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21tb.com

https://21tb.com· First analyzed 31 May 2026· Updated 31 May 2026
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21tb.com
Desktop screenshot of 21tb.com
Mobile screenshot of 21tb.com
Mobile

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Hosting Provider

ChinaNetCenter Ltd.

IP Address

123.103.18.6

Site Location

🇨🇳 Chinavia ip

Server Location

🇨🇳 Beijing, China

ASN

AS23724

Organization

ChinaNetCenter Ltd.

Server

F-WEB

Nameservers

ns1.21tb.com.ns2.21tb.com.ns3.21tb.com.

Performance

78

Core Web Vitals

Weight

First Contentful Paint
2.5 s10%
Speed Index
3.3 s10%
Largest Contentful Paint
—25%
Total Blocking Time
0.0 ms30%
Cumulative Layout Shift
0.00025%
65 KB
106 requests

Image Optimization

Lazy LoadWebP
0–49
50–89
90–100

Architecture Stack

Monolithic
⚙️ SSR
Infrastructure
Hosting
ChinaNetCenter Ltd.

Technology Stack

2 Technologies Detected

Libraries

1
jQuery

CSS Frameworks

1
Tailwind CSS

SEO Analysis

C60/100
16
8
1
Meta Tags12/15
Content8/12
Headings8/8
Technical16/25
E-E-A-T0/7
Images1/7
Links5/5
URL5/5
Social1/5
Freshness0/4
Mobile1/4
Indexability3/3
2
21tb.com21tb.com

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Title Length48 chars

Recommended: 50-60 chars (~293px / 580px)

Description Length81 chars

Recommended: 120-160 chars

Issues (1)

  • • Most images missing alt text (73/76) — critical for accessibility and SEO

9 issues found

Upgrade to view details

Crawlability

Sitemap

Type: standard

769 URLs

robots.txt

Local SEO

Local Search Readiness

5/100
Poor
2 13 2

This site doesn't appear to be a local business. Local SEO signals are optional for non-local websites.

Sponsored

AI & LLM Readiness

F32/100
Bot Access
20/25
Machine Read.
4/25
Schema Data
0/25
Citation
8/25

AI Bot Access

14/14 accessible
AI Search
OAI-SearchBot
PerplexityBot
Claude-SearchBot
Gemini-Deep-Research
DuckAssistBot
Training
GPTBot
ClaudeBot
Google-Extended
Meta-ExternalAgent
Bytespiderinfo
Amazonbot
Applebot-Extended
CCBotinfo
Fetch
ChatGPT-User

Machine Readability

llms.txt
llms-full.txt
Semantic HTML
Heading Hierarchy
Text ratio:0%
Words:251
Token eff.:Too Short

Structured Data

No Schema

Citation Readiness

Opening Summary169w
Descriptive Headingsavg 1w
Canonical URL
Open Graph0/3
Twitter Card0/3
Language Tag
Publish Date
Author Info
Lists
Tables
TL;DR / Summary
About Page Link
Recommendations (12)
AI readiness recommendation preview...
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Accessibility

WCAG 2.1 Compliance

Evaluates how accessible your website is for users with disabilities, based on WCAG 2.1 guidelines. Checks images, forms, keyboard navigation, ARIA roles, and color contrast.
D
48/100
7
Passed
5
Critical
1
Warnings
Images & Alt Text
5/20
Checks if images have descriptive alt text for screen readers and visually impaired users.
Semantic Structure
11/20
Evaluates proper use of HTML5 semantic elements (header, nav, main, footer) and heading hierarchy.
Forms & Inputs
5/15
Verifies form fields have labels, error messages are clear, and inputs are properly associated.
Color & Contrast
15/15
Tests text-to-background color contrast ratios against WCAG AA/AAA minimum requirements.
Keyboard & Focus
11/15
Ensures all interactive elements are reachable and operable via keyboard (tab, enter, escape).
ARIA & Roles
1/15
Checks correct use of WAI-ARIA attributes (roles, states, properties) for assistive technologies.
3 recommendations
  • •Accessibility recommendation preview...
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Carbon Footprint

SWDM v4 · Eco-Score

Carbon emissions estimated using the Sustainable Web Design Model v4 (SWDM v4). Factors in data center, network, and device energy across new and returning visitors. Grade thresholds based on HTTP Archive percentiles.
64/100
A+
8 mg
CO₂e / view
65.4 KB
Page Weight
95%
Cleaner Than
New Visitor
9 mg
vs
Returning (cached)
5 mg
Annual (10K/mo)
972 g
Emission Segments
Data Center
2 mg
Network
2 mg
Device
4 mg
Resource Breakdown
HTML
60.2 KB
Other
5.3 KB
Green Hosting Not Verified
ChinaNetCenter Ltd.
4 recommendations
  • •Carbon footprint recommendation preview...
Upgrade to view recommendations
F

Security Score

31%Critical
Interactive

HTTPS

No WAF

22d

Certificate Details

Type

Organization Validated (OV)

Certificate Authority

DigiCert, Inc.

