atcoder.jp
AtCoder
Last scanned Jul 26, 2026, 5:17 AM · 1 view
Overall score
Fair
Summary
AtCoder is a programming contest site for anyone from beginners to experts. This website uses Nginx behind CloudFront CDN. SEO is fair (65/100) and accessibility is fair (50/100). Security scores excellent (90/100) and performance excellent (100/100). Top issue: Missing canonical link.
AtCoder is a programming contest site for anyone from beginners to experts. We hold weekly programming contests online.
Top issues to fix
9 issues found · 3 high priority
Missing Content-Security-Policy header
SecurityAdd a CSP to control which sources can run scripts — the strongest single defense against XSS.
No H1 heading found
SEOAdd exactly one H1 describing the page's main topic — it anchors the document outline for search engines and screen readers.
Over half of images are missing alt text
AccessibilityAdd alt attributes to images — screen readers depend on them, and they help image SEO.
Missing canonical link
SEOAdd <link rel="canonical"> so search engines know which URL variant to index.
No structured data (JSON-LD) found
SEOAdd JSON-LD (Organization, Article, Product…) to become eligible for rich results.
robots.txt not found
SEOPublish /robots.txt with a Sitemap: directive to guide crawlers.
+3 more issues — details in the sections below.
SEO
5 issue(s) found
Performance
289 ms
Security
HTTPS & header checks
Accessibility
3 issue(s) found
Organization
Company details published in this site's own structured data.
AtCoder is a programming contest site for anyone from beginners to experts. We hold weekly programming contests online.
Meta tags
- Title
- AtCoder
- Description
- AtCoder is a programming contest site for anyone from beginners to experts. We hold weekly programming contests online.
- Canonical
- Language
- Charset
- utf-8
- Viewport
- width=device-width,initial-scale=1.0
- Robots meta
- noai, noimageai
- Manifest
Technologies
Detected frameworks, languages, and tools.
Hosting & CDN
- Hosting provider
- —
- CDN provider
- CloudFront
- IP address
- —
- ASN
- —
DNS records
| Type | Value |
|---|---|
| A | — |
| AAAA | — |
| MX | — |
| TXT | — |
| NS | — |
| CAA | — |
| CNAME | — |
| IPv6 support | No |
TLS / SSL certificate
- Version
- TLS 1.3
- Issuer
- Amazon
- Subject
- atcoder.jp
- Valid from
- Apr 2, 2026
- Valid to
- Oct 16, 2026
- Days until expiry
- 82
- SAN domains
- atcoder.jp
Security headers
- Strict-Transport-SecurityEnabled
- Content-Security-PolicyMissing
- X-Frame-OptionsEnabled
- X-Content-Type-OptionsEnabled
- Referrer-PolicyEnabled
- Permissions-PolicyMissing
Compression: gzip · 2 cookie(s) observed
Content & assets
Headings
H1 0 · H2 0 · H3 10
Links
78 internal · 18 external · 11 broken
Images
43 total · 43 missing alt
Scripts / Styles
19 scripts · 4 stylesheets
JS / CSS size
497 KB · 153 KB
Page size
46.8 KB
Robots.txt & Sitemap
- robots.txt
- Not found
- Disallow rules
- 0
- sitemap.xml
- Not found
- URLs in sitemap
- 0
SEO issues
- Missing canonical link
- No H1 heading found
- No structured data (JSON-LD) found
- robots.txt not found
- sitemap.xml not found
Accessibility issues
- Over half of images are missing alt text
- No H1 heading found
- Missing <html lang> attribute
Scan details
- Requested URL
- https://atcoder.jp
- Final URL
- https://atcoder.jp
- HTTP status
- 200
- HTTP version
- HTTP/2
- Response time
- 289 ms
- HTML size
- 46.8 KB
- Redirect chain
- https://atcoder.jp
See something wrong on this report? Request a correction
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Frequently asked questions
- What technology does atcoder.jp use?
- atcoder.jp is built with Bootstrap, jQuery, Google Analytics, Nginx.
- Is atcoder.jp secure (HTTPS)?
- Yes. atcoder.jp uses TLS 1.3 with a certificate issued by Amazon, valid until Oct 16, 2026.
- Who hosts atcoder.jp?
- Hosting provider information for atcoder.jp is not available yet.
- What is atcoder.jp's SEO score?
- atcoder.jp scored 65/100 for SEO in the latest analysis (fair).
- What is atcoder.jp's overall website score?
- atcoder.jp has an overall SiteGraph score of 77/100, combining SEO, performance, security, and accessibility.
OpenGraph & Twitter Card
OpenGraph
Twitter Card