style: format debug optimize lcp skill

matthiasrohmer · matthiasrohmer · commit 7e6f29a7f80e · 2026-02-23T14:47:51.000+01:00
diff --git a/skills/debug-optimize-lcp/SKILL.md b/skills/debug-optimize-lcp/SKILL.md
@@ -17,12 +17,12 @@ LCP is a Core Web Vital that directly affects user experience and search ranking
 
 Every page's LCP breaks down into four sequential subparts with no gaps or overlaps. Understanding which subpart is the bottleneck is the key to effective optimization.
 
-| Subpart | Ideal % of LCP | What it measures |
-|---------|---------------|------------------|
-| **Time to First Byte (TTFB)** | ~40% | Navigation start → first byte of HTML received |
-| **Resource load delay** | <10% | TTFB → browser starts loading the LCP resource |
-| **Resource load duration** | ~40% | Time to download the LCP resource |
-| **Element render delay** | <10% | LCP resource downloaded → LCP element rendered |
+| Subpart                       | Ideal % of LCP | What it measures                               |
+| ----------------------------- | -------------- | ---------------------------------------------- |
+| **Time to First Byte (TTFB)** | ~40%           | Navigation start → first byte of HTML received |
+| **Resource load delay**       | <10%           | TTFB → browser starts loading the LCP resource |
+| **Resource load duration**    | ~40%           | Time to download the LCP resource              |
+| **Element render delay**      | <10%           | LCP resource downloaded → LCP element rendered |
 
 The "delay" subparts should be as close to zero as possible. If either delay subpart is large relative to the total LCP, that's the first place to optimize.
 
@@ -66,6 +66,7 @@ Use `list_network_requests` to see when the LCP resource loaded relative to othe
 - Then use `get_network_request` with the LCP resource's request ID for full details.
 
 **Key Checks:**
+
 - **Start Time**: Compare against the HTML document and the first resource. If the LCP resource starts much later than the first resource, there's resource load delay to eliminate.
 - **Duration**: A large resource load duration suggests the file is too big or the server is slow.
 
@@ -78,28 +79,36 @@ Use `evaluate_script` with the **"Audit Common Issues" snippet** found in [refer
 After identifying the bottleneck subpart, apply these prioritized fixes.
 
 ### 1. Eliminate Resource Load Delay (target: <10%)
+
 The most common bottleneck. The LCP resource should start loading immediately.
+
 - **Root Cause**: LCP image loaded via JS/CSS, `data-src` usage, or `loading="lazy"`.
 - **Fix**: Use standard `<img>` with `src`. **Never** lazy-load the LCP image.
 - **Fix**: Add `<link rel="preload" fetchpriority="high">` if the image isn't discoverable in HTML.
 - **Fix**: Add `fetchpriority="high"` to the LCP `<img>` tag.
 
 ### 2. Eliminate Element Render Delay (target: <10%)
+
 The element should render immediately after loading.
+
 - **Root Cause**: Large stylesheets, synchronous scripts in `<head>`, or main thread blocking.
 - **Fix**: Inline critical CSS, defer non-critical CSS/JS.
 - **Fix**: Break up long tasks blocking the main thread.
 - **Fix**: Use Server-Side Rendering (SSR) so the element exists in initial HTML.
 
 ### 3. Reduce Resource Load Duration (target: ~40%)
+
 Make the resource smaller or faster to deliver.
+
 - **Fix**: Use modern formats (WebP, AVIF) and responsive images (`srcset`).
 - **Fix**: Serve from a CDN.
 - **Fix**: Set `Cache-Control` headers.
 - **Fix**: Use `font-display: swap` if LCP is text blocked by a web font.
 
 ### 4. Reduce TTFB (target: ~40%)
+
 The HTML document itself takes too long to arrive.
+
 - **Fix**: Minimize redirects and optimize server response time.
 - **Fix**: Cache HTML at the edge (CDN).
 - **Fix**: Ensure pages are eligible for back/forward cache (bfcache).
diff --git a/skills/debug-optimize-lcp/references/lcp-breakdown.md b/skills/debug-optimize-lcp/references/lcp-breakdown.md
@@ -6,12 +6,12 @@ LCP measures the time from when the user initiates loading the page until the la
 
 Every page's LCP consists of these four subcategories. There's no gap or overlap between them, and they add up to the full LCP time.
 
