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WEB PERFORMANCE

PSI Performance 95+.
Guaranteed and documented.

The guarantee covers the PageSpeed Insights Performance score at delivery, for the pages and conditions defined in the quotation. Field data is measured separately.

Assess my website Explore the improvements
A dial illustrating technical performance.
An illustration, not a measured score. Editorial illustration.

Performance optimisation starts with measurement, identifies the actual bottleneck and validates each change under comparable conditions. Lighthouse and PageSpeed Insights support diagnosis; field Core Web Vitals describe real experience when sufficient data is available. Also read the LCP, INP and CLS guide.

≤ 2.5 s
Good LCP
Google threshold at the 75th percentile
≤ 0,1
Good CLS
Google threshold at the 75th percentile
≤ 200 ms
Good INP
Google threshold at the 75th percentile
95+
PSI Performance
Guaranteed at delivery under the protocol
INTERACTIVE TOOL

Performance self-assessment
in 30 seconds.

Tick the criteria already in place. We calculate your self-assessed score and identify priority improvements.

My current criteria:

Self-assessed score

0
/100

Tick your criteria to see your score.

This checklist indicates which practices are in place. It does not predict a Lighthouse score or field data.

Complete professional audit

Indicative self-assessment. Then measure Lighthouse under repeatable conditions and field Core Web Vitals where available.

Core Web Vitals

The 3 metrics recommended by Google.

Field thresholds are assessed at the 75th percentile. They contribute to page experience without guaranteeing a ranking.

The visual guide

What your visitor experiences behind the metrics

Real experience

  • See the content

    LCP tracks when the largest visible element appears.

  • Keep your bearings

    CLS describes unexpected page shifts.

  • Get a response

    INP describes responsiveness after an interaction.

Field data and lab tests remain two distinct perspectives.

LCP

Largest Contentful Paint

Time until the largest visible element is displayed.

Good: ≤ 2.5 s Poor: > 4 s

CLS

Cumulative Layout Shift

Visual stability during loading and use.

Good: ≤ 0.1 Poor: > 0.25

INP

Interaction to Next Paint

Responsiveness between a user action and the next visual update.

Good: ≤ 200 ms Poor: > 500 ms
Improvements

6 major technical improvements.

High-impact optimisations we apply across our projects.

01

Image optimisation (WebP/AVIF)

Automatic conversion, responsive sizes and native lazy loading.

02

CDN + aggressive caching

Cloudflare with fine-grained cache rules, immutable assets and Brotli.

03

Optimised JavaScript

Code splitting, tree shaking, defer/async and jQuery removal.

04

Inline critical CSS

Above-the-fold critical CSS inline, with the rest loaded asynchronously.

05

Self-hosted fonts

Subset WOFF2, font-display: swap and preloading of critical fonts.

06

Rendering suited to the project

Pre-rendering, server-side or client-side rendering selected according to content and interactions.

Method

4 steps, with measurement at every stage.

  1. 01

    Lighthouse + WebPageTest audit

    Mobile + desktop baseline measurement and bottleneck identification.

    Day 1

  2. 02

    Prioritised optimisation plan

    Quick wins (images, caching), then structural work (CSS, JS, SSR).

    Days 2-3

  3. 03

    Implementation

    One optimisation at a time, measuring the impact at every step.

    Weeks 1-3

  4. 04

    Validation + monitoring

    Check of the PSI 95+ guarantee under the agreed protocol, followed by field data where available.

    Ongoing

Transparency

What is included,
and what is not.

Included in the price

  • Mobile + desktop Lighthouse and WebPageTest audit
  • Prioritised optimisation plan: quick wins + structural work
  • WebP/AVIF image conversion + lazy loading
  • Cloudflare CDN configuration + aggressive caching + Brotli
  • JavaScript optimisation (code splitting, defer)
  • Inline critical CSS + asynchronous non-critical CSS
  • Self-hosted subset WOFF2 fonts
  • PSI Performance score of 95+ guaranteed at delivery under the agreed protocol
  • Before-and-after measurements under a documented protocol
  • RUM monitoring for 30 days after delivery
  • Documentation of the optimisations applied

Optional or available separately

  • Visual redesign (separate service)
  • Framework migration (WordPress → Astro, on quotation)
  • Bulk optimisation of more than 500 existing images (optional extra)
  • Performance maintenance after day 30 (optional package)
Investment

Three performance packages.

Express audit

One-off assessment and action plan

950 €
Excluding VAT · Audit + 90-day plan
  • Complete Lighthouse audit
  • WebPageTest waterfall
  • Prioritised optimisation plan
  • 1-hour presentation of findings
  • No implementation
Most requested

Optimisation Sprint

Existing website with identified priorities

€3,500 to €6,500
Excluding VAT · Audit + implementation
  • Audit + plan + implementation
  • Quick wins + structural optimisations
  • PSI Performance 95+ guaranteed under the protocol
  • 30 days of RUM monitoring where available
  • Documentation

Continuous Performance

Website to monitor over time

From €850/month
Excluding VAT · Commitment of 6+ months
  • RUM monitoring where available
  • Regression alerts
  • In-depth quarterly audit
  • Corrective optimisations included
  • Monthly reporting

Prices excluding VAT. Belgian VAT of 21% applies.

Frequently asked questions

All about web performance.

What does the PSI Performance 95+ guarantee cover?
Kanexio guarantees a PageSpeed Insights Performance score of 95 or above at delivery for the pages, version, device type and testing protocol specified in the quotation. Validation is dated and documented. This commercial guarantee does not cover CrUX field data, Google rankings, conversions or subsequent changes made by the client or a third party.
How much does performance optimisation cost in Brussels?
The packages shown cover auditing, implementation or ongoing monitoring. The final scope depends on the stack, number of templates and third-party scripts. No generic ROI or payback period is promised.
What is the difference between Lighthouse and Core Web Vitals?
Lighthouse simulates a visit and provides several lab audits. The Core Web Vitals LCP, CLS and INP can be measured in the field, including through the Chrome UX Report, at the 75th percentile. A website can therefore show different results depending on the tool, period and audience. Read our Core Web Vitals guide.
How long does it take to improve performance?
That depends on the actual bottleneck: images, server, theme, third-party scripts, JavaScript or architecture. The audit establishes a baseline, then each change is measured. No point increase or timeframe is confirmed before this analysis.
Can performance optimisation break my website?
Every change carries a risk. A test environment, backups, visual and functional checks, versioned changes and a rollback plan reduce it. Apreliminary audit helps select proportionate interventions.
Why consider self-hosting fonts?
Self-hosting can reduce a third-party dependency and give more control over files, caching and subsets. The choice must also consider licences, the actual configuration and data protection obligations. It is not, on its own, evidence of compliance.
How can we maintain good performance over time?
Monitor field data where available, automate lab tests on stable pages and check new images, fonts and third-party tags. Ongoing maintenance can detect regressions without guaranteeing an unchanging score.

Web performance in Uccle and all municipalities: Ixelles, Saint-Gilles, Etterbeek, Woluwe-Saint-Pierre and 15 others.

Free performance audit.

30 minutes by video call: a live Lighthouse test of your website, bottleneck identification and a costed optimisation plan. No obligation.

Request the free audit View the case studies