About

Responsive Breakpoint Tester lets you preview any public web page across multiple viewport widths at once. It focuses on: • Speed – minimal overhead + lazy iframe loading. • Shareability – copy a single URL to reproduce breakpoints and settings. • Local privacy – everything (presets, theme) stored in your browser. Limitations: Some sites set security headers (X-Frame-Options / frame-ancestors) that block embedding. Those frames will show as blocked. This is a browser security policy – not a bug in the tool.