Services

Next.js Performance and Stability Debugging

Start here when the platform is already live and the pain shows up as slow routes, brittle rendering, or regressions nobody has isolated confidently.

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

Common situations

  • Core Web Vitals regressions after a release, redesign, or third‑party change.
  • Hydration mismatches or unstable server and client rendering boundaries.
  • Slow pages caused by scripting overhead, images, or caching behaviour.

Choose the problem that most closely matches the current live‑stack behaviour.

Choose the closest scenario

  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 consulting support

  2. Capability

    Next.js Platform Consulting

    Bring in senior Next.js architecture support when a legacy platform, older front end, or hard‑to‑maintain site needs migration planning, platform rescue, and clearer delivery direction.

  3. Capability

    Technical SEO for JavaScript Applications

    Bring in engineering‑led SEO help when Google is not indexing important JavaScript pages because rendering, crawlability, metadata, or migration changes are getting in the way.

  4. Capability

    Headless Architecture Consulting

    Bring in headless CMS consulting when CMS architecture, SEO controls, preview trust, or revalidation decisions are about to lock in operational pain.

Related project experience

  1. 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.

  2. 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.

  3. 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.

  4. Linkudo

    Freelance full‑stack developer for this modern reimagining of the classic browser‑based word association game. Built with Next.js, Node.js, Supabase, and Redis.

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

Supporting technical articles

Tell me what needs fixing

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.

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