StackOptic
Back to Search
serlo.org favicon

serlo.org

https://serlo.org· First analyzed 09 May 2026· Updated 09 May 2026
Export
serlo.org
Desktop screenshot of serlo.org
Mobile screenshot of serlo.org
Mobile

Sponsored

Hosting Provider

Cloudflare
cloudflare.com

IP Address

104.26.15.243

Site Location

🇩🇪 München, Germanyvia schema_nap

Server Location

🇨🇦 Toronto, Canada

ASN

AS13335

Organization

Cloudflare, Inc.

Server

Cloudflare

CDN

Cloudflare

WAF

Cloudflare

Nameservers

norm.ns.cloudflare.com.kara.ns.cloudflare.com.

Performance

100

Core Web Vitals

Weight

First Contentful Paint
638 ms10%
Speed Index
829 ms10%
Largest Contentful Paint
—25%
Total Blocking Time
0.0 ms30%
Cumulative Layout Shift
0.00025%
433 KB
53 requests

Image Optimization

Lazy LoadResponsiveVercel Image Optimization
0–49
50–89
90–100

Architecture Stack

Hybrid
⚡ SSG
Frontend
Framework
Next.js
Styling
Tailwind CSS
Infrastructure
Platform
Vercel
CDN
Cloudflare

Progressive Web App

Web ManifestApple Touch IconTheme Color

Technology Stack

7 Technologies Detected

Meta Frameworks

1
Next.js

Other

1
D3.js

CSS Frameworks

1
Tailwind CSS

Icon Libraries

1
Font Awesome

Email Marketing

1
Mailchimp

CDN

1
Cloudflare

Analytics

1
Sentry

SEO Analysis

C67/100
20
8
0
Meta Tags8/15
Content8/12
Headings8/8
Technical19/25
E-E-A-T0/7
Images4/7
Links5/5
URL5/5
Social3/5
Freshness0/4
Mobile4/4
Indexability3/3
S
serlo.orgserlo.org

Serlo – Die freie Lernplattform

Die freie Lernplattform

Title Length31 chars

Recommended: 50-60 chars (~186px / 580px)

Description Length23 chars

Recommended: 120-160 chars

Issues (0)

    8 issues found

    Upgrade to view details

    Crawlability

    Sitemap

    Type: standard

    13,531 URLs

    robots.txt

    18 rules

    Sitemap reference found

    Local SEO

    Local Search Readiness

    17/100
    Poor
    5 14 1

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

    Sponsored

    AI & LLM Readiness

    D41/100
    Bot Access
    20/25
    Machine Read.
    7/25
    Schema Data
    0/25
    Citation
    14/25

    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
    nav
    Text ratio:1%
    Words:208
    Token eff.:Too Short
    Sections/1K:33.7
    Depth:1/5

    Structured Data

    1 JSON-LD

    Citation Readiness

    Opening Summary14w
    Descriptive Headingsavg 3.8w
    Canonical URL
    Open Graph3/3
    Twitter Card0/3
    Language Tag
    Publish Date
    Author Info
    Lists
    Tables
    TL;DR / Summary
    About Page Link
    Recommendations (9)
    AI readiness recommendation preview...
    Upgrade to view recommendations

    Sponsored

    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.
    A
    80/100
    13
    Passed
    2
    Critical
    1
    Warnings
    Images & Alt Text
    13/20
    Checks if images have descriptive alt text for screen readers and visually impaired users.
    Semantic Structure
    20/20
    Evaluates proper use of HTML5 semantic elements (header, nav, main, footer) and heading hierarchy.
    Forms & Inputs
    10/15
    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
    13/15
    Ensures all interactive elements are reachable and operable via keyboard (tab, enter, escape).
    ARIA & Roles
    9/15
    Checks correct use of WAI-ARIA attributes (roles, states, properties) for assistive technologies.
    2 recommendations
    • •Accessibility recommendation preview...
    Upgrade to view recommendations

    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.
    80/100
    A
    44 mg
    CO₂e / view
    433.4 KB
    Page Weight
    90%
    Cleaner Than
    New Visitor
    50 mg
    vs
    Returning (cached)
    25 mg
    Annual (10K/mo)
    5.3 kg
    Emission Segments
    Data Center
    2 mg
    Network
    13 mg
    Device
    29 mg
    Resource Breakdown
    JavaScript
    245.8 KB
    Images
    31.6 KB
    CSS
    47.8 KB
    Fonts
    64.2 KB
    HTML
    44.2 KB
    Green Hosting Verified
    Cloudflare
    GWF Verified
    1 recommendation
    • •Carbon footprint recommendation preview...
    Upgrade to view recommendations
    D

