Tool cluster
Developer Tools
Formatters, encoders, generators, and network diagnostics for everyday development work — organized by task, all free, no signup.
Format and validate
Encode, decode, and convert
Test and generate
Network and DNS diagnostics
- Website Uptime Checker Check whether a website is up from Instant's server with DNS status redirects response code and timing.
- Redirect chain checker Trace every HTTP redirect hop final URL status code and protocol change for a website.
- SSL Certificate Checker Check TLS certificate issuer expiry SAN domains and validity for a website.
- HTTP Header Checker Fetch response headers and highlight cache security CORS content type and server details.
- Robots.txt Tester Test whether a URL path is allowed or blocked for Googlebot Bingbot or another crawler.
- Open Graph meta debugger Fetch title description canonical Open Graph and Twitter card tags with an image preview URL.
- Broken Link Checker Crawl a page and report broken internal external and redirected links with status codes.
- DNS record lookup
- WHOIS Lookup
- IP Address Lookup
- Email Blacklist Checker Check a domain or IP against common DNSBL blocklists for mail delivery risk.
- Domain Expiry Checker Look up RDAP registration data registrar status and expiry date for a domain.
- SSL Mixed Content Checker Scan an HTTPS page for insecure HTTP images scripts styles iframes and other assets.
- Page Size / Asset Weight Checker Estimate page HTML size linked asset counts and rough script style image weight from a URL.
Preview and convert markup
How to pick the right developer tool
These run instantly in your browser — no install, no account, no rate limit. Most process your input entirely client-side, so pasted JSON, JWTs, or code snippets never leave the page.
| You want to… | Use |
|---|---|
| Pretty-print and validate JSON | JSON Formatter |
| Inspect a JWT's claims without a server round-trip | JWT Decoder |
| Check if a website is currently reachable | Website Uptime Checker |
| Follow every 301/302 hop before a page loads | Redirect Chain Checker |
| Inspect TLS expiry, issuer, and SAN names | SSL Certificate Checker |
| Preview SEO/social tags from a live URL | Open Graph Meta Debugger |
| Check a domain's DNS records at once | DNS Record Lookup |
| Build/validate a cron expression | Cron Expression Generator |
| Test a regex against sample strings | Regex Tester |