developer.mozilla.org website health report
Website health report
developer.mozilla.org scores 96/100
Outstanding — this site is in excellent health. We found 7 issues; the weakest area is Performance (91/100).
- 1 Medium
- 6 Low
- 34 Passed
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Matched SuperSiteBros services
Site crawl
- Pages crawled
- 25
- Broken links
- 0
- Redirect chains
- 0
- Missing titles
- 0
- Duplicate titles
- 0
- Missing descriptions
- 0
- Missing H1
- 0
- Thin pages
- 0
- Noindex pages
- 0
- Mixed content pages
- 0
Pages checked
| Page | Status | Title | Words | Issues |
|---|---|---|---|---|
| /en-US/ | 200 | MDN Web Docs | 813 | — |
| /en-US/docs/Web/HTML | 200 | HTML: HyperText Markup Language | MDN | 1491 | — |
| /en-US/docs/Web/HTML/Reference/Elements | 200 | HTML elements reference - HTML | MDN | 4916 | — |
| /en-US/docs/Web/HTML/Reference/Global_attributes | 200 | Global attributes - HTML | MDN | 2495 | — |
| /en-US/docs/Web/HTML/Reference/Attributes | 200 | HTML attribute reference - HTML | MDN | 3399 | — |
| /en-US/docs/Web/HTML/Reference | 200 | HTML reference - HTML | MDN | 607 | — |
| /en-US/docs/Web/HTML/Guides/Responsive_images | 200 | Using responsive images in HTML - HTML | MDN | 3389 | — |
| /en-US/docs/Web/HTML/Guides/Cheatsheet | 200 | HTML cheatsheet for syntax and common tasks - HTML | MDN | 1040 | — |
| /en-US/docs/Web/HTML/Guides/Date_and_time_formats | 200 | Using date and time formats in HTML - HTML | MDN | 3085 | — |
| /en-US/docs/Web/HTML/Guides | 200 | HTML guides - HTML | MDN | 1049 | — |
| /en-US/docs/Web/SVG | 200 | SVG: Scalable Vector Graphics | MDN | 993 | — |
| /en-US/docs/Web/MathML | 200 | MathML | MDN | 1041 | — |
| /en-US/docs/Web/XML | 200 | XML: Extensible Markup Language | MDN | 529 | — |
| /en-US/docs/Web/CSS | 200 | CSS: Cascading Style Sheets | MDN | 1392 | — |
| /en-US/docs/Web/CSS/Reference/Properties | 200 | CSS properties - CSS | MDN | 1592 | — |
| /en-US/docs/Web/CSS/Reference/Selectors | 200 | CSS selectors - CSS | MDN | 893 | — |
| /en-US/docs/Web/CSS/Reference/At-rules | 200 | CSS at-rules - CSS | MDN | 928 | — |
| /en-US/docs/Web/CSS/Reference/Values | 200 | CSS values - CSS | MDN | 832 | — |
| /en-US/docs/Web/CSS/Reference | 200 | CSS reference - CSS | MDN | 3422 | — |
| /en-US/docs/Web/CSS/Guides/Box_model/Introduction | 200 | Introduction to the CSS box model - CSS | MDN | 1208 | — |
| /en-US/docs/Web/CSS/Guides/Animations/Using | 200 | Using CSS animations - CSS | MDN | 3575 | — |
| /en-US/docs/Web/CSS/Guides/Flexible_box_layout/Basic_concepts | 200 | Basic concepts of flexbox - CSS | MDN | 4107 | — |
| /en-US/docs/Web/CSS/Guides/Colors/Applying_color | 200 | Applying color to HTML elements using CSS - CSS | MDN | 2561 | — |
| /en-US/docs/Web/CSS/Guides | 200 | CSS guides - CSS | MDN | 3600 | — |
| /en-US/docs/Web/CSS/How_to/Layout_cookbook/Column_layouts | 200 | Column layouts - CSS | MDN | 1895 | — |
Issues to fix on developer.mozilla.org
MediumRender-blocking scripts and stylesheetsPerformance
0 blocking script(s) and 20 stylesheet(s) in the page head.
Why it matters
Scripts in the <head> without async/defer, and stylesheets, must download before the browser paints anything.
How to fix it
Add `defer` to scripts that don’t need to run early, inline small critical CSS, and load the rest asynchronously.
LowFirst large image is lazy-loadedPerformance
The first image in the page is marked loading="lazy".
Why it matters
The first image is often the Largest Contentful Paint element. Lazy-loading it delays the most important paint.
How to fix it
Remove loading="lazy" from the first visible image and consider `fetchpriority="high"`.
Details
- https://developer.mozilla.org/static/ssr/mdn_contributor.9e2a105f50828d5a.png
LowNo security.txt fileBest practices
/.well-known/security.txt was not found (or has no Contact: line).
Why it matters
security.txt (RFC 9116) tells researchers how to report a vulnerability to you instead of disclosing it publicly or not at all.
How to fix it
Publish /.well-known/security.txt with at least a `Contact:` and an `Expires:` line.
LowNo Permissions-PolicySecurity
No Permissions-Policy header.
