o2.cz

Readiness by lane

Green: o2.cz. Thin bar: Telecommunications & Internet peer median.

Priority fixes for o2.cz

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

1. Priority 1 · Harden

   Certificate has more than 14 days left

   Observed: The certificate from DigiCert Inc was due to expire on 2026-10-29 (6 days after the check).

   Why it matters: An expired certificate makes browsers show a full-page warning. Renewing well ahead of expiry leaves time to fix a failed renewal.

   What to do: Automate renewal with ACME (for example Let's Encrypt or your CDN's managed certificates) and add a renewal review to your release calendar so any certificate inside 21 days of expiry gets attention.

   98% of Telecommunications & Internet peers do this. Limit: Certificate and protocol were observed from one vantage point; CDNs can present different certificates by region.

   Guide: HTTPS and TLS Guide for Website Owners

2. Priority 2 · Accelerate

   HTTP/2 negotiated

   Observed: The TLS handshake selected HTTP/1.1 instead of HTTP/2.

   What to do: Enable HTTP/2 on your CDN or server. Most CDNs do this by default.

   72% of Telecommunications & Internet peers do this.

   Guide: CDN Guide for Website Owners

3. Priority 3 · Harden

   HSTS kept for at least a year

   Observed: Strict-Transport-Security was sent with a max-age of 30 days, below the one-year benchmark.

   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.

   54% of Telecommunications & Internet peers do this.

   Guide: HTTPS and TLS Guide for Website Owners

4. Priority 4 · Accelerate

   Modern image formats in use

   Observed: The homepage had 27 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.

   52% of Telecommunications & Internet peers do this.

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

What o2.cz already does well

Practices fewer than half of Telecommunications & Internet peers use.

• DNSSEC signedDNSSEC delegation (DS record) present.13% of peers
• security.txt publishedsecurity.txt with a contact found.13% of peers
• Nameservers spread across providersNameservers spread across more than one operator.16% of peers

What we saw

Homepage checked

https://www.o2.cz/

Homepage response

HTTP 200

TLS

TLSv1.3

Certificate

DigiCert, 364-day validity, expiring 2026-10-29

DNS operators

2 self-run or other nameserver domains

HSTS

max-age 30 days

DMARC policy

p=quarantine

Homepage HTML

269 KB, gzip

Images on homepage

27

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

Stack and providers

Seen in the homepage response, certificate and DNS. Provider pages compare how their customers configure the same checks.

All 31 checks

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

Compare with other Telecommunications & Internet sites

• chatrwireless.com60
• smsbower.app60
• t-mobile.pl61
• tntph.com60
• vodafone.co.uk61

Telecommunications & Internet readiness benchmark