SEO Foundations Developers Should Know

Understanding On-Page and Off-Page SEO

Before diving into technical specifics, let’s define the two main sides of SEO.

On-Page SEO refers to everything that happens within the website itself such as HTML structure, site speed, responsiveness, accessibility, schema markup, meta tags, and more. Developers have a major impact here. If these foundations are weak, even the best content won’t perform well.

Off-Page SEO involves things like backlinks, content promotion, digital PR, and brand mentions. These activities are usually handled by the client or a dedicated SEO company. They help improve authority and trust, but they rely on a technically sound website to work effectively.

Developers aren’t expected to manage off-page SEO. But by focusing on the on-page basics, you make sure the site is ready to benefit from future marketing and growth efforts.

1. Use Semantic HTML for Clear Structure

Search engines don’t “see” your pages the way humans do—they interpret the HTML structure to understand what each part of a page represents. That’s where semantic HTML comes in.

Semantic tags give meaning to your content. Instead of using generic <div>s for everything, tags like <header>, <main>, <section>, <article>, and <footer> tell search engines and assistive technologies what role each block of content plays on the page.

For example:

<article>
<h2>Top 5 Benefits of Using No-Code Tools</h2>
<p>No-code tools allow faster MVP development...</p>
</article>

Using <article> instead of just a <div> signals that this is a standalone piece of content, which could be useful for indexing and for screen readers navigating by landmarks.

Heading hierarchy is just as important. Always use a single <h1> per page—usually for the main title—and follow with logically nested headings (<h2>, <h3>, and so on). This helps both accessibility tools and crawlers parse your content properly.

Avoid deprecated tags like <center>, <font>, <b>, and <i>. Instead, use modern alternatives like CSS for styling and <strong> or <em> for emphasis where the meaning matters.

If you're unsure about best practices or want a reference, Mozilla’s developer documentation is one of the most reliable sources.

2. Optimize Page Load Speed

Page speed has a direct impact on both search engine rankings and user behavior. In 2025, this isn’t just a “nice to have”—Google has made speed part of its ranking algorithm, and real users won’t wait more than a few seconds for a page to load.

As a developer, you have direct control over many of the elements that influence load time. Here's what to focus on:

Image Optimization

Images are often the heaviest assets on a site. Compress them using tools like Squoosh or TinyPNG before uploading. Use modern formats like WebP or AVIF, which maintain quality at smaller file sizes. Also, apply loading="lazy" to defer off-screen images and reduce initial load time.

Code Minification and Bundling

Minify your CSS and JavaScript files to reduce their size. Tools like Terser and cssnano can automate this process. Also, remove unused code—don’t ship unnecessary scripts from third-party libraries you’re not actually using.

Reduce Render-Blocking Resources

CSS and JavaScript files that block the browser from rendering the page should be deferred or async-loaded when possible. Inline critical CSS and defer the rest. Split large JS bundles using dynamic imports.

Caching and CDN

Use browser caching headers to reduce load time on repeat visits. And always serve static assets via a Content Delivery Network (CDN), like Cloudflare or Netlify Edge, to ensure fast delivery based on user location.

Fonts

Self-host fonts or use font-display: swap; to prevent invisible text delays. External font providers can block rendering if not loaded properly.

To measure and track improvements, use:

• Google PageSpeed Insights

• Lighthouse

• WebPageTest

Each of these tools breaks down performance issues and gives prioritized suggestions based on real browser conditions.

3. Ensure the Site is Crawlable and Indexable

If search engines can’t access the website’s content, they can’t rank it. It’s that simple.

Crawlability and indexability are the foundations of any SEO strategy. As a developer, your job is to make sure that nothing in the code or configuration blocks search engines from understanding what’s on the page.

Here’s what that means in practice:

robots.txt File

This file tells search engines which parts of the site they’re allowed to crawl. A misconfigured robots.txt can block important content unintentionally. For example:

User-agent: *
Disallow: /admin/
Allow: /

Make sure you're not accidentally disallowing key directories like /blog/ or even the entire site.

Learn more here: Google’s robots.txt documentation

Sitemap.xml

Every website should have an up-to-date XML sitemap that lists all the indexable pages. This file helps Google and other engines discover new content faster, especially if your internal linking isn’t perfect.

Use tools or plugins (depending on your stack) to generate and auto-update your sitemap. Don’t forget to submit it in Google Search Console.

Reference: Build and submit a sitemap

JavaScript Rendering Issues

If you're using JavaScript frameworks like React, Vue, or Angular, remember that search engines don’t always execute JavaScript the way browsers do. If your content is loaded dynamically, it may not be indexed at all.

To avoid this:

• Use server-side rendering (SSR) or static site generation (SSG)

• Include important content in the initial HTML

• Test using Google’s tools

Test how Googlebot sees your page: URL Inspection Tool

Canonical Tags

Use <link rel="canonical"> to tell search engines which version of a page is the “main” one. This helps prevent duplicate content issues, especially on e-commerce or filterable content.