Why it matters
Permissions-Policy switches off powerful browser features (camera, microphone, geolocation, payment…) that your site doesn’t use, so injected or third-party code can’t use them either.
How to fix it
Send e.g. `Permissions-Policy: camera=(), microphone=(), geolocation=(), payment=(), usb=()`, allowing only what you need.
LowTitle is very shortSEO
“MDN Web Docs” is 12 characters.
Why it matters
A very short title wastes space in search results that could explain what the page offers.
How to fix it
Expand it to roughly 30–60 characters: main topic first, brand last.
LowMissing Open Graph tagsSEO
Missing: og:title, og:description, og:image.
Why it matters
Open Graph tags control the title, description and image when your page is shared on Facebook, LinkedIn, Slack, iMessage and others. Without them, shares look bare or pick a random image.
How to fix it
Add og:title, og:description, og:image (1200×630) and og:url.
LowNo structured dataSEO
No JSON-LD or microdata found.
Why it matters
Structured data (schema.org JSON-LD) helps search engines understand your organisation, articles, products or FAQs and can unlock rich results.
How to fix it
Add JSON-LD for your organisation/website, plus the type that fits each page (Article, Product, LocalBusiness…). Check it with Google’s Rich Results Test.
InfoNot ready for the HSTS preload listSecurity
For preload the header still needs: includeSubDomains, preload.
Why it matters
Preloading bakes your domain into browsers as HTTPS-only, protecting even the very first visit. It’s optional and hard to undo, so only do it once every subdomain supports HTTPS.
How to fix it
Serve `max-age=31536000; includeSubDomains; preload` on the root domain, redirect http→https on the same host first, then submit at hstspreload.org.
No issues match these filters.
Passed checks (34)
- Valid SSL certificate — Trusted certificate for developer.mozilla.org, valid until 2026-12-22 (55 days left), issued by Let's Encrypt.
- HTTP redirects to HTTPS — http://developer.mozilla.org/ → https://developer.mozilla.org/ (301).
- HSTS enabled — Strict-Transport-Security: max-age=63072000
- Content-Security-Policy restricts scripts — default-src 'self'; script-src 'report-sample' 'self' 'wasm-unsafe-eval' assets.codepen.io production-assets.codepen.io https://js.stripe.com transcend-cdn.com 'sha256-XNBp89FG76amD8BqrJzyflxOF9PaWPqP
- Clickjacking protection — X-Frame-Options: DENY
- MIME sniffing disabled — X-Content-Type-Options: nosniff
- Referrer-Policy set — strict-origin-when-cross-origin
- No mixed content — Every resource referenced in the HTML uses https://.
- Fast server response — Time to first byte 0.03s.
- Brotli compression — Content-Encoding: br
- HTTP/2 supported — Served over HTTP/2.
- Lean HTML — The HTML document is 114.4 KB.
- Static files are cacheable — 4 sampled CSS/JS files have long cache lifetimes.
- Page loads successfully — HTTP 200 after 1 redirect(s).
- Page is indexable — No noindex directive in meta robots or X-Robots-Tag.
- Good meta description — 145 characters.
- One clear H1 — “Resources for Developers, by Developers”
- Canonical URL set — https://developer.mozilla.org/en-US/
- Mobile viewport set — width=device-width, initial-scale=1.0
- robots.txt allows crawling — 1 rule group(s).
- XML sitemap found — https://developer.mozilla.org/sitemap.xml (index with 10 entries).
- Missing pages return 404 — A made-up URL returned 404.
- Page language declared — lang="en-US"
- All images have alt attributes — 1 images checked.
- Form fields are labelled — 1 fields checked.
- Links and buttons have names
- Logical heading structure — 13 headings in order.
- Standards-mode HTML5 document — Doctype and charset are declared.
- SPF record present — v=spf1 include:%{i}._ip.%{h}._ehlo.%{d}._spf.vali.email include:_spf.mozilla.com include:_spf.google.com include:spf.fundraiseup.com ~all
- DMARC policy enforced — v=DMARC1; p=reject; pct=100; adkim=r; aspf=r; rua=mailto:dmarc_agg@vali.email,mailto:dmarc@mozilla.com
- CAA records restrict certificate issuance — issue letsencrypt.org; issue amazon.com; iodef mailto:foxsec+caaiodef@mozilla.com; issue amazontrust.com
- Reachable over IPv6 — developer.mozilla.org has an AAAA record.
- No broken links found — Checked 25 page(s) and 60 linked URL(s).
- Page titles are unique — Across 25 crawled page(s).
Site facts
- Final URL
- https://developer.mozilla.org/en-US/
- HTTP status
- 200
- Server response (TTFB)
- 29 ms
- Protocol
- HTTP/2
- Compression
- br
- HTML size
- 114.4 KB
- DOM elements
- 820
- Words on page
- 813
- Certificate
- Valid, 55 days left (Let's Encrypt)
- Email DNS
- SPF ✓ · DMARC ✓ · CAA ✓ · IPv6 ✓
- Server
- Google Frontend
Technology detected
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