If you’re working with APIs, learning how to send POST requests using cURL is a must. It’s one of the most straightforward ways to test endpoints, upload data, or interact with servers — all from your terminal.
In this post, we’ll show you how to send POST requests using cURL, including how to send JSON, XML, files, form data, and more.
Step 1: Is cURL Installed?
Most systems already have cURL. To check, run:
curl --version
If it’s not installed, grab it from curl.se. Windows users may need Git Bash or WSL for best results.
Step 2: A Simple POST Request
Here’s the most basic example of a POST request using cURL:
curl -X POST -d "Hello" https://example.com/api
-X POST= HTTP method-d= data you’re sending in the body
Step 3: Add Content-Type Headers
To tell the server what kind of data you’re sending, include a Content-Type header:
For plain text:
curl -X POST -H "Content-Type: text/plain" -d "Hello" https://example.com/api
For JSON:
curl -X POST -H "Content-Type: application/json" \
-d '{"name":"Alice","age":30}' https://example.com/api
Use single quotes to wrap JSON so your terminal doesn’t get confused by inner double quotes.
Step 4: Send XML Payloads
If the API expects XML:
curl -X POST -H "Content-Type: application/xml" \
-d '<?xml version="1.0"?><user><name>Alice</name></user>' \
https://example.com/api
Step 5: Upload Files with -F
To upload files (like images, documents, or logs):
curl -X POST -F "file=@/path/to/file.jpg" https://example.com/upload
Upload multiple files:
curl -X POST \
-F "image1=@/path/to/one.jpg" \
-F "image2=@/path/to/two.jpg" \
https://example.com/upload
cURL automatically handles multipart/form-data for you.
Step 6: Send Form Data
For classic form-style submissions (like logging in or submitting a contact form):
curl -X POST -d "username=test&password=1234" https://example.com/login
You can also pass multiple form fields with repeated -d flags or combine them into one string.
Step 7: Add Basic Authentication
If the endpoint requires login credentials, use -u:
curl -u username:password https://example.com/secure
This adds an Authorisation header automatically using Base64 encoding.
Bonus: Using cURL with Proxies
If you’re testing geo-targeted endpoints or want extra privacy, you can use cURL with a proxy like this:
curl -x http://proxyuser:proxypass@proxy.thunderproxy.com:port \
-X POST -d '{"action":"test"}' https://example.com/api
At Thunderproxy.com, we provide residential proxies that work perfectly with cURL. This is especially helpful when testing from different locations or bypassing rate limits.
Final Thoughts
cURL is a go-to tool for developers, sysadmins, and testers. It’s fast, lightweight, and gets the job done — whether you’re sending JSON, uploading files, or logging into protected endpoints.
Once you learn the basic flags (-X, -d, -H, -F, -u), you’ll be comfortable crafting any kind of HTTP request in seconds.