cURL

curl sends a request from the terminal and prints the response: method with -X, headers with -H, a body with -d, and -i to show the response headers. Because a curl command spells out every part of a request, it has become the standard way to share one — in documentation, bug reports and the "Copy as cURL" option of every browser's developer tools.

How it works

-d implies POST and a form content type unless you set -H "Content-Type: application/json". -L follows redirects, -v shows the whole exchange including TLS, and --fail makes curl exit non-zero on a 4xx or 5xx so it can gate a script. Single quotes around the body keep the shell from interpreting it.

The misconception

That curl and a browser send the same request. A browser adds cookies, an Origin, CORS preflights and its own User-Agent; curl sends only what you write. A call that works in curl and fails in the browser is very often a CORS or cookie problem, not an API bug.

Try it here

Every endpoint's Try it out panel generates the curl command for the request you configured, and the curl converter in the tools section turns any curl command into code in nine languages.

Related

• curl to code converter
• What CORS is

Sources

• cURL documentation

Other terms

• CORS — The browser rule that decides whether JavaScript on one origin may read a response from another.
• REST API — An API that models a system as addressable resources, manipulated with standard HTTP methods.
• API endpoint — One URL plus one HTTP method — the smallest unit of an API that a client can call.
• Query parameters — The key=value pairs after the ? in a URL, used to filter, sort, page or shape what an endpoint returns.
• Path parameters — A variable segment of a URL path, such as the 42 in /orders/42, that identifies one specific resource.
• HTTP headers — Name–value metadata sent with every request and response, separate from the body.

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Last updated 16 October 2026