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On-Site SEO

On-site SEO is the practice of optimizing individual page elements in code to improve search visibility. This skill is the hands-on implementation companion to the broader SEO strategy skills - it covers everything a developer touches directly: meta tags, headings, images, links, semantic HTML, and social sharing tags. It is framework-aware, with concrete code patterns for Next.js, Nuxt, Astro, and Remix. The focus is on correct, production-grade implementation - not strategy or keyword research.

When to use this skill

Trigger this skill when the user:

• Wants to add or fix meta tags (title, description, canonical, robots)
• Needs to implement Open Graph or Twitter Card tags
• Asks about heading structure (H1, H2, H3 hierarchy) on a page
• Wants to add or improve alt text on images
• Asks how to implement SEO in Next.js, Nuxt, Astro, or Remix
• Needs to optimize images for SEO (alt text, lazy loading, dimensions, format)
• Wants to add semantic HTML to improve page structure
• Asks about internal linking strategy in code

Do NOT trigger this skill for:

• Keyword research or content strategy - use keyword-research skill instead
• Performance metrics, Largest Contentful Paint, or Core Web Vitals optimization - use core-web-vitals skill instead

Key principles

1. Title tag is the single most impactful on-page element - Keep it under 60 characters, put the primary keyword near the start, make it unique per page. Every page with a missing or duplicated title tag is leaving ranking signal on the table.

2. One H1 per page, containing the primary keyword - The H1 is the page's editorial headline. More than one H1 confuses search engines about the page's topic. H1 should be distinct from the title tag - not identical - but semantically aligned.

3. Every image needs descriptive alt text - Alt text is read by screen readers and indexed by crawlers. Describe the image's subject and context. Do not keyword- stuff alt text - "golden retriever puppy on grass" beats "dog puppy dog pictures dogs".

4. Internal links distribute authority and aid discovery - Every page on the site should be reachable via internal links. Anchor text should be descriptive, not generic ("see pricing" not "click here"). Use absolute URLs for reliability.

5. Semantic HTML helps search engines understand page structure - Elements like <article>, <nav>, <main>, <section>, <header>, and <footer> communicate document structure to crawlers without extra markup. Use native elements before adding schema markup.

Core concepts

The on-page SEO hierarchy

Search engines weight on-page signals in this order (highest to lowest impact):

title tag       <- URL bar, search snippet title, primary ranking signal
H1              <- editorial headline, should contain primary keyword
meta description <- search snippet body, not a ranking signal but drives CTR
headings (H2-H6) <- content structure, secondary keyword placement
body content    <- relevance signals, LSI keywords, readability
images          <- alt text, filename, lazy loading, dimensions
internal links  <- anchor text, page authority distribution, crawl paths

Meta robots directives

Control crawl behavior with the robots meta tag:

<!-- Default - index the page, follow links -->
<meta name="robots" content="index, follow">

<!-- Block indexing but follow links (e.g. pagination, filtered views) -->
<meta name="robots" content="noindex, follow">

<!-- Block indexing and link following (e.g. admin pages) -->
<meta name="robots" content="noindex, nofollow">

<!-- Allow indexing but don't follow links -->
<meta name="robots" content="index, nofollow">

Open Graph protocol

OG tags control how pages appear when shared on Facebook, LinkedIn, Slack, and most social platforms. The minimum required set:

<meta property="og:title" content="Page Title Here">
<meta property="og:description" content="Description (max 300 chars recommended)">
<meta property="og:image" content="https://example.com/og-image.png">
<meta property="og:url" content="https://example.com/page">
<meta property="og:type" content="website">

OG image should be 1200x630px (1.91:1 ratio). Twitter uses twitter: prefixed tags but falls back to OG tags when Twitter-specific tags are absent.

Canonical URLs

The canonical tag tells search engines which URL is the authoritative version of a page. Required for: paginated content, filtered/sorted product listings, content syndicated across multiple URLs, and HTTPS/HTTP or www/non-www variants.

