Preflight Request Inspector
CORS preflight requirements: OPTIONS request with Origin + Access-Control-Request-* headers.
About this tool
Preflight Request Inspector is a single-purpose utility on instant.tw, a free toolbox of calculators, converters, generators, and quick lookups. Everything works in your browser — nothing is uploaded, nothing is stored on a server unless explicitly noted.
Category: Developer Tools — Advanced. Browse more Developer Tools — Advanced tools.