Free Checker tools
About Checker tools
Free tools for checking and validating inputs and pages — text diff, a regex tester, JSON validation, an OGP checker, IP lookup, WHOIS lookup, and a contrast checker. All run in your browser with no signup.
Tools tagged Checker
OGP Checker
Check Open Graph and Twitter (X) Card tags from a URL and preview the share card on X and Facebook side by side. Free, no signup.
- Checker
- SEO
IP Address Lookup
See your public IP with country / region, hostname, and your device and browser info on one page. Free, no signup, nothing to install.
- Checker
- Network
Whois Lookup
Whois lookup for up to 10 domains, URLs, or IPs — registration date, expiry, days left, nameservers, registrar, and DNSSEC. CSV download. Free, no signup.
- Checker
- Network
Contrast Checker
Check color contrast against WCAG 2.1 / 2.2 AA and AAA, with passing-color suggestions, color-blindness simulation, and APCA. Runs entirely in your browser.
- Checker
- Design & Color
- Accessibility
Text Diff Checker
Compare two texts and highlight line, word, or character-level differences. Ignore whitespace and case; copy as a unified diff. Runs entirely in your browser.
- Checker
- Development
JSON Formatter & Validator
Format, beautify, and validate JSON with your chosen indent (2/4/tab), spotting syntax errors instantly. Free and ad-free. Runs entirely in your browser.
- Edit & Format
- Checker
- Development
Regex Tester
Test JavaScript regex with live match highlighting, capture groups, replace preview, flag toggles, presets, and shareable URLs. Runs entirely in your browser.
- Checker
- Development