<link rel="canonical" href="https://example.com/the-original-page">

Semantic HTML5 and SEO value

Common tasks

1. Set up complete meta tags for a page

The minimum complete set for any page:

<head>
  <!-- Title tag - unique per page, primary keyword near start, max 60 chars -->
  <title>Primary Keyword - Brand Name</title>

  <!-- Meta description - not a ranking signal but drives CTR, max 160 chars -->
  <meta name="description" content="Clear description of what this page offers.">

  <!-- Canonical - prevents duplicate content issues -->
  <link rel="canonical" href="https://example.com/page-url">

  <!-- Robots - only needed when deviating from default (index, follow) -->
  <meta name="robots" content="index, follow">
</head>

2. Implement Open Graph and Twitter Card tags

<!-- Open Graph (Facebook, LinkedIn, Slack, iMessage previews) -->
<meta property="og:title" content="Page Title">
<meta property="og:description" content="Page description, max 300 chars.">
<meta property="og:image" content="https://example.com/images/og-1200x630.png">
<meta property="og:image:width" content="1200">
<meta property="og:image:height" content="630">
<meta property="og:image:alt" content="Description of the OG image">
<meta property="og:url" content="https://example.com/page">
<meta property="og:type" content="website">
<meta property="og:site_name" content="Brand Name">

<!-- Twitter Card (falls back to OG if twitter: tags are absent) -->
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:site" content="@twitterhandle">
<meta name="twitter:title" content="Page Title">
<meta name="twitter:description" content="Page description.">
<meta name="twitter:image" content="https://example.com/images/twitter-1200x628.png">
<meta name="twitter:image:alt" content="Description of the Twitter image">

3. Structure headings correctly

Every page needs exactly one H1. Headings should never skip levels (H1 > H3).

<main>
  <h1>Primary Keyword - Page Main Topic</h1>

  <section>
    <h2>First Major Subtopic</h2>
    <p>Content...</p>

    <h3>Supporting Detail Under Subtopic</h3>
    <p>Content...</p>
  </section>

  <section>
    <h2>Second Major Subtopic</h2>
    <p>Content...</p>
  </section>
</main>

Anti-pattern to avoid: using heading tags for visual styling. Use CSS classes instead.

4. Optimize images for SEO

<!-- Full SEO-optimized image tag -->
<img
  src="/images/golden-retriever-puppy.webp"
  alt="Golden retriever puppy playing in grass at sunset"
  width="800"
  height="600"
  loading="lazy"
  decoding="async"
>

<!-- For above-the-fold images: eager loading + fetchpriority -->
<img
  src="/images/hero-banner.webp"
  alt="Team working in a modern office space"
  width="1440"
  height="600"
  loading="eager"
  fetchpriority="high"
>

Image SEO rules:

• Filename should describe content: golden-retriever-puppy.webp not img_0042.jpg
• Always include width and height to prevent layout shift (CLS)
• Use modern formats: WebP or AVIF preferred over JPEG/PNG
• loading="lazy" on below-fold images; loading="eager" on above-fold

5. Build internal linking patterns

<!-- Good: descriptive anchor text, absolute URL -->
<a href="https://example.com/pricing">View our pricing plans</a>

<!-- Good: contextual link in body content -->
<p>
  Learn more about
  <a href="/guides/seo-strategy">technical SEO strategy</a>
  before optimizing individual pages.
</p>

<!-- Bad: generic anchor text -->
<a href="/pricing">click here</a>

<!-- Breadcrumb navigation - also useful for SEO -->
<nav aria-label="Breadcrumb">
  <ol>
    <li><a href="/">Home</a></li>
    <li><a href="/guides">Guides</a></li>
    <li aria-current="page">On-Site SEO</li>
  </ol>
</nav>

6. Add semantic HTML to page structure

<body>
  <header>
    <nav aria-label="Main navigation">
      <!-- Primary site navigation -->
    </nav>
  </header>

  <main>
    <article>
      <header>
        <h1>Article Title</h1>
        <time datetime="2025-03-14">March 14, 2025</time>
      </header>

