Sunweb is the main brand of the dutch tourist operator Sundio Group, offering summer destinations in Europe, mainly to Dutch customers. For the last fifteen years, they have been providing high quality package holidays at affordable prices. The website allows their customers to search for, get essential information and book their flight, accommodation and local transportation to destinations in the Mediterranean Sea.


Sundio Group is aware of the importance that web performance has in the business. They are already knowledgeable about best practices and tools, both server and client side, and they were looking for some expertise to consolidate their findings and provide guidance for further learning. They decided to contact us for a consulting project with an initial objective of measuring and optimizing the site, but without discarding other opportunities that could come up in the future regarding their other sites.


The actual works carried out for Sunweb have been very broad, the most relevant ones follow:

  • Establish a set of performance metrics for the site.
  • Introduce a performance tuning methodology that fits their current web development workflow.
  • Provide guidance on the tools and techniques for automating performance measurements.
  • Carry out performance measurements at given points in time, coinciding with the rollout of new releases.
  • Compare results with their main competitors and with global internet sites.
  • Analyze results and suggest improvements in their architecture, code or infrastructure.
  • Access their Google Analytics reports and make recommendations based on real user trends.
  • Use Sundio Group’s issue tracker based on Jira to document and follow up every action.

Among the optimizations that we have suggested for Sunweb we can highlight the following:

  • Fine tune their current cache policy for different resource types
  • Provide help in file revving strategies to make updates of cached files immediately visible
  • Proposal of different options and tools for image optimization and combination (sprites)
  • Proposal of several strategies for font loading, web font subsetting, icon font consolidation
  • Introduce the concept of the critical rendering path and the steps required to optimize it
  • Optimize the DOM in the initially served HTML document
  • Set up a Webpagetest private instance
  • Suggest optimization of the TCP initial congestion window

As an example, the following image shows the comparison of several key performance metrics with those of Alexa top 1M sites, for two releases (37 and 38) of the site: