Web development SEO is the set of technical decisions made during the build that decide how well a site can be crawled, rendered and ranked. They are made during web development and app development, and they have to survive whatever is added afterwards. A slow site, or one that hides its content from search engines, struggles to rank however good the copy is.
Why build decisions affect rankings
Search engines reward fast loads, quick responses to input, stable layouts and a clear structure, and all four are set in the templates. The same structure feeds AI answer engines, but most of their crawlers do not run JavaScript, so content an assistant can cite has to be in the HTML the server sends.
Core Web Vitals and page speed
Google’s targets for the three Core Web Vitals, at the 75th percentile of page loads, are a Largest Contentful Paint within 2.5 seconds, an Interaction to Next Paint of 200 milliseconds or less, and a Cumulative Layout Shift of 0.1 or less (web.dev, updated October 2024). INP replaced First Input Delay in 2024, so reporting that still shows FID is out of date.
The fundamentals, set out in how to build a high-performance website:
- Ship less JavaScript: remove unused libraries, or defer them past first paint.
- Optimise images: WebP or AVIF, sized per breakpoint, compressed, and lazy-loaded below the fold only.
- Cache aggressively: browser caching, server caching and a CDN.
- Use critical CSS: style the first screen inline so the page renders before the full stylesheet arrives.
- Reserve space for late-loading elements: a cookie banner or late hero that pushes the page down after paint is a common cause of a failing CLS score.
- Measure field data: lab tools such as Lighthouse show what is possible; field data shows what people get on a mid-range phone.
Agree a performance budget at the start of the project.
Crawlability, indexing and site architecture
Make sure search engines can discover and understand every page:
- Logical URL structure: predictable slugs and consistent patterns, decided before the first page is built.
- XML sitemap and robots.txt alignment: the sitemap lists exactly what you want indexed, and robots.txt blocks nothing the sitemap includes.
- Canonical tags: prevent duplicates from filters, sorting, tracking parameters and trailing-slash variants.
- Correct status codes: no soft 404s, no redirect chains, and 301s used deliberately when a URL moves.
- Structured data:
Organization,ArticleandFAQPagemarkup emitted by the templates.
Rankings are most often lost at a redesign, when a new site launches on new URLs and the old ones return 404. Put the redirect map from every old URL in the build scope. ESMA’s new site keeps 338 redirects from its old addresses (ESMA case study). The steps we ran when loco.ie moved are in how to redesign a website without losing rankings.
How do you stop JavaScript hiding your content from search engines?
React, Next.js, Vue and Nuxt are all fine choices, but SEO suffers when core content only appears after client-side rendering. Google queues rendering separately from crawling, and other search engines and AI crawlers are less patient.
- Prefer SSR or SSG for indexable pages: render content and metadata (title, description, canonical, Open Graph) on the server or at build time.
- Keep navigation, headings and body copy in the initial HTML.
- Handle pagination and filters deliberately: decide what should be indexed, and mark it up accordingly.
Can custom development be an SEO advantage?
Yes, done properly. Plugins and themes left on their defaults bring extra weight, untidy markup and limits on content structure. Custom development gives you lean templates and a content model where services, case studies and FAQs are types the team can extend. It does not have to mean a framework built from nothing; what matters is who controls the output. Palmer Shore launched in 2026 with no previous site, on a content model its own team extends. On Total Expo we built a component library and a CMS the team runs.
Accessibility and SEO overlap
Clear page structure, meaningful headings, descriptive link text, keyboard navigation and readable contrast make a site easier for search engines to parse and for people to use, and take friction out of the path to an enquiry.
If you sell to consumers online, the European Accessibility Act has applied since 28 June 2025 (micro-enterprises providing services are exempt), transposed in Ireland as S.I. No. 636/2023 and enforced for online shops and other ecommerce services by the CCPC. Build to WCAG 2.2 AA from the first component, which also satisfies 2.1; a plugin overlay will not get you there. Our guide to web accessibility laws in Ireland covers who is in scope, and a website accessibility audit shows where an existing site stands.
Treat content and internal linking as part of the build
Design the architecture around user journeys, then connect related pages with deliberate internal links.
A simple internal linking framework
- Service pages link to the most relevant case studies and supporting posts.
- Blog posts link back to the matching service page where it helps the reader.
- Case studies link to the services used and to related outcomes.
Use descriptive anchor text, and keep every page that matters within a few clicks of the home page. Orphaned pages rarely rank.
Make your website AI-ready without losing SEO fundamentals
Answer engines quote content that is structured, clear and trustworthy, and an assistant that cannot render your page will cite a competitor’s. The steps overlap with the rest of this list: server-rendered content, clean headings, question-form subheadings with direct answers, FAQ and Article schema, and a named author with a real job title. Our AI-ready website development service builds to that standard, and how to build an AI-ready website and answer engine optimisation cover the content side.
Web development best practices to ask about before you build
- How are SEO-critical pages rendered, and what happens with JavaScript disabled?
- Who owns the redirect map from every old URL, and when is it due?
- What are the LCP, INP and CLS targets, and who measures field data after launch?
- What is the plan for releases, monitoring and SEO-led improvements after launch?
If a supplier cannot answer these in the first conversation, ask again before you sign.
