AI engineering glossary · Web APIs HTTP
What is preflight request?
Preflight request: An automatic OPTIONS request that a browser sends before certain cross-origin calls, such as those with JSON bodies or custom headers, to ask whether the real request is allowed. The real call proceeds only if the reply permits it.
Preflight request: an example
Before a POST with an Authorization header from another site, the browser sends OPTIONS and checks the Access-Control-Allow-* headers.
Related terms
More Web APIs HTTP terms
Where you learn it
Preflight request is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.