How This CORS Header Generator Works
This cors header generator turns a plain-language set of rules into the exact configuration your server needs. Fill in the origins, methods, request headers, and optional exposed headers you need, toggle credentials and set a max-age, then pick an output mode, and this cors config generator produces ready-to-use configuration for that specific target. Raw HTTP headers mode outputs the Access-Control-* headers directly, useful for any backend not covered by the other five modes. Acting as a nginx cors configuration generator and an Apache mode, both generate server-block or .htaccess configuration including the preflight OPTIONS handling. Express, FastAPI, and Django modes generate the actual code or settings block for that framework's CORS middleware or package, an express cors setup, a fastapi cors middleware example, or a django cors headers setup depending on which you pick.
Why Credentials Can't Use a Wildcard Origin
This is a real cors credentials wildcard error enforced by browsers themselves, not an arbitrary restriction this tool invented: when Access-Control-Allow-Credentials is true, a browser refuses to accept a wildcard (*) Access-Control-Allow-Origin, since that combination would let any site read authenticated responses on a user's behalf. This generator blocks that exact combination with an explicit error rather than silently producing configuration that would fail in the browser, forcing an explicit origin list (or a single specific origin) whenever credentials are enabled.
CORS Preflight Requests Explained
A cors preflight explained in one sentence: before certain cross-origin requests, the browser first sends an automatic OPTIONS request asking permission, and only sends the real request if the server's response allows it. Requests trigger a preflight when they use a method other than GET, HEAD, or POST, or set headers beyond a small safelisted set, DELETE and PUT almost always qualify, which is why this tool specifically warns when either is included in the allowed methods. The nginx and Apache modes generate explicit OPTIONS-branch handling for this, the framework modes (Express, FastAPI, Django) handle it automatically through their respective CORS middleware, no separate configuration needed.
Common Uses
Fixing a "No Access-Control-Allow-Origin header" error in the browser console, setting up an access-control-allow-origin generator pass before a frontend team starts integrating against a new API, generating framework-specific CORS code without re-deriving the exact syntax for nginx or apache cors headers htaccess configuration from memory each time, and tightening a wildcard development setup down to explicit origins before shipping to production are the most common uses of this tool. Comparing how the same origins and methods translate across nginx, Express, and Django side by side is a common secondary use when a team runs more than one backend stack.
What This Tool Doesn't Do
This tool generates configuration text, it doesn't deploy or apply it anywhere, and it doesn't validate that an origin is a well-formed URL beyond splitting the input on commas. It covers six common targets, raw headers, nginx, Apache, Express, FastAPI, and Django, not every possible framework or server. The generated Express, FastAPI, and Django snippets assume the relevant CORS package (cors, fastapi's built-in CORSMiddleware, or django-cors-headers) is already installed, this tool doesn't install anything or replace understanding how CORS actually works end to end.