curl — The Command Line Tool for Transferring Data with URLs

What it is

curl is a command-line tool and library (libcurl) for transferring data with URL syntax. It supports HTTP, HTTPS, FTP, SFTP, and over 25 other protocols. curl is installed on billions of devices and is the de facto standard for making HTTP requests from the command line and from applications via libcurl.

Developers, sysadmins, and anyone who interacts with APIs or web services uses curl daily. It is the standard tool for testing endpoints, downloading files, and scripting HTTP interactions in shell scripts and CI/CD pipelines.

How it saves time or tokens

curl is a single binary with no dependencies that works identically across Linux, macOS, and Windows. One curl command replaces writing HTTP client code in any programming language. For API testing and debugging, curl commands are shareable, reproducible, and can be directly pasted from documentation.

How to use

1. Make a basic GET request:

curl https://api.github.com/users/octocat

1. POST JSON data:

curl -X POST https://httpbin.org/post \
  -H 'Content-Type: application/json' \
  -d '{"name": "test", "value": 42}'

1. Download a file with progress:

curl -L -O https://example.com/file.tar.gz

Example

# Send a request with bearer token auth
curl -s https://api.example.com/data \
  -H 'Authorization: Bearer sk-your-token' \
  -H 'Accept: application/json' | python3 -m json.tool

# Upload a file with multipart form data
curl -X POST https://api.example.com/upload \
  -F 'file=@document.pdf' \
  -F 'description=Q1 report'

# Follow redirects and save cookies
curl -L -c cookies.txt -b cookies.txt https://example.com/login

Related on TokRepo

• AI tools for API — API development and testing tools
• AI tools for automation — Command-line automation tools

Common pitfalls

• Forgetting -L to follow redirects. Many URLs return 301/302 redirects, and without -L curl stops at the redirect response.
• Not quoting URLs with special characters. Ampersands, brackets, and query strings need proper quoting or escaping in shell environments.
• Using -k to skip certificate verification in production scripts. This disables TLS security and should only be used for local development.