PrompTom
Alle Skills

Why the page is slow

page-speedPROperformanceoptimisation

Measures first, then fixes — and in the order that actually makes a difference.

Was er tut

  • Triggers on “the site is slow”, “bad Lighthouse score”, “check the speed”.
  • Forbids touching anything before a measurement: guesses about what is slow are usually wrong, and optimising the wrong thing costs a day and moves nothing.
  • Measures on a slow device and a slow connection: a run on a fast machine over fibre says nothing about the phone people actually browse on.
  • Reads three numbers and knows what each blames: largest paint blames an image or a font, layout shift blames something that arrived late without dimensions, interaction delay is almost always JavaScript.
  • Fixes in order: do not send it, send it smaller, send it later, send it sooner. And forbids lazy-loading the largest paint element — that makes the number worse.
  • Requires the number before, the number after, and the device they were measured on. A percentage with no baseline says nothing.
  • Reverts a change that moved nothing: complexity bought for nothing is paid for by whoever reads the code next.

Wozu er gut ist

Speed usually gets fixed by following listicles, which produces a week of work and unchanged numbers. Order matters more than technique here: the fastest asset is the one never requested, and deleting an unused library almost always beats any compression setting. And the classic own goal is lazy-loading the very image the score is computed from.

Wohin damit

  1. 1Legen Sie im Projekt den Ordner .claude/skills/page-speed an
  2. 2Legen Sie dort eine SKILL.md mit dem Text unten ab
  3. 3Fertig. Claude Code lädt den Skill selbst, sobald eine Aufgabe zur Beschreibung passt

Damit der Skill in allen Projekten statt nur in einem funktioniert, legen Sie ihn in ~/.claude/skills statt in den Projektordner.

SKILL.md-Datei

# Making a page fast

Measure before changing anything. Most guesses about what is slow are
wrong, and optimising the wrong thing costs a day and moves nothing.

## Measure the right thing

Field data beats lab data. A Lighthouse run on a fast machine over
fibre says little about a mid-range phone on mobile data, which is what
most visitors are on. If there is no field data, throttle: mid-tier CPU,
slow 4G.

Look at three numbers and know what each blames:

- **Largest paint** — the biggest thing above the fold. Usually an
  image, a webfont, or content waiting on a request.
- **Layout shift** — something arrived late and pushed the page around.
  Almost always an image without dimensions, a late-loading font, or an
  injected banner.
- **Interaction delay** — the main thread is busy. Almost always
  JavaScript.

## Fix in this order

Die Datei dieses Skills gehört zur PRO-Auswahl

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Why the page is slow — PrompTom