Free Developer Tools and Practice | simpleprog

simpleprog

Tools

curl to Python Turn "Copy as cURL" into requests and httpx code, with JSON bodies, cookies, forms and auth. open tool -> robots.txt tester Check if a crawler may fetch a URL, see the exact rule that matched, and list declared sitemaps. open tool -> Subnet calculator Network, mask, wildcard, broadcast, host range and subnet splits for any IPv4 or IPv6 CIDR. open tool -> SPF & DMARC checker Explain SPF, DMARC and DKIM records, count SPF lookups against the limit and flag mistakes. open tool -> Selector & XPath tester Test CSS selectors and XPath against pasted HTML, in your browser, with Python snippets. open tool -> HTTP headers checker Redirect chain, response headers, a security-headers checklist, cookie flags and caching explained. open tool ->

Practice & reference

Cheat sheets One-page references for the commands, selectors and headers you look up again and again. open -> Practice sandbox Practice scraping safely on pages built for it, from simple HTML to tricky edge cases. open ->

Built for learning, safe to use

Each tool pairs with a lesson: the subnet calculator with Subnetting and CIDR, the robots.txt tester with robots.txt & Scraping Ethics, the SPF and DMARC checker with Email Security: SPF, DKIM and DMARC. Every result explains what it means, not just what it is.

Nothing you type is stored. The curl converter and the robots.txt and header checkers use POST so commands and URLs stay out of logs and browser history. The selector tester runs entirely in your browser. Tools that contact other servers only reach public addresses and are rate limited.