htdp.org

https://htdp.org· First analyzed 12 May 2026· Updated 12 May 2026

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htdp.org

Mobile

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Hosting Provider

GitHub Pages

pages.github.com

IP Address

185.199.110.153

Site Location

🇺🇸 United Statesvia ip

Server Location

🇺🇸 San Francisco, United States

ASN

AS54113

Organization

GitHub, Inc

Server

GitHub.com

CDN

Fastly

Nameservers

ns-cloud-b4.googledomains.com.ns-cloud-b1.googledomains.com.ns-cloud-b3.googledomains.com.ns-cloud-b2.googledomains.com.

Performance

100

Core Web Vitals

Weight

First Contentful Paint

241 ms10%

Speed Index

313 ms10%

Largest Contentful Paint

—25%

Total Blocking Time

0.0 ms30%

Cumulative Layout Shift

0.00025%

99 KB

4 requests

0–49

50–89

90–100

Architecture Stack

Monolithic

⚙️ SSR

Infrastructure

Platform

GitHub Pages

CDN

Fastly

SEO Analysis

F32/100

Meta Tags4/15

Content3/12

Headings0/8

Technical6/25

E-E-A-T0/7

Images4/7

Links3/5

URL5/5

Social0/5

Freshness0/4

Mobile4/4

Indexability3/3

htdp.orghtdp.org

How to Design Programs

No description available for this page.

Title Length22 chars

Recommended: 50-60 chars (~139px / 580px)

Description Length0 chars

Recommended: 120-160 chars

Issues (4)

• Missing meta description — important for click-through rates in SERPs
• Very thin content (14 words). Search engines need substantial content for ranking.
• Missing H1 tag — every page should have exactly one H1

13 issues found

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Crawlability

Sitemap

robots.txt

4 rules

Local SEO

Local Search Readiness

0/100

Poor

15 2

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

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AI & LLM Readiness

F22/100

Bot Access

20/25

Machine Read.

1/25

Schema Data

0/25

Citation

1/25

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:3%

Words:10

Token eff.:Too Short

Structured Data

No Schema

Citation Readiness

Opening Summary

Descriptive Headings

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.

63/100

Passed

Critical

Warnings

Images & Alt Text

20/20

Checks if images have descriptive alt text for screen readers and visually impaired users.

Semantic Structure

3/20

Evaluates proper use of HTML5 semantic elements (header, nav, main, footer) and heading hierarchy.

Forms & Inputs

15/15

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

9/15

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.

61/100

A+

12 mg

CO₂e / view

99.2 KB

Page Weight

95%

Cleaner Than

New Visitor

14 mg

Returning (cached)

7 mg

Annual (10K/mo)

1.5 kg

Emission Segments

Data Center

3 mg

Network

3 mg

Device

7 mg

Resource Breakdown

Images

98.2 KB

HTML

1.0 KB

Green Hosting Not Verified

GitHub Pages

3 recommendations

•Carbon footprint recommendation preview...

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Security Score

71%Good

Static / Informational

HTTPS

No WAF

73d

Certificate Details

Type

Domain Validated (DV)

Certificate Authority

Let's Encrypt

Key Algorithm

RSA (2048 bit)

Signature

SHA-256 with RSA

TLS Version

TLSv1.3

HTTP Protocol

HTTP/2

Valid From

25.04.2026

Valid Until

24.07.2026

Subject Alternative Names (2)

htdp.orgwww.htdp.org

SHA-256 Fingerprint

29:24:36:9B:72:4D:58:5D:59:3C:50:AB:FA:D8:B1:6F:B5:20:27:3A...

Recommendations

Security recommendation preview

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HTTP Headers

Developer Console

accept-ranges

bytes

access-control-allow-origin

age

cache-control

🟡 600s(max-age=600)

content-encoding

📦 Gzip(gzip)

content-length

756

Good Warning Issue

Email Infrastructure

Google Workspace

Score

SPF

DKIM

DMARC

MX Records (5)

alt2.aspmx.l.google.com

aspmx.l.google.com

alt4.aspmx.l.google.com

alt3.aspmx.l.google.com

+1 more

Domain Information

htdp.org

Domain Age

24y 10m

Created

29.06.2001

Expires

29.06.2026

Last Updated

17.07.2025

Registrar

Squarespace Domains II LLC

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.

29/100

Not Mobile Friendly

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.

5 recommendations

•Mobile compatibility recommendation preview...

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Typography & Readability

Times New Roman

WCAG Partial

63/100

Readability

/30

22/30

16px · LH --

Hierarchy

/20

10/20

WCAG

/25

17/25

1.25:1 min contrast

Performance

/25

14/25

1 font

Heading Font

Times New Roman

Body Font

Times New Roman

Serif16px

Contrast Ratio

1.25:1

3 issues

Reading Comfort

Single Family

left aligned

16px

✅ Excellent readability: 16px body text is ideal for all devices.

⚠️ Partial contrast: 3 elements below WCAG AA threshold (min 1.2:1).

✅ Lean font stack: 1 font families keeps load times fast.

⚠️ Missing font-display: swap — users may see invisible text while fonts load (FOIT).

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Color Palette

9 unique colors

Light

#ffffff

Background· 66.5%

#734cbd

Primary· 14.7%

#231845

Secondary· 5%

#4c3a79

Secondary· 3.3%

#9b8dbe

Secondary· 2.7%

#160f32

Accent· 2.1%

#8167bd

Secondary· 1.8%

#d6cee2

Secondary· 0.8%

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Website Identity

htdp.org

24 years old

Location detected: 🇺🇸 United Statesvia ip

Squarespace Domains II LLC📧 Google Workspace

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Last analyzed: 12 May 2026 at 11:38

Historical Analysis & Change Tracking