      <section>
        <h2>Section Heading</h2>
        <p>Section content...</p>
      </section>
    </article>

    <aside>
      <h2>Related Articles</h2>
      <!-- Supplementary content -->
    </aside>
  </main>

  <footer>
    <!-- Site footer -->
  </footer>
</body>

7. Next.js App Router - generateMetadata

// app/blog/[slug]/page.tsx
import type { Metadata } from 'next';

export async function generateMetadata({
  params,
}: {
  params: { slug: string };
}): Promise<Metadata> {
  const post = await fetchPost(params.slug);

  return {
    title: post.title,
    description: post.excerpt,
    alternates: {
      canonical: `https://example.com/blog/${params.slug}`,
    },
    openGraph: {
      title: post.title,
      description: post.excerpt,
      images: [{ url: post.ogImage, width: 1200, height: 630 }],
      type: 'article',
    },
    twitter: {
      card: 'summary_large_image',
      title: post.title,
      description: post.excerpt,
      images: [post.ogImage],
    },
  };
}

8. Nuxt 3 - useSeoMeta

// pages/blog/[slug].vue
<script setup>
const route = useRoute();
const { data: post } = await useFetch(`/api/posts/${route.params.slug}`);

useSeoMeta({
  title: post.value.title,
  description: post.value.excerpt,
  ogTitle: post.value.title,
  ogDescription: post.value.excerpt,
  ogImage: post.value.ogImage,
  ogUrl: `https://example.com/blog/${route.params.slug}`,
  twitterCard: 'summary_large_image',
  twitterTitle: post.value.title,
  twitterDescription: post.value.excerpt,
  twitterImage: post.value.ogImage,
});
</script>

Anti-patterns / common mistakes

Gotchas

1. Next.js generateMetadata does not merge with layout.tsx metadata - If a root layout.tsx defines a metadata export and a page also uses generateMetadata, they do not deep-merge automatically. The page's metadata overrides the layout's at the same key. You must spread the parent metadata explicitly or use metadata.metadataBase at the root level to avoid broken absolute URL generation for OG images.

2. Canonical self-referencing with trailing slash mismatch causes duplicate content - If the server serves both /page and /page/, and the canonical points to only one form, crawlers still see two URLs. Enforce a consistent URL form at the CDN or server level AND set canonical - don't rely on canonical alone to resolve the conflict.

3. OG image URL must be absolute, not relative - og:image content must be a full https:// URL. Relative paths like /images/og.png are not followed by most social crawlers. Always include the full domain, including in framework configurations like Next.js metadataBase.

4. noindex on paginated pages blocks discovery of linked content - Adding noindex to ?page=2 and beyond is a common SEO mistake. Crawlers still follow links from those pages to discover new URLs. The correct approach for pagination is using <link rel="canonical"> pointing to page 1 or letting Google handle pagination discovery naturally.

5. title tag set in JavaScript renders too late for crawlers - Client-side JS that sets document.title after load is not reliably indexed by crawlers or used for social previews. Always set title tags server-side in the <head>, never via document.title = ... after hydration.

References

For detailed framework-specific SEO patterns, load the relevant reference file:

• references/nextjs-seo.md - Next.js App Router Metadata API, generateMetadata, sitemap.ts, robots.ts, dynamic OG images with next/og
• references/nuxt-seo.md - Nuxt 3 useSeoMeta, useHead, nuxt-seo module, OG image generation, sitemap and robots modules
• references/astro-seo.md - Astro SEO component patterns, content collections with frontmatter SEO, sitemap integration, astro-seo package
• references/remix-seo.md - Remix meta function (V2 convention), loader-based dynamic meta, parent route meta merging, canonical URLs

For related skills:

• Load schema-markup skill for JSON-LD structured data implementation
• Load core-web-vitals skill for LCP, CLS, INP performance optimization
• Load technical-seo skill for crawlability, rendering strategy, and site architecture

Companion check

On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:

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npx skills add AbsolutelySkilled/AbsolutelySkilled --skill <name>

Skip entirely if recommended_skills is empty or all companions are already installed.