UD5 Toolkit
HTTP Security Header Checker - Online HSTS, CSP, X-Frame Analysis
Paste response headers string and get a security audit. Check presence and configuration of key security headers. Local analysis.
Tag: Checker - Validator & Tester
43+ toolsAustralia Public Holiday Checker - Online by State & Year
Select a state and year to see all public holidays. Works offline with built-in data. Plan your long weekends. Simple reference tool.
UK Tax Code Checker - Online Understand Your Code
Enter your UK tax code and see an explanation of what the numbers and letters mean. Simple educational reference. No data stored.
Blood Donation Eligibility Checker - Online Quick Questionnaire
Answer a short questionnaire based on common deferral criteria (travel, medication, tattoos) to see if you may be eligible to donate blood. Educational only.
Basic Grammar Checker - Online Free Writing Assistant
Identify common grammar mistakes (subject-verb agreement, tense, articles) with simple rule-based analysis. Explanations provided. Not AI, purely rule-based and local.
Email Spam Trigger Checker - Online Avoid Spam Filters
Paste your email subject and body. The tool highlights common spam trigger words and gives a risk score. Improve inbox placement.
SSL Certificate Checker - Online Verify Expiry & Chain
Enter a domain and see its SSL certificate details: issuer, validity dates, and chain. Client‑side fetch.
Real‑Sample Contrast Checker - Online See Paragraph
See how a full paragraph looks with your chosen text and background colors. Not just a ratio; the real appearance.
Broken Image Finder - Online Check Page for Missing Pictures
Enter a URL and get a list of all images that fail to load (404, CORS). A simple asset audit tool. Runs in your browser.
Color Contrast Ratio Tester - Online WCAG AA/AAA Check
Enter foreground and background colors to instantly see the contrast ratio and pass/fail for AA and AAA. Simple and fast.
SSL Cipher Suite Checker - Online Test TLS Security
Check which cipher suites a website supports and identify weak or outdated ones. Quick security audit from your browser.
Notification Permission Checker - Online Manage & Test
See your current notification permission status. Request or reset it. Test browser notification behavior.
DNS Propagation Checker - Online Verify Record Status
Query a domain's DNS record against multiple public resolvers (Google, Cloudflare) and see how it propagates. Client‑side fetch.
Bulk Color Contrast Checker - Online WCAG Validation
Paste a list of foreground/background color pairs and instantly see which pass AA/AAA. Perfect for checking entire style guides.
Blood Pressure Category Checker - Online AHA & ESC Guideline Tool
Interpret your blood pressure reading based on American Heart Association and European Society of Cardiology categories. Visual gauge with actionable health insights.
Password Pwned? Checker - Online k‑Anonymity
Check if a password appears in the Have I Been Pwned database using k‑Anonymity. Only the first 5 characters of the hash are sent.
HSTS Header Checker - Online Strict‑Transport‑Security
Fetch a site’s HSTS header and validate its syntax, max‑age, and subdomain flags. Ensure your site enforce HTTPS.
Mersenne Prime Checker - Online 2^p‑1 Validation
Check if a number of the form 2^p‑1 is a Mersenne prime. Quick Lucas‑Lehmer test simulation for small p.
PWA Install Prompt Checker - Online See beforeinstallprompt Status
Check if the browser has captured the beforeinstallprompt event. Understand why your PWA is (or isn't) installable.
API Status Checker - Online Test Endpoint & Response
Enter an API URL and quickly check its HTTP status code and response time. See response headers and body. Browser fetch.
Accessible Color Contrast Grid - Online Test Combinations
Enter a palette of colors and see a grid showing whether each foreground/background pair passes AA or AAA contrast. Must for designers.
Live Website Audit Checker - Online Quick SEO & Performance
Enter a URL and get a one‑page report of titles, description, headings, image alts, and broken links. All from browser.
Password Policy Checker - Online Test Against Rules
Define minimum length, uppercase, digits, special chars, and check if a password meets your custom policy. Instant feedback.
Favicon Checker - Online Test Any Site's Icon
Enter a URL and see its favicon at all standard sizes. Check if it's properly defined. SEO basic check.
Local Password Breach Checker - Online k‑Anonymity
Tell if your password has appeared in data breaches without sending the full password. Uses hash prefix locally.
HTTP Redirect Path Tracer - Online SEO Chain Analyzer
Trace the full redirect path of a URL. See every hop, status code, and final destination. Detect broken chains.
Font Fallback Checker - Online See Missing Glyphs
Type any character and see how it renders in different font stacks. Detect missing glyphs and fallback behavior.
IBAN Structure Checker - Online Validate Format & Country
Check if an IBAN has the correct length and structure for its country. Early validation, no bank connection.
Email Spam Score Checker - Online Newsletter Tester
Paste your email body and subject, and get a spam score based on common trigger words and patterns. Improve your cold outreach.
URL Status Code Checker - Online Bulk HTTP Response Tool
Check HTTP status codes for multiple URLs at once. Identify broken links and redirects. All requests made via browser fetch.
Canonical Tag Checker - Online Rel=Canonical Inspector
Check a live URL to extract and validate its canonical link element. Ensure correct SEO configuration. Runs from your browser.
Browser Extension Headers Check - Online Detect Injected Scripts
Look at HTTP headers and JavaScript objects to guess which browser extensions might be installed. For awareness.
Homophone Checker - Online Sound‑Alike Words Tool
Type a word to see all its homophones with definitions. Avoid embarrassing mistakes (their/there/they’re). Static dictionary.
Palindrome Checker - Online Test Words & Sentences
Check if a word or phrase is a palindrome (reads same forward and backward). Live validation and fun facts.
Gravatar Generator & Checker - Online Email to Avatar
Preview the Gravatar image associated with any email address. Generate the correct Gravatar URL. Handy for avatar debugging.
Leap Year Checker - Online Verify February 29
Enter a year to check if it is a leap year. Shows the rule explanation and next/previous leap years. Simple reference.
Password Strength Checker - Online Meter & Analyzer Tool
Evaluate the strength of your passwords with a visual meter and detailed feedback. Check for length, complexity, and breached passwords. All analysis is client-side.
Color Contrast Checker - Online WCAG Accessibility Validator
Check the contrast ratio between foreground and background colors to ensure web accessibility compliance. Get WCAG 2.1 AA/AAA pass/fail results instantly.
Image Format MIME Checker - Online Identify True Type
Drop an image that might have wrong extension and see its real format (JPEG, PNG, WebP) based on header bytes.
HTTP Headers Checker - Online Inspect URL Response Headers
Enter a URL and see the full HTTP response headers returned by the server. Detect redirects and server type. Useful for SEO and web debugging.
Is It Down or Just Me - Online Website Uptime Checker
Check if a website is globally reachable or experiencing issues. Status code and latency displayed. Quick browser-side test.
Isogram Checker - Online Words Without Repeating Letters
Find out if a word is an isogram (no repeating letters). Different types: first-order, second-order. Word nerd fun.
npm Version Range Checker - Online SemVer & Tilde Caret
Enter a package name and version range to see all satisfying versions from the registry. Understand ^ and ~.