— tools
whatsmydns.netdns
Global DNS propagation checker — see if your changes have hit worldwide
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DNS Checkerdns
Check A, CNAME, MX, NS, TXT records across global DNS servers
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MX Toolboxdns
MX, SPF, DKIM, DMARC lookup — email DNS health and blacklist check
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What Is My IPdns
Your public IP address, ISP, and geolocation info
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Down For Everyone?dns
Instantly check if a site is down globally or just for you
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SSL Labs Testdns
Deep SSL/TLS certificate analysis and security grade
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ICANN WHOIS Lookupdns
Domain registrar, expiry date, nameservers, registration info
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Redirect Pizzadns
Trace redirect chains — check 301/302 hops and final destination
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— tools
PageSpeed Insightsspeed
Google's CWV scorer — LCP, TBT, CLS, mobile vs desktop breakdown
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GTmetrixspeed
Speed grade, waterfall chart, render timeline — the full picture
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WebPageTestspeed
Advanced perf testing — filmstrip, TTFB, repeat view, multi-location
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Squooshspeed
Browser-based image compression — WebP, AVIF, side-by-side preview
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TinyPNGspeed
Fast PNG/JPG compression — drag drop, instant download
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Pingdomspeed
Speed test + uptime monitoring from multiple global locations
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Bundlephobiaspeed
Check the real cost of any npm package before you install it
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CF Browser Insightsspeed
Real user monitoring — actual visitor performance data via Cloudflare
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— tools
W3C HTML Validatorhtml
Official W3C markup validator — catch HTML errors and warnings
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W3C CSS Validatorcss
Validate CSS stylesheets for errors and spec compliance
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CodePenhtml
HTML/CSS/JS sandbox — build, test, and share front-end snippets live
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CSS-Trickscss
The CSS reference — guides, almanac, flexbox/grid deep dives
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Flexbox Froggycss
Learn flexbox by playing — fastest way to get it to stick
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CSS Gradientcss
Visual CSS gradient generator — linear, radial, copy-ready code
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Autoprefixercss
Add vendor prefixes to CSS automatically — browser compatibility fix
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Can I Usehtml
Browser support tables for HTML, CSS, JS — before you ship anything
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HTML Formatterhtml
Beautify or minify HTML — clean up messy markup instantly
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Meta Tags Previewhtml
Preview how your meta/OG tags look on Google, Twitter, Facebook
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— tools
JSFiddlejs
Quick JS/HTML/CSS sandbox — test snippets without a project setup
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JSON Lintjs
Validate and format JSON — catch syntax errors instantly
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Regex101js
Build, test, and debug regex with real-time match highlighting and explanation
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Prettier Playgroundjs
Format JS, HTML, CSS, JSON, Markdown — Prettier in the browser
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Babel REPLjs
Transpile modern JS to browser-compatible code — see output live
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JS Binjs
Live JS editor with shareable URLs — great for quick collabs
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Code Beautifyjs
Format JSON, XML, HTML, CSS, SQL — plus converters and diff tools
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DevDocsjs
Fast offline-capable API docs — JS, HTML, CSS, PHP, Python, all in one
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— tools
Security Headerssecurity
Grade your HTTP security headers — CSP, HSTS, X-Frame, referrer policy
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SSL Labssecurity
Deep SSL/TLS analysis — cipher suites, cert chain, protocol support
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SPF Record Checksecurity
Validate SPF records — prevent email spoofing and deliverability issues
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DMARC Checkersecurity
Check DMARC policy — protect your domain from email fraud
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VirusTotalsecurity
Scan URLs or files for malware across 70+ antivirus engines
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Mozilla Observatorysecurity
Full security scan — headers, TLS, cookies, redirects, graded report
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— tools
WAVE Checkera11y
Visual accessibility audit — errors, alerts, structure, contrast in one view
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Contrast Checkera11y
Check foreground/background color contrast ratios for WCAG compliance
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A11Y Checklista11y
Practical WCAG checklist — manual audit reference for every build
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Accessibility Insightsa11y
Microsoft's accessibility tool — automated + guided manual testing
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Color Blind Simulatora11y
Preview your site through different types of color blindness
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tota11ya11y
Khan Academy's a11y viz toolkit — overlay headings, labels, and contrast on any page
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