A guide for observing a web interface after it is released. It covers error tracking, performance measurements, product-usage events, and alerts, including tools such as Sentry and OpenTelemetry.

Use it to add error boundaries, report frontend failures, monitor Core Web Vitals, track important actions such as signups or checkout, and create alerts.

It provides evidence about errors and slow pages that local testing may miss. It also helps teams notice rising error rates or performance problems in production.

monitoring — Skill for Claude Code by sukirman1901

Install

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.

Any agent

npx skills add sukirman1901/frontend-expert --skill monitoring

Clone the repo

git clone --depth 1 https://github.com/sukirman1901/frontend-expert

Made for: Claude Code.

Or install frontend-expert, the plugin that ships this one along with the rest of its 25 skills, 5 commands, 3 agents, 2 hooks.

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/skills/sukirman1901/frontend-expert/monitoring.svg)](https://agentmods.dev/skills/sukirman1901/frontend-expert/monitoring)

Your own site

<a href="https://agentmods.dev/skills/sukirman1901/frontend-expert/monitoring"><img src="https://agentmods.dev/badge/skills/sukirman1901/frontend-expert/monitoring.svg" alt="Measured on agentmods" height="20"></a>

Per session 65 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 546 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	$0.00065	$0.00546
Opus 5	$0.00032	$0.00273
Sonnet 5	$0.00013	$0.00109
Haiku 4.5	$0.00006	$0.00055

Measured 7d ago against content hash 1519b6427fab, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

monitoring 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.

skills/monitoring/SKILL.md · 65 lines

What it actually says

Monitoring

Overview

Ship UI with enough production signal: errors, performance, and product analytics — without boiling the ocean.

When to use

Add/fix Sentry (or similar) + error boundaries
Performance monitoring / CWV in production
Analytics events for key UI flows
Alerting on error spikes or CWV regressions

When to skip

Pure visual polish (ui-feel / /polish)
Local-only prototypes with no deploy target

MUST (when adding observability)

Signal	Minimum
Errors	Boundary on app shell / critical routes + reporting; scrub PII
Secrets	DSN / keys via env — never commit
Sample rates	Sane defaults for traffic (don’t 100% trace huge apps blindly)
Analytics	Few high-value events (signup, checkout, critical CTA) — not every click
Alerts	Error rate or CWV budget with a named owner

Lab Lighthouse ≠ production monitoring — use fe-devtools for local audits; this skill for shipped signal.

Workflow

Errors — boundary + reporting; scrub PII
Performance — sample traces; watch LCP/INP/CLS on key routes
Analytics — few high-value events, not every click
Alert — error rate / CWV budgets that someone will actually see

Agent boundaries

May decide: Vendor (Sentry vs other), which 3–5 analytics events matter
Must not: Hardcode DSNs; log emails/tokens; add analytics spam on every hover

Checklist

Error boundary on app shell / critical routes
DSN/env via env vars — not hardcoded secrets in git
Sample rates sane for traffic
No PII in events by default
Alerts have an owner
Key product events listed (not clickstream noise)

Depth

Full guide: references/monitoring.md.
Related: web-performance for build-time CWV; fe-devtools for lab audits.

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.

7d ago First seen · 65 lines · 65 tokens per session scan A 1519b6427fab

Subscribe to this mod's changes

monitoring is a skill published in the GitHub repository sukirman1901/frontend-expert (10 stars, last pushed 3d ago), licensed MIT. It adds 65 tokens to every session and 546 once invoked, about $0.0003 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 2026-08-31.

Analytics and metrics Frontend

debug-optimize-lcp

Guides debugging and optimizing Largest Contentful Paint (LCP) using Chrome DevTools MCP tools. Use this skill whenever the user asks about LCP performance, slow page loads, Core Web Vitals optimization, or wants to understand why their page's main content takes too long to appear. Also use when the user mentions…

ChromeDevTools/chrome-devtools-mcp · 99 tokens

repro-admin

Reproduce an EmDash admin UI bug. Attach a container, start the demo dev server, drive the admin with agent-browser using the dev-bypass session, and capture the reproduction as screenshots plus a replayable transcript.

emdash-cms/emdash · 48 tokens

create-site

Creates a new Power Pages code site (SPA) using React, Angular, Vue, or Astro. Guides through the full process from initial concept to deployed site: requirements discovery, scaffolding, component planning, design, implementation, validation, and deployment. Use when the user wants to create, build, or scaffold a new…

microsoft/power-platform-skills · 73 tokens

prototype-web

A clickable, high-fidelity web product prototype with navigation, a hero section, feature cards, steps, social proof, and optional pricing. It is designed to resemble a finished landing page while remaining a prototype.

nexu-io/html-anything · 24 tokens

menu-transitions-rtl

Animate react-horizontal-scrolling-menu scrolling and build right-to-left menus: noPolyfill defaults to true since v8, so transitionDuration (default 500), a custom-easing-function transitionBehavior, and per-call ScrollOptions { duration, boundary } on scrollToItem/scrollNext/scrollPrev are silently ignored unless…

asmyshlyaev177/react-horizontal-scrolling-menu · 137 tokens

vite

Vite build tool configuration, plugin API, SSR, and Vite 8 Rolldown migration. Use when working with Vite projects, vite.config.ts, Vite plugins, or building libraries/SSR apps with Vite.

antfu/skills · 49 tokens