Services

Next.js Performance and Stability Debugging

When the platform is already live, the pain usually shows up as slow routes, brittle rendering, or regressions nobody has isolated confidently.

Debug live Next.js stacks that became slower, less stable, or harder to reason about after a release, redesign, dependency change, or script rollout.

Short Answer

Something has changed, and the Next.js site no longer behaves reliably under live conditions. Performance and stability issues often sit between routing, caching, rendering strategy, scripts, data fetching, deployment behaviour, and release process. I narrow the work to the first real constraint and fix it without turning a live platform into a rewrite.

Why It Matters

For product and delivery leaders, the priority is stopping more changes from compounding the regression. I isolate live‑stack constraints that are affecting conversion, platform stability, and release confidence.

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, image weight, data fetching, or caching behaviour.

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

What I Look at First

I usually start by checking the affected templates, Core Web Vitals data, rendering path, image and font behaviour, third‑party scripts, caching, data loading, deployment history, and whether the issue is reproducible in production.

What Usually Changes

  1. Live regressions are tied to routes, templates, runtime behaviour, scripts, images, data loading, or cache paths.

  2. The first real bottleneck is separated from score noise and secondary symptoms.

  3. Fixes are prioritised by user journey, commercial exposure, and release complexity.

  4. The team has a verification path for field data, lab checks, and production behaviour.

  5. Release confidence improves because the cause and the fix route are both clear.

How This Usually Works

  1. Technical Diagnostic

    A focused review of affected routes, templates, deployment behaviour, crawl signals, CMS behaviour, performance bottlenecks, or code paths, followed by a prioritised fix plan the team can take into delivery.

  2. Recovery Sprint

    A short, concentrated engagement for a defined technical SEO, performance, CMS, Vercel, migration, or production issue where the business needs the cause isolated and the first fixes moved quickly.

  3. Embedded Delivery Support

    Senior hands‑on support inside an existing team where architecture, implementation, review, and delivery judgement all matter, especially when the work cannot be handed over as isolated tickets.

This May Not Be the Right Fit If

  • You only need a score‑chasing exercise, a one‑off Lighthouse export, or cosmetic advice without implementation authority. If a measurable regression needs engineering diagnosis, Next.js Core Web Vitals Regression Fix is the better starting point.
  • The business is not ready to prioritise routes, templates, scripts, and release changes by real user and commercial impact. If the immediate pressure is script weight or tag behaviour, Third‑Party Script Performance Optimisation may be the more focused route.

Talk to me about your performance problem

A short description of the affected route, metric, or recent release is enough. I'll read it and suggest the next step.

Get in touch

Related Project Work

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

    A New User Experience and Features for Selfridges

    At Selfridges, e‑commerce front‑end work had to keep perceived speed, release quality, and commercial flows stable under pressure.

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

    The Optimisation and Rebrand of johnlewis.com

    On John Lewis, Core Web Vitals and front‑end optimisation work on high‑traffic retail pages left little room for regressions in speed, stability, or search visibility.

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

    A Complete Migration and Replatform for Nando’s

    On Nando’s restaurant pages, speed, structured data, and local discovery were handled as one customer path rather than separate score‑chasing exercises.

    View project

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