Technical Information
| HTTP Status Code | 521 |
| HTTP Version | HTTP/1.1 |
| HTTPS | ✔ Available |
| IP Address | 104.21.14.117 |
| Server Software | cloudflare |
| CDN | Cloudflare |
|
ℹ 🔵 Missing HSTS | HTTP Strict Transport Security is not configured. Recommended for HTTPS sites. |
|
ℹ 🔵 Missing Content Security Policy | CSP is not configured. It helps prevent XSS attacks and content injection. |
HTTP Status Code 521
HTTP Version HTTP/1.1
HTTPS ✔ Available
IP Address 104.21.14.117
Server Software cloudflare
CDN Cloudflare
ℹ 🔵 Missing HSTS HTTP Strict Transport Security is not configured. Recommended for HTTPS sites.
ℹ 🔵 Missing Content Security Policy CSP is not configured. It helps prevent XSS attacks and content injection.
Performance
| DNS Lookup | 11.1 ms |
| TCP Connect | 13 ms |
| TLS Handshake | 7.8 ms |
| Time To First Byte (TTFB) | 215 ms |
| Content Download | 0.1 ms |
| Total Response Time | 215.1 ms |
DNS Lookup 11.1 ms
TCP Connect 13 ms
TLS Handshake 7.8 ms
Time To First Byte (TTFB) 215 ms
Content Download 0.1 ms
Total Response Time 215.1 ms
Security
| HTTPS | ✔ Enabled |
| HSTS | ✘ Not configured |
| CSP | ⚠ Not configured |
| X-Frame-Options | ✔ SAMEORIGIN |
| X-Content-Type-Options | ⚠ Not configured |
| Referrer Policy | same-origin |
| HTTP/2 | ⚠ HTTP/1.1 |
HTTPS ✔ Enabled
HSTS ✘ Not configured
CSP ⚠ Not configured
X-Frame-Options ✔ SAMEORIGIN
X-Content-Type-Options ⚠ Not configured
Referrer Policy same-origin
HTTP/2 ⚠ HTTP/1.1
SEO Quick Check
| Title | 21990.com | 521: Web server is down |
| Robots Meta | noindex, nofollow |
Title 21990.com | 521: Web server is down
Robots Meta noindex, nofollow
Detected Technologies
| Technology | Google Analytics Cloudflare |
Technology Google Analytics Cloudflare
HTTP Headers
| Date | Thu, 20 Aug 2026 00:41:01 GMT |
| Content-type | text/html; charset=UTF-8 |
| Content-length | 6979 |
| Retry-after | 120 |
| Cache-control | private, max-age=0, no-store, no-cache, must-revalidate, post-check=0, pre-check=0 |
| Expires | Thu, 01 Jan 1970 00:00:01 GMT |
| Referrer-policy | same-origin |
| X-frame-options | SAMEORIGIN |
| Server | cloudflare |
| Cf-ray | a2dd5995bc06d0aa-CDG |
| Alt-svc | h3=":443"; ma=86400 |
Meta Tags
| Content-Type | text/html; charset=UTF-8 |
| X-UA-Compatible | IE=Edge |
| Robots | noindex, nofollow |
| Viewport | width=device-width,initial-scale=1 |
Date Thu, 20 Aug 2026 00:41:01 GMT
Content-type text/html; charset=UTF-8
Content-length 6979
Retry-after 120
Cache-control private, max-age=0, no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Expires Thu, 01 Jan 1970 00:00:01 GMT
Referrer-policy same-origin
X-frame-options SAMEORIGIN
Server cloudflare
Cf-ray a2dd5995bc06d0aa-CDG
Alt-svc h3=":443"; ma=86400