-| LCP subpart | % of LCP (Optimal) | Description |
-|---|---|---|
-| **Time to First Byte (TTFB)** | ~40% | The time from when the user initiates loading the page until the browser receives the first byte of the HTML document response. |
-| **Resource load delay** | <10% | The time between TTFB and when the browser starts loading the LCP resource. If the LCP element doesn't require a resource load (e.g., system font text), this time is 0. |
-| **Resource load duration** | ~40% | The duration of time it takes to load the LCP resource itself. If the LCP element doesn't require a resource load, this time is 0. |
-| **Element render delay** | <10% | The time between when the LCP resource finishes loading and the LCP element rendering fully. |
+| LCP subpart                   | % of LCP (Optimal) | Description                                                                                                                                                              |
+| ----------------------------- | ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
+| **Time to First Byte (TTFB)** | ~40%               | The time from when the user initiates loading the page until the browser receives the first byte of the HTML document response.                                          |
+| **Resource load delay**       | <10%               | The time between TTFB and when the browser starts loading the LCP resource. If the LCP element doesn't require a resource load (e.g., system font text), this time is 0. |
+| **Resource load duration**    | ~40%               | The duration of time it takes to load the LCP resource itself. If the LCP element doesn't require a resource load, this time is 0.                                       |
+| **Element render delay**      | <10%               | The time between when the LCP resource finishes loading and the LCP element rendering fully.                                                                             |
 
 ## Why the Breakdown Matters
 
diff --git a/skills/debug-optimize-lcp/references/lcp-snippets.md b/skills/debug-optimize-lcp/references/lcp-snippets.md
@@ -3,12 +3,13 @@
 Use these JavaScript snippets with the `evaluate_script` tool to extract deep insights from the page.
 
 ## 1. Identify LCP Element
+
 Use this snippet to identify the LCP element and get raw timing data from the Performance API.
 
 ```javascript
 async () => {
-  return await new Promise((resolve) => {
-    new PerformanceObserver((list) => {
+  return await new Promise(resolve => {
+    new PerformanceObserver(list => {
       const entries = list.getEntries();
       const last = entries[entries.length - 1];
       resolve({
@@ -21,12 +22,13 @@ async () => {
         loadTime: last.loadTime,
         size: last.size,
       });
-    }).observe({ type: 'largest-contentful-paint', buffered: true });
+    }).observe({type: 'largest-contentful-paint', buffered: true});
   });
-}
+};
 ```
 
 ## 2. Audit Common Issues
+
 Use this snippet to check for common DOM-based LCP issues (lazy loading, priority).
 
 ```javascript
@@ -40,7 +42,7 @@ Use this snippet to check for common DOM-based LCP issues (lazy loading, priorit
       issues.push({
         issue: 'lazy-loaded image in viewport',
         element: img.outerHTML.substring(0, 200),
-        fix: 'Remove loading="lazy" from this image — it is in the initial viewport and may be the LCP element'
+        fix: 'Remove loading="lazy" from this image — it is in the initial viewport and may be the LCP element',
       });
     }
   });
@@ -52,23 +54,26 @@ Use this snippet to check for common DOM-based LCP issues (lazy loading, priorit
       issues.push({
         issue: 'large viewport image without fetchpriority',
         element: img.outerHTML.substring(0, 200),
-        fix: 'Add fetchpriority="high" to this image — it is large and visible in the initial viewport'
+        fix: 'Add fetchpriority="high" to this image — it is large and visible in the initial viewport',
       });
     }
   });
 
   // Check for render-blocking scripts in head
-  document.querySelectorAll('head script:not([async]):not([defer]):not([type="module"])')
+  document
+    .querySelectorAll(
+      'head script:not([async]):not([defer]):not([type="module"])',
+    )
     .forEach(script => {
       if (script.src) {
         issues.push({
           issue: 'render-blocking script in head',
           element: script.outerHTML.substring(0, 200),
-          fix: 'Add async or defer attribute, or move to end of body'
+          fix: 'Add async or defer attribute, or move to end of body',
         });
       }
     });
 
-  return { issueCount: issues.length, issues };
-}
+  return {issueCount: issues.length, issues};
+};
 ```
diff --git a/skills/debug-optimize-lcp/references/optimization-strategies.md b/skills/debug-optimize-lcp/references/optimization-strategies.md
@@ -1,6 +1,7 @@
 # LCP Optimization Strategies
 
 ## 1. Eliminate Resource Load Delay
+
 **Goal**: Ensure the LCP resource starts loading as early as possible.
 
 - **Early Discovery**: Ensure the LCP resource is discoverable in the initial HTML document response (not dynamically added by JS or hidden in `data-src`).
@@ -10,6 +11,7 @@
 - **Same Origin**: Host critical resources on the same origin or use `<link rel="preconnect">`.
 
 ## 2. Eliminate Element Render Delay
+
 **Goal**: Ensure the LCP element can render immediately after its resource has finished loading.
 
 - **Minimize Render-Blocking CSS**: Inline critical CSS and defer non-critical CSS. Ensure the stylesheet is smaller than the LCP resource.
@@ -18,6 +20,7 @@
 - **Break Up Long Tasks**: Prevent large JavaScript tasks from blocking the main thread during rendering.
 
 ## 3. Reduce Resource Load Duration
+
 **Goal**: Reduce the time spent transferring the bytes of the resource.
 
 - **Optimize Resource Size**: Serve optimal image sizes, use modern formats (AVIF, WebP), and compress images/fonts.
@@ -26,6 +29,7 @@
 - **Caching**: Use efficient `Cache-Control` policies.
 
 ## 4. Reduce Time to First Byte (TTFB)
+
 **Goal**: Deliver the initial HTML as quickly as possible.
 
 - **Minimize Redirects**: Avoid multiple redirects from advertisements or shortened links.
