Vue, Svelte, Solid, Astro, Next, Nuxt, Gatsby, Hugo, Eleventy, SvelteKit, Remix).
Scope: the choices that apply the same way across frameworks. For framework-specific advice (React Server Components, Vue Composition API, Hugo partials, etc.), defer to the framework's docs and to 999-local-overrides.mdc in each consumer repo. This rule is the cross-cutting layer; the skill frontend-engineering is the depth.
[!IMPORTANT] Frontend rules in this repo are intentionally framework-agnostic. Adding React/Vue/Hugo encyclopedia content here would be shallow guidance authored from docs, not earned from production reviews. Pin framework-specific guidance in
999-local-overrides.mdcper repo.
Non-negotiables
NN1. Rendering choice is made before code lands
SPA / SSG / SSR / ISR / hybrid is an architecture decision, not a default. Document it in an ADR or the README before the first feature commit.
| Pattern | When | Trade-off |
|---|---|---|
| SSG (static site generation) | Content changes less than daily; SEO matters; no per-user state | Cheapest hosting (CDN-only); rebuild on every change |
| SSR (per-request) | Per-user content; SEO matters; freshness matters | Server cost; slower TTFB than SSG if not cached |
| SPA (client-side render) | Internal tools; authenticated apps; no SEO need | Worst TTFB / FCP; bad on slow networks; richest interactivity |
| ISR (incremental SSG) | Mostly-static with occasional updates | SSG cost + on-demand re-render budget |
| Hybrid (RSC, islands, partial hydration) | Mix of above per route | Most complex; biggest payoff at scale |
NN2. Bundle budget per route is enforced in CI
Every PR runs against a budget. PRs that breach are blocked until either the budget is raised (with justification in the PR description) or the code is trimmed. Raising the budget silently is the same anti-pattern as suppressing a test.
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.
- 5d ago First seen · 162 lines · 45 tokens per session scan A bb940e0c698a
260-frontend is a cursor rule published in the GitHub repository d-padmanabhan/agent-engineering-handbook (16 stars, last pushed 5d ago), licensed MIT. It adds 45 tokens to every session and 2,410 once invoked, about $0.0002 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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