JavaScript SEO.
Rendering audits for React, Next.js, Vue and headless websites.
SEMANTIKOS checks whether the content, links and tags on a JavaScript website reach search engines and AI systems intact. Each audit compares the initial HTML response with the rendered page, then sets out prioritised fixes for the development team.
- Server-side rendering
- Hydration
- Frameworks
- Script loading
- Page weight
Search engines read pages in two passes.
Crawlers first fetch the HTML a server returns. Rendering the JavaScript comes later, in a separate queue, and can be delayed or incomplete. Anything that only exists after scripts run is at risk of being seen late or not at all.
AI crawlers add a further consideration, because many of them fetch the HTML without running scripts. For those systems, content that depends on client-side rendering is effectively missing.
Performance tooling can widen the gap. Script deferral features, lazy-loading plugins and caching layers are often added to improve speed scores, and each one changes when and how page elements appear.
JavaScript SEO services
Rendering comparison
Side-by-side analysis of raw HTML and rendered output for each page template, listing every link, heading, tag and block of content that differs.
Framework configuration
Reviewing server-side rendering, static generation and hydration settings in Next.js, Nuxt, React and similar frameworks.
Script loading review
Checking that deferral, lazy-loading and CDN optimisation features do not delay or rewrite elements search engines rely on.
Canonical and metadata stability
Confirming that canonical tags, titles, robots rules and structured data are present in the initial HTML and stay unchanged after rendering.
Internal link discovery
Making sure navigation and product or listing links are standard anchor elements that crawlers can follow without interaction.
Page weight and DOM size
Measuring inline styles, script bundles and image configuration that inflate the HTML and slow both parsing and rendering.
AI crawler accessibility
Testing how pages appear to crawlers that do not execute JavaScript, and which facts need to be present in the server response.
Core Web Vitals
Linking loading, layout stability and responsiveness issues to the templates and scripts that cause them.
A template-by-template audit.
Template sampling
Selecting representative URLs for every page type, from the homepage to deep product, article or listing pages.
Dual capture
Recording the initial HTML and the rendered page for each sample, on desktop and mobile.
Difference analysis
Listing what is missing, delayed or altered between the two versions, and estimating how many URLs each issue affects.
Engineering requirements
Writing fixes in terms of framework settings, component changes and configuration, with acceptance tests for each.
Release checks
Re-running the comparison after deployment and monitoring indexation of the affected templates.
What a rendering audit can look like.
Client work stays confidential. This scenario combines patterns common on framework-based marketplaces.
A Next.js marketplace behind an extra script loader
A marketplace built on Next.js adds a CDN feature that defers scripts to improve its speed score. Soon after, new listing pages take far longer to appear in search results.
The rendering comparison shows the framework scripts being held back by the deferral feature, so parts of the page depend on a second script running first. The HTML also carries a large volume of inline style blocks, and image settings generate many unnecessary size variants for small thumbnails.
The plan removes the redundant deferral layer and relies on the framework’s own script handling, moves styles into cached stylesheets and trims the image configuration. Work like this usually reduces page weight noticeably and gives crawlers a complete page on the first request.
This is a composite example based on patterns common to this kind of engagement. It does not describe a specific client.
When a JavaScript site needs an audit.
- The site was rebuilt on a JavaScript framework and organic traffic fell.
- Content or links appear in the browser but not in the page source.
- New pages take weeks to be indexed.
- A speed plugin or CDN optimisation feature was recently enabled.
- AI assistants cannot describe products or services accurately.
- Page source is dominated by inline styles and scripts.
Frequently asked questions
Can Google index JavaScript websites?
Yes, Google renders JavaScript, but rendering happens after crawling and uses more resources. Content in the initial HTML is indexed more reliably and more quickly.
Is server-side rendering necessary for SEO?
For most content-driven and commercial pages it is the safest option. Static generation and hybrid rendering also work well when configured correctly.
Do speed optimisation plugins hurt SEO?
They can when they defer or rewrite the scripts that build the page. The effect is visible by comparing raw HTML with the rendered result.
Do AI crawlers run JavaScript?
Many do not. Facts that matter for AI search visibility are best delivered in the server response.
Does SEMANTIKOS change the code?
SEMANTIKOS specifies the changes and reviews them. Implementation is usually handled by the client’s developers.