    Security Score

    51%Poor
    Interactive

    HTTPS

    WAF

    34d

    Certificate Details

    Type

    Domain Validated (DV)

    Certificate Authority

    Google Trust Services

    Key Algorithm

    ECDSA (secp256r1) (256 bit)

    Signature

    ECDSA with SHA-256

    TLS Version

    TLSv1.3

    HTTP Protocol

    HTTP/2

    Valid From

    15.03.2026

    Valid Until

    13.06.2026

    OCSP Stapling

    Enabled

    Subject Alternative Names (2)

    serlo.org*.serlo.org

    SHA-256 Fingerprint

    C8:D5:EA:BE:AC:6B:3B:80:87:E2:A2:3F:68:2A:6E:73:FC:9F:1A:5B...

    Top Recommendations

    Security recommendation preview

    Upgrade to view recommendations
    Upgrade to view header details

    HTTP Headers

    Developer Console

    access-control-allow-origin
    *
    age
    3195976
    cache-control
    🟡 0s(public, max-age=0, must-revalidate)
    cf-cache-status
    DYNAMIC
    cf-ray
    9f91a9264d06783a-BOS
    content-disposition
    inline
    Good Warning Issue

    Email Infrastructure

    Google Workspace

    Score

    20

    SPF
    DKIM
    DMARC

    MX Records (5)

    alt1.aspmx.l.google.com
    alt2.aspmx.l.google.com
    alt4.aspmx.l.google.com
    alt3.aspmx.l.google.com

    +1 more

    Domain Information

    serlo.org

    Domain Age
    23y 10m

    Created

    17.07.2002

    Expires

    17.07.2026

    Last Updated

    19.01.2024

    Registrar

    OVH sas

    DNSSEC
    Not Enabled

    Privacy & Compliance

    Cookie Consent Banner
    Privacy Policy
    Terms of Service

    GDPR Indicators

    Privacy policy page linked

    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.
    A
    80/100
    Mobile Friendly4 breakpoints
    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
    1 recommendation
    • •Mobile compatibility recommendation preview...
    Upgrade to view recommendations

    Typography & Readability

    Karla

    WCAG Partial
    61/100
    Readability
    /30
    15/30

    36px · LH 1.11

    Hierarchy
    /20
    14/20

    1.33x ratio · ✓ H1→H6

    WCAG
    /25
    14/25

    1.64:1 min contrast

    Performance
    /25
    18/25

    1 font · 2 req

    Heading Font

    Karla

    Sans48px

    Body Font

    Karla

    Sans36px

    Contrast Ratio

    1.64:1

    8 issues

    Reading Comfort

    Single Font Family

    center aligned
    48px
    h1
    21px
    h2
    36px
    h3
    36px
    p
    Minor Second
    Scale

    ✅ Excellent readability: 36px body text is ideal for all devices.

    ⚠️ Tight line spacing (1.11). Increase to 1.4–1.6 for better readability.

    ❌ Very complex text: Flesch score 24/100. Consider shorter sentences and simpler words.

    ⚠️ Partial contrast: 8 elements below WCAG AA threshold (min 1.6:1).

    ✅ Perfect heading hierarchy: Sequential h1→h2→h3 with single H1 — ideal for SEO & accessibility.

    ⚠️ Weak hierarchy: Headlines should be ≥2x body size for clear visual structure.

    Buy on MyFontsFlesch 25

    Color Palette

    6 unique colors
    7.2:1 AAA Light
    #ffffff
    Background· 84.50000000000001%
    #545859
    Other· 2.2%
    #007ec1
    Primary· 0%
    #d5f6ef
    Primary· 7.300000000000001%
    #89a3aa
    Secondary· 2.4%
    #bedbe0
    Secondary· 1.9%

    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

    Sponsored

    Scripts & Styles

    21 Resources

    20
    Scripts
    1
    Styles
    1
    Async
    14
    Defer

    Top Script Sources

    local(19)sa.serlo.org(1)

    Website Identity

    Serlo Education e.V.

    Serlo Education e.V.

    Serlo.org bietet einfache Erklärungen, Kurse, Lernvideos, Übungen und Musterlösungen mit denen Schüler*innen und Studierende nach ihrem eigenen Bedarf und in ihrem eigenen Tempo lernen können. Die Lernplattform ist komplett kostenlos und werbefrei.

    serlo@chancenwerk.org
    de.serlo.org/
    23 years old

    Daiserstraße 15 (RGB), München

    81371, München, Bayern

    Germany

    Location detected: 🇩🇪 Germany, Münchenvia schema_nap
    OVH sas📧 Google Workspacede

    Social Profiles

    GitHub

    Sponsored

    Last analyzed: 09 May 2026 at 15:16

    Historical Analysis & Change Tracking