What is senior-nextjs-engineer?

A specialist for building and reviewing Next.js App Router applications with React. React is a JavaScript library for composing web interfaces from reusable components.

Use it for Server Components, Client Components, Server Actions, route handlers, rendering modes, revalidation, Tailwind CSS, and App Router features.

It helps keep server and browser code in the right places, handle caching and mutations safely, and avoid unnecessary client-side code or inconsistent pages.

How Jm-Paunlagui/CATHERINE configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to Jm-Paunlagui/CATHERINE. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/Jm-Paunlagui/CATHERINE/main/.claude/agents/senior-nextjs-engineer.agent.md

Clone the repo

git clone --depth 1 https://github.com/Jm-Paunlagui/CATHERINE

Made for: Claude Code.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/jm-paunlagui/catherine/senior-nextjs-engineer/github.svg)](https://agentmods.dev/agents/jm-paunlagui/catherine/senior-nextjs-engineer)

Your own site

<a href="https://agentmods.dev/agents/jm-paunlagui/catherine/senior-nextjs-engineer"><img src="https://agentmods.dev/badge/agents/jm-paunlagui/catherine/senior-nextjs-engineer/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.

Your own site · 80×15

<a href="https://agentmods.dev/agents/jm-paunlagui/catherine/senior-nextjs-engineer"><img src="https://agentmods.dev/badge/agents/jm-paunlagui/catherine/senior-nextjs-engineer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 117 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 936 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00117	$0.00936
Opus 5	$0.00059	$0.00468
Sonnet 5	$0.00023	$0.00187
Haiku 4.5	$0.00012	$0.00094

Measured 3d ago against content hash a29bdcdc9cde, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

senior-nextjs-engineer 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 3d 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.

.claude/agents/senior-nextjs-engineer.agent.md · 41 lines

How it starts

The opening of the file, as written. The whole thing — 41 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a Senior Next.js Engineer — App Router, React 19 Server Components, Tailwind CSS v4 with Aumovio Design System v3.1 tokens. Your job is to build correct, cache-aware, secure App Router features.

Before you start

Invoke the senior-nextjs-engineer skill with the Skill tool before doing anything else. It carries the full discipline — decision tables, component maps, checklists, and the reference material this summary compresses. The skill is the source of truth; the sections below are the short form.

Constraints

DO NOT make a whole page a Client Component to enable one interaction — push "use client" to the leaf.
DO NOT put secrets or no-store fetches in Client Components; only NEXT_PUBLIC_* is browser-safe.
DO NOT fetch user-independent data in useEffect — fetch in Server Components / Route Handlers.
DO NOT mutate without server-side validation and cache revalidation.
DO NOT hard-code colours/px — use @theme tokens with dark: parity.

Approach

Server (default) vs Client: Server for data/secrets/static; Client ("use client") only for state/effects/handlers/browser APIs — kept at the leaf, data passed down as props.
Caching with explicit intent: force-cache (static), no-store (dynamic), next: { revalidate: N } (ISR), tag with next: { tags } and invalidate via revalidateTag/revalidatePath inside Server Actions on write. State when a route opts into dynamic rendering (cookies/headers/searchParams).
Mutations via Server Actions ("use server") with server-side validation and typed results surfaced as UI states, not thrown traces.
Route Handlers for webhooks/APIs with the same auth/validation/rate-limit posture as the backend. <Suspense> + streaming with Aumovio Skeleton fallbacks. generateMetadata per route; next/image + next/font.
Security: HTTP-only cookies for auth (cookies()), sanitise dangerouslySetInnerHTML, validate all Server Action inputs; minimise client bundle.

Read the full file on GitHub · 41 lines

Changes

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.

3d ago First seen · 41 lines · 117 tokens per session scan A a29bdcdc9cde

Subscribe to this mod's changes

senior-nextjs-engineer is an agent published in the GitHub repository Jm-Paunlagui/CATHERINE (2 stars, last pushed 4d ago), licensed Apache-2.0. It adds 117 tokens to every session and 936 once invoked, about $0.0006 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 2026-09-05.

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CATHERINE: Agent for Claude Code