Services

Performance Optimisation and Core Web Vitals for Modern Web Platforms

Bring me in when the site feels slower after changes, harder to ship, or too expensive to keep tuning one regression at a time.

Bring in performance help when page loads feel slow, Core Web Vitals are slipping, or scripting cost is hurting key user journeys.

Where this fits

  • Core Web Vitals diagnostics across release, redesign, and migration work.
  • JavaScript, image, and caching changes that improve real user performance.
  • Performance reviews for live Next.js and modern front‑end stacks.

Common engagements

  • Short regression investigations after a launch or release.
  • Broader performance audits and remediation planning.
  • Implementation support for higher‑priority fixes.

Related hubs

  1. Hub

    Next.js Performance and Stability

    Choose the right performance and stability investigation when a live Next.js stack is slower, less stable, or harder to reason about after change.

Related scenarios

  1. Scenario

    Next.js Core Web Vitals Regression Fix

    Recover lost Core Web Vitals after a release before the site feels slower and key routes start hurting conversion, crawl efficiency, or release confidence.

  2. Scenario

    Next.js Hydration Mismatch Fix

    Diagnose hydration mismatches before Hydration failed errors, brittle UI, and production‑only rendering bugs start compounding.

Related project experience

  1. BBC
    Future Media

    The sole UI developer for the award‑winning fourth major version of the British Broadcasting Corporation homepage and the first step in a thorough new online identity and look and feel.

    Screenshot of the BBC Future Media website; part of John Kavanagh's development portfolio.

  2. Bose

    A lean, fast, highly accessible product support portal that allows users to self‑support rather than calling customer services. Provides easy‑to‑access manuals, videos, guides, and tips. Built with Mustache and AEM.

    Screenshot of the Bose Product Support website; part of John Kavanagh's development portfolio.

  3. Selfridges

    Lead front‑end developer within the e‑commerce Customer Experience team. Leading the delivery of new features, as well as considerable refactoring and improvement of the existing platform's performance.

    Screenshot of the Selfridges website; part of John Kavanagh's development portfolio.

  4. John Lewis
    & Partners

    Senior developer as part of team 'Findability'. Led the digital implementation of the 'John Lewis & Partners' rebrand alongside new feature development, user journey optimisation, and performance improvements.

    Screenshot of the John Lewis website; part of John Kavanagh's development portfolio.

  5. Nando’s

    Senior software engineer on the UK and Ireland replatform, migrating Nando’s customer‑facing websites from legacy Drupal to a unified headless platform built with Next.js and Storyblok, with a focus on performance, accessibility, and SEO.

    Screenshot of the Nando’s website; part of John Kavanagh's development portfolio.

  6. LEGO

    Senior developer producing an all‑new e‑commerce platform with React. Designed to handle high traffic volumes and support multi‑language and multiple currencies.

    Screenshot of the LEGO website; part of John Kavanagh's development portfolio.

  7. Plex.tv

    A complex, web‑based media library and player built in React that allows users to access their self‑hosted media from anywhere and on virtually any device with a web browser and an internet connection.

    Screenshot of the Plex.tv website; part of John Kavanagh's development portfolio.

Supporting technical articles

Also relevant

  1. Secondary service

    Accessibility and usability reviews

    Accessibility, assistive‑technology, and usability reviews for teams that need practical fixes rather than a compliance‑only report.

Send me the details

Send me the affected page or route, point me at the code if that helps, and tell me what you expected to happen versus what is happening now. If this connects to a Next.js migration, technical SEO drop, performance issue, launch, or platform move, include that context too. I'll come back with the clearest next step.

Send the details
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