4. Build for Mobile-First Experience

Google now uses mobile-first indexing by default. This means the mobile version of your site is what gets evaluated for ranking—not the desktop one. So if your desktop version looks polished but your mobile experience is slow, cluttered, or broken, it’s your mobile code that will get indexed—and ranked accordingly.

As a developer, building mobile-first isn't just about using media queries. It's about structuring your site so that it performs well, loads fast, and works smoothly on smaller screens from the ground up.

Here’s what to focus on:

Responsive Layouts

Use flexible grid systems, relative units like em, rem, and %, and media queries to adapt your layout across screen sizes. Avoid fixed-width containers. Prioritize vertical stacking and simplify your design when screen real estate is limited.

Touch-Friendly UI

Mobile users interact differently. Buttons and links should be large enough to tap without zooming (at least 48x48px), and elements shouldn’t be too close together. Avoid hover-only interactions—they don’t work well on mobile.

Readable Text and Scalable Fonts

Ensure your font sizes are legible without pinching or zooming. Stick to a base font size of at least 16px and avoid ultra-thin font weights. Use viewport units or relative sizing to maintain consistency across devices.

Optimized Mobile Performance

Mobile users are often on slower connections. Compress resources, avoid large JS bundles, and minimize third-party scripts. Lazy-load off-screen images and prioritize core content first.

Test Across Devices

Don’t assume responsiveness means it works everywhere. Use tools like:

• Chrome DevTools Device Mode
• Google’s Mobile-Friendly Test

These tools let you simulate mobile devices, test responsiveness, and see how search engines view your mobile experience.

Why This Matters for SEO

If the mobile version of your site is broken or missing key content, that’s the version Google will index—meaning poor mobile execution will hurt your visibility. And since over 60% of users now browse from their phones,

5. Implement Structured Data (Schema Markup)

Structured data is one of the most overlooked but powerful tools in technical SEO. It allows you to add context to the content on your website, making it easier for search engines like Google to understand what your page is about—and in many cases, enhance how it appears in search results.

When properly implemented, structured data can enable rich results, like star ratings, pricing details, FAQ dropdowns, event dates, breadcrumbs, and more. These visual enhancements help your pages stand out in the SERPs, which can lead to higher click-through rates.

The most common way to implement structured data is using JSON-LD, a JavaScript-based format recommended by Google. One simple example is the FAQ schema, which adds a list of questions and answers that can appear directly under your page result:

{
  "@context": "https://schema.org",
  "@type": "FAQPage",
  "mainEntity": [
    {
      "@type": "Question",
      "name": "How does structured data help SEO?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It provides additional context to search engines, which can lead to enhanced search appearances like rich results."
      }
    },
    {
      "@type": "Question",
      "name": "What format should I use for structured data?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Google recommends using JSON-LD for adding structured data to your pages."
      }
    }
  ]
}

Google's official documentation on structured data provides a full list of supported schema types and best practices for implementation. You can also use their Rich Results Test to validate your markup and see which types of enhancements your page may qualify for.

For developers, understanding how and where to use structured data is becoming part of the standard skillset—especially for content-heavy websites, blogs, product pages, and any site that could benefit from extra visibility in search.

Make sure structured data is part of your build process, not just an afterthought. It takes very little time to implement but adds a lot of value to the overall SEO foundation.

6. Set Accurate Meta Tags

Meta tags are essential for how your pages are interpreted and displayed by search engines and social media platforms. Even though they’re not visible on the page itself, they influence everything from rankings to click-through rates and link previews.

As a developer, your responsibility is to ensure that each page includes the correct meta structure, and that those tags are unique, accurate, and properly formatted across the site.

Here are the key meta tags to pay attention to:

Title Tag

The <title> tag defines the main title of a page shown in search results and browser tabs. It's one of the most important elements for SEO.

• Every page should have a unique title
• Keep it concise and aligned with the page content

Learn more: Google Title Links Documentation

Meta Description

The <meta name="description"> tag provides a short summary of the page’s content for search engines. It doesn’t affect rankings directly, but it strongly influences click-through rates in search.

• Write clear, relevant descriptions
• Avoid duplicating descriptions across pages

Learn more: Google Meta Description Guidelines

Open Graph and Twitter Metadata

Social platforms use Open Graph and Twitter Card tags to generate previews when a page is shared. While not part of SEO rankings, they impact how clickable your content appears across networks.

• Define custom previews for Facebook, LinkedIn, and X (Twitter)
• Include metadata for title, description, image, and URL

Resources:

• Open Graph Protocol
• Twitter Card Markup Guide

Avoiding Duplicates and Conflicts

Pages built dynamically through CMSs or JavaScript frameworks often inherit duplicate meta tags if not managed properly. Duplicates can confuse search engines and reduce the clarity of your pages in SERPs.

