sommenoefenen.nl

Readiness by lane

Green: sommenoefenen.nl. Thin bar: Education & Online Learning peer median.

Priority fixes for sommenoefenen.nl

Ordered by impact and by how common each practice is among peers.

1. Priority 1 · Harden

   HSTS kept for at least a year

   Observed: Strict-Transport-Security was sent with a max-age of 183 days, below the one-year benchmark.

   Why it matters: HSTS tells browsers to use HTTPS for your host on every later visit, which removes the window where a first HTTP request can be intercepted.

   What to do: Send Strict-Transport-Security on HTTPS responses. Start with a short max-age (for example 300 seconds), confirm every subdomain works over HTTPS, then raise it in steps to 31536000. Add includeSubDomains only when all subdomains are HTTPS. HSTS preload is optional and hard to undo; hstspreload.org itself does not recommend it by default.

   34% of Education & Online Learning peers do this. Limit: Read from the homepage response only; other pages or regions may send different headers.

   Guide: HTTPS and TLS Guide for Website Owners

2. Priority 2 · Enable

   XML sitemap discoverable

   Observed: No sitemap was listed in robots.txt or found at /sitemap.xml.

   What to do: Generate an XML sitemap of canonical URLs, reference it in robots.txt and submit it in Google Search Console.

   65% of Education & Online Learning peers do this.

   Guide: XML Sitemap Guide: Include Only URLs You Stand Behind

3. Priority 3 · Harden

   DMARC policy enforces quarantine or reject

   Observed: No DMARC record was found at _dmarc.sommenoefenen.nl.

   What to do: Publish DMARC with p=none and a reporting address first, fix any legitimate senders that fail SPF or DKIM alignment, then move to quarantine and finally reject.

   36% of Education & Online Learning peers do this.

   Guide: A Practical Website Health Check for Owners

4. Priority 4 · Accelerate

   Modern image formats in use

   Observed: The homepage had 15 images and none used WebP or AVIF.

   What to do: Serve WebP or AVIF with a JPEG or PNG fallback, either through an image CDN or by generating both formats at build time.

   32% of Education & Online Learning peers do this.

   Guide: AVIF, WebP, JPEG, and PNG: Choose the Right Image Format

What sommenoefenen.nl already does well

Practices fewer than half of Education & Online Learning peers use.

• DNSSEC signedDNSSEC delegation (DS record) present.8.1% of peers
• Nameservers spread across providersNameservers spread across more than one operator.13% of peers
• Reachable over IPv6IPv6 address published.39% of peers

What we saw

Homepage checked

https://www.sommenoefenen.nl/

Homepage response

HTTP 200

TLS

TLSv1.3, HTTP/2

Certificate

Trust Provider B.V., 198-day validity, expiring 2026-12-12

DNS operators

2 self-run or other nameserver domains

HSTS

max-age 183 days

Homepage HTML

15 KB, gzip

Images on homepage

15 (png 13, jpg 2)

Limits: homepage only, one location, one moment. Header checks reflect the homepage response; other pages may differ.

All 31 checks

Select a gap for the method and fix. How each check works

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Education & Online Learning readiness benchmark