Key Algorithm

RSA (2048 bit)

Signature

SHA-256 with RSA

TLS Version

TLSv1.2

HTTP Protocol

HTTP/1.1

Valid From

06.06.2025

Valid Until

22.06.2026

OCSP Stapling

Enabled

Subject Alternative Names (2)

*.21tb.com21tb.com

SHA-256 Fingerprint

7F:AA:32:F0:56:D0:DF:BE:29:FA:C0:DF:85:DA:CE:8E:7F:C9:B3:C3...

Top Recommendations

Security recommendation preview

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HTTP Headers

Developer Console

cache-flow
9922414689
connection
keep-alive
content-encoding
📦 Gzip(gzip)
content-type
text/html; charset=UTF-8
date
Sat, 30 May 2026 12:46:51 GMT
fai-cache-status
SRC_NOT_UPDATE
Good Warning Issue

Email Infrastructure

Custom Mail Server

Score

75

SPF
DKIM
DMARC

MX Records (1)

mx-antispam.21tb.com

Domain Information

21tb.com

Domain Age
23y 9m

Created

16.08.2002

Expires

16.08.2028

Last Updated

18.09.2025

Registrar

Xin Net Technology Corporation

DNSSEC
Not Enabled

Mobile Compatibility

Viewport & Responsive Test

Tests how well your website works on mobile devices. Checks viewport configuration, responsive layout, touch targets, font readability, and simulates rendering across different screen sizes.
D
58/100
Mobile Friendly1 breakpoint
Viewport Meta
The viewport meta tag tells mobile browsers how to scale the page. Without it, mobile devices render at desktop width.
Responsive Design
Uses CSS media queries or flexible layouts to adapt content to different screen sizes automatically.
Touch Icons
Apple touch icons and favicons displayed when users add the site to their home screen on mobile devices.
Readable Font Size
Base font size should be at least 16px on mobile to ensure text is readable without zooming.
Relative Units
Using em, rem, %, or vw instead of fixed px values allows content to scale properly across screen sizes.
No H-Scroll Risk
No elements wider than the viewport that would cause horizontal scrolling on mobile devices.
Tap Targets OK
Interactive elements (buttons, links) are at least 48x48px with enough spacing to prevent accidental taps.
No Fixed Widths
No elements with fixed pixel widths that could overflow on smaller screens and break the layout.
Viewport
width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0
2 recommendations
  • •Mobile compatibility recommendation preview...
Upgrade to view recommendations

Typography & Readability

微软雅黑

WCAG Partial
64/100
Readability
/30
21/30

18px · LH 1.50

Hierarchy
/20
8/20
WCAG
/25
17/25

1:1 min contrast

Performance
/25
18/25

2 fonts · 5 req

Heading Font

微软雅黑

Sans0

Body Font

微软雅黑

Sans18px

Contrast Ratio

1:1

6 issues

Reading Comfort

Single Font Family

left aligned
16px
h1
20px
h2
14px
h3
16px
h4
18px
p

✅ Excellent readability: 18px body text is ideal for all devices.

✅ Optimal line spacing: 1.50 ratio (ideal range 1.4–1.6).

⚠️ Partial contrast: 6 elements below WCAG AA threshold (min 1.0:1).

❌ Missing H1: Every page should have exactly one H1 element for SEO and accessibility.

✅ Lean font stack: 2 font families keeps load times fast.

✅ Smart font loading: font-display: swap prevents invisible text during load (FOIT).

Buy on MyFonts

Color Palette

4 unique colors
Light
#ffffff
Background· 36.10000000000001%
#e9f3fe
Primary· 43.800000000000004%
#c4e4fd
Accent· 15.7%
#7f90bc
Secondary· 4.5%

Business & Marketing Stack

1 Tools Detected

Growing

Behavior Analytics

1
Google AnalyticsFree

User behavior and product analytics

1

Categories

1

Total Tools

0

Enterprise

0

Mid-Market

Assessment: Growing marketing technology adoption

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Scripts & Styles

15 Resources

11
Scripts
4
Styles
1
Async
1
Defer

Top Script Sources

jzfe.faisys.com(4)webchat.7moor.com(3)0.ss.508sys.com(3)hm.baidu.com(1)

Website Identity

21tb.com

[email protected]
23 years old
Location detected: 🇨🇳 Chinavia ip
Xin Net Technology Corporationzh

Social Profiles

X (Twitter)

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Last analyzed: 31 May 2026 at 12:44

Historical Analysis & Change Tracking