Make sure that:

• Meta tags are dynamically rendered when using SPAs
• Each URL renders unique metadata

Accurate meta tags help search engines and users understand your content before they even visit the site. They're a core part of SEO foundations and should always be handled with the same attention as other key technical elements.

7. Handle JavaScript with SEO in Mind

7. Handle JavaScript with SEO in Mind

Modern websites often rely on JavaScript frameworks like React, Vue, or Angular to power dynamic interfaces. But while these tools improve interactivity, they also introduce SEO challenges—especially when critical content is rendered client-side.

Search engines can technically crawl JavaScript, but it’s not always guaranteed or consistent. If key content isn’t available in the initial HTML, there's a risk it won’t be indexed at all.

As a developer, your job is to make sure that important SEO-related content (like headings, links, and body text) is accessible to search engines without relying on full client-side rendering.

Understand How Search Engines Render JS

Google uses a two-stage process to index JavaScript content: crawling the page, then rendering it using a headless browser. This can delay indexing and sometimes fail entirely if scripts don’t load correctly.

Learn more: Google’s JavaScript SEO Basics

Use SSR or SSG When Possible

Frameworks like Next.js, Nuxt, and SvelteKit offer server-side rendering (SSR) and static site generation (SSG), which allow pages to be delivered with full HTML content upfront—making it easier for search engines to index.

Reference: Google’s advice on dynamic rendering

Test How Google Sees Your JS Pages

Use Google Search Console’s URL Inspection Tool to check if your JavaScript-powered content is being rendered and indexed properly.

Tool: Google Search Console – URL Inspection

Don’t Block JS or Resources in robots.txt

Make sure your robots.txt file doesn’t block scripts or resources that are needed for rendering. Googlebot needs access to JS, CSS, and API responses to properly evaluate the page.

Guide: Robots.txt Best Practices

JavaScript and SEO can work together—if implemented correctly. By understanding how rendering affects indexing and using modern techniques like SSR or pre-rendering, you ensure your site stays both dynamic and discoverable.

9. Improve Accessibility for All Users

Accessibility is not just a moral imperative; it's a strategic advantage. By designing websites that are accessible to all users, including those with disabilities, you enhance the user experience for everyone. Accessible websites are often more navigable, faster, and easier to understand, which benefits all users regardless of their abilities. Moreover, accessibility aligns closely with SEO best practices, as search engines favor websites that are user-friendly and well-structured.​

Implementing accessibility features can also lead to tangible improvements in website performance. A study analyzing over 800 websites found that after implementing accessibility solutions, 73.4% experienced an increase in organic traffic, with an average overall traffic increase of 12%. These enhancements not only make your site more inclusive but also expand your reach to a broader audience, including the 1.3 billion people worldwide living with some form of disability.​

To ensure your website meets accessibility standards, refer to the Web Content Accessibility Guidelines (WCAG) provided by the World Wide Web Consortium (W3C). These guidelines offer comprehensive recommendations for making web content more accessible.

10. Monitor Core Web Vitals

9. Optimize for Core Web Vitals

Core Web Vitals are a set of performance metrics introduced by Google that reflect how users experience your website. They focus on three key areas: loading performance (Largest Contentful Paint or LCP), interactivity (Interaction to Next Paint or INP), and visual stability (Cumulative Layout Shift or CLS). These metrics help developers understand whether their site feels fast and responsive to real users. Google has made Core Web Vitals part of its ranking system, meaning they’re not just UX metrics—they now influence SEO as well.
Learn more: Google’s Core Web Vitals documentation

Although content quality is still the primary factor in ranking, Core Web Vitals often act as a tiebreaker between similarly relevant pages. According to a report by Vercel, Google relies on field data collected from Chrome users to evaluate these metrics, which can directly affect your position in the search results. Sites that perform well on these signals tend to have lower bounce rates, longer visit durations, and higher engagement.
Reference: How Core Web Vitals Affect SEO – Vercel

To monitor and improve Core Web Vitals, developers can use tools like Google Search Console, PageSpeed Insights, and Lighthouse. These tools offer both lab and field data, helping you identify bottlenecks and prioritize fixes. Optimizing for Core Web Vitals not only supports better SEO—it improves user satisfaction, reduces frustration, and strengthens the overall credibility of the website.

Final Thoughts

You won’t always find SEO listed in the scope of a development project. But thinking about it from the start—and building with it in mind—can make a real difference.

A well-structured, fast, and accessible site doesn’t just help your client. It reflects the level of care and quality you bring to your work. And when you consistently go a step beyond what’s expected, you become the kind of developer clients want to work with again and again.

Treat SEO as part of your craft. Understand the basics, apply them with purpose, and you’ll not only improve the websites you build—you’ll grow your own skill set in the process. That’s how you stand out. That’s how you level up.