UD5 Toolkit
Text Contrast Validator - Online WCAG AAA Checker
Enter a text color and background color and instantly see if the combination passes WCAG AA and AAA ratio. Safe colors.
Tag: Validator - JSON/HTML/CSS Code Checker
35+ toolsRobots.txt Validator & Parser - Online Check Syntax
Paste robots.txt content and parse it to check validity, find disallowed paths. Educational SEO tool. Local processing.
XML Sitemap Validator - Online Check Structure & Errors
Paste your sitemap XML and check for missing namespaces, invalid URLs, or size limit violations. Keep your SEO healthy.
JSON-LD Validator - Online Structured Data Syntax Checker
Paste JSON-LD and validate basic syntax and required properties for Article, Product, etc. Local only. Instant feedback.
GeoJSON Validator - Online Check Geometry & Properties
Paste a GeoJSON object and validate its structure. Catch missing coordinates, wrong types, and feature errors. Local.
Web App Manifest Validator - Online Check PWA Manifest
Paste your manifest.json and instantly validate it against the W3C spec. Catch errors and warnings. Client‑side.
ARIA Label Checker – Online Paste HTML Search for Missing Labels
Paste HTML snippet and highlight interactive elements missing accessible labels. Quick a11y audit.
CSS Media Query Syntax Checker - Online Validator
Paste a media query and instantly check for syntax errors. See if it's correctly formed. Quick developer tool.
Twitter Card Previewer - Online See How Tweets Render
Enter a URL and fetch its Twitter card meta tags. See a live preview of how the tweet will appear. Debug social sharing.
JavaScript Syntax Validator - Online Check Errors
Paste JavaScript and catch syntax errors instantly with line numbers. Lightweight pre‑commit check. Local.
HTML Validator Lite - Online Check Syntax Errors
Paste HTML and detect unclosed tags, invalid nesting, and duplicate IDs. Lightweight client‑side validation.
WebVTT Subtitle Validator - Online Check Syntax
Paste a WebVTT file and instantly check for syntax errors. Validate timestamps and cue formatting. Essential for video devs.
HTML lang Validator - Online Check Language Tag
Validate a language tag like en‑US or zh‑Hans against the IANA registry. Ensure correct HTML lang attribute.
Robots.txt Tester - Online Check URL Allow/Disallow
Enter a URL and a user‑agent to see if it is allowed or blocked by the robots.txt file. Quick bot validation.
Semantic Versioning Validator - Online Check Semver Syntax
Validate and compare semantic version strings. Check if a version satisfies a range (e.g., ^1.2.3). Visual breakdown of major.minor.patch. Local only.
UPC Barcode Validator - Online Check Digit & EAN
Enter a UPC or EAN barcode number and validate the check digit. See if it's a real product code. Local calculation.
ARIA Attribute Validator - Online Check HTML Accessibility
Paste an HTML snippet and check for common ARIA mistakes: missing labels, invalid roles, and aria‑hidden misuse. Educate your team.
DNSSEC Chain Validator - Online Check RRSIG & DS
Validate a DNSSEC chain by entering DS and RRSIG records. Verify that signatures match. Educational. Local algorithm.
TOML Formatter & Validator - Online Config Tool
Check and beautify your TOML config files. Highlights errors and aligns tables and arrays. Safe local parsing.
.htaccess Validator - Online Check Syntax
Paste your .htaccess rules and check for common syntax errors or misconfigurations. No server required; static analysis.
DNS Record Syntax Checker - Online Validate BEFORE Publishing
Paste any DNS record and check if its format is valid for the selected record type (A, AAAA, CNAME, MX, TXT, SRV). Prevents typos.
ETag & Last‑Modified Validator - Online Check Cache Headers
Send conditional requests to a URL and verify that the server correctly handles ETag and If‑None‑Match. Audit caching.
Crypto Address Format Checker - Online Validate Wallet
Paste a Bitcoin, Ethereum, or other crypto wallet address and quickly verify its format and checksum. No connection to blockchain.
YAML Validator & Formatter - Online Check Syntax
Validate YAML syntax with line‑by‑line error messages. Also format messy YAML into clean, indented output. All in your browser.
Robots.txt Validator - Online Check Syntax & Rules
Paste a robots.txt file and validate its syntax. See if a specific user‑agent can access a path. Essential for webmasters.
Markdown Linter - Online Check Syntax & Style
Paste Markdown and get warnings for common mistakes: inconsistent heading spacing, bare URLs, and broken links. All local.
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.
Semantic Versioning Validator - Check Semver Syntax
Validate if a version string follows SemVer 2.0.0. Also sort and compare versions. Developer tool.
SQL Syntax Validator - Online Quick Check
Paste your SQL query and check for basic syntax errors. Highlights missing commas, wrong keywords. Local analysis.
Base64 String Validator - Online Check Valid Encoding
Paste a string and verify if it is valid Base64. Auto‑detects padding issues and character errors. Quick dev check.
Test Credit Card Validator - Online Luhn Check & Issuer
Paste a test card number to verify Luhn algorithm, identify issuer (Visa, MC), and check length. No real data.
PRNG Validator - Online Check Randomness Pattern
Paste a list of numbers to visually check uniformity, mean, and simple pattern analysis. Educational tool for statistics and RNG.
ISBN Validator - Online Check ISBN‑10 & ISBN‑13
Validate ISBN‑10 and ISBN‑13 numbers and compute their check digits. Useful for booksellers and libraries. All local.
XML Formatter & Validator - Free Online XML Beautifier
Easily format, validate, and beautify XML documents. Minify XML data with a single click. All processing happens locally in your browser for maximum privacy.
JSON Formatter & Validator - Online JSON Beautifier
Online JSON formatting and validation tool, supporting JSON minify/beautify, syntax highlighting, and error locating. Data processed locally in browser for security.