Basic curl Commands Every Web Developer Should Know

New to curl? Start with our beginner guide: Making HTTP Requests with curl

When debugging APIs or testing endpoints, you need quick, reliable tools that don’t require complex setup. While GUI tools like Postman have their place, curl commands for web developers offer unmatched speed and flexibility for command-line testing. This reference covers the essential curl commands you’ll use daily, from basic GET requests to advanced authentication patterns.

Essential curl Commands for API Testing

1. Basic GET Request

The simplest curl command fetches data from any URL:

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

This returns the raw JSON response. For better readability, pipe the output through a JSON formatter:

# macOS/Linux
curl https://api.github.com/users/octocat | jq

# Windows (requires jq installation)
curl https://api.github.com/users/octocat | jq

When to use: Quick API endpoint testing, checking if services are responding, or grabbing data for scripts.

2. POST Request with JSON Data

Modern APIs expect JSON payloads. Here’s how to send them properly:

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{"name":"John Doe","email":"john@example.com"}' \
  https://api.example.com/users

For complex JSON, save it to a file and reference it:

curl -X POST \
  -H "Content-Type: application/json" \
  -d @user-data.json \
  https://api.example.com/users

When to use: Creating resources, submitting forms, or testing POST endpoints with structured data.

3. Adding Custom Headers

APIs often require specific headers for authentication, content negotiation, or custom parameters:

curl -H "Authorization: Bearer your-token-here" \
     -H "Accept: application/json" \
     -H "User-Agent: MyApp/1.0" \
     https://api.example.com/protected-resource

When to use: API authentication, setting user agents, specifying response formats, or adding custom application headers.

4. Following Redirects

By default, curl stops at redirects. Use -L to follow them automatically:

curl -L https://bit.ly/shortened-url

Limit redirect hops to prevent infinite loops:

curl -L --max-redirs 5 https://example.com

When to use: Testing shortened URLs, following API redirects, or checking redirect chains in your applications.

5. Saving Response to File

Instead of cluttering your terminal, save responses directly to files:

# Save with original filename
curl -O https://example.com/data.json

# Save with custom filename
curl -o my-data.json https://api.example.com/export

# Save headers and body separately
curl -D headers.txt -o response.json https://api.example.com/data

When to use: Downloading files, saving API responses for analysis, or archiving test results.

6. Basic Authentication

Many APIs still use basic authentication. Handle it securely:

curl -u username:password https://api.example.com/secure-endpoint

For better security, let curl prompt for the password:

curl -u username https://api.example.com/secure-endpoint

When to use: Testing internal APIs, accessing development endpoints, or working with legacy authentication systems.

7. Verbose Output for Debugging

When requests fail or behave unexpectedly, verbose mode shows exactly what’s happening:

curl -v https://api.example.com/endpoint

This displays:

• Request headers sent
• Response headers received
• SSL/TLS handshake details
• Connection information

When to use: Debugging failed requests, understanding API behavior, or troubleshooting SSL issues.

8. Setting Timeouts

Prevent hanging requests by setting connection and total timeouts:

# 10-second connection timeout, 30-second total timeout
curl --connect-timeout 10 --max-time 30 https://slow-api.example.com

When to use: Testing slow endpoints, preventing script hangs, or working with unreliable networks.

9. Form Data Submission

For traditional form submissions or file uploads:

# Standard form data
curl -X POST -d "username=john&password=secret" https://example.com/login

# File upload
curl -F "file=@document.pdf" -F "description=Important doc" https://example.com/upload

When to use: Testing form endpoints, uploading files, or working with multipart data.

10. Including Response Headers

See both headers and body in the output:

# Include headers with response
curl -i https://api.example.com/endpoint

# Headers only (useful for checking status codes)
curl -I https://api.example.com/endpoint

When to use: Checking response codes, debugging caching issues, or examining API headers.

Advanced curl Commands for Web Developers

Working with Cookies

Maintain session state across requests:

# Save cookies to file
curl -c cookies.txt https://example.com/login

# Use saved cookies
curl -b cookies.txt https://example.com/dashboard

Proxy Configuration

Route requests through proxies for testing or security:

curl --proxy http://proxy.company.com:8080 https://api.example.com

SSL Certificate Handling

For development environments with self-signed certificates:

# Skip certificate verification (development only)
curl -k https://localhost:8443/api

# Use custom CA certificate
curl --cacert custom-ca.pem https://secure-api.example.com

Performance and Automation Tips

Batch Operations

Test multiple endpoints efficiently:

# Multiple URLs in one command
curl https://api1.example.com https://api2.example.com

# From a file
curl -K url-list.txt

Output Formatting

Make responses more readable:

# Pretty-print JSON with jq
curl -s https://api.example.com/data | jq '.'

# Extract specific fields
curl -s https://api.example.com/users | jq '.[] | .name'

Error Handling

Make curl fail silently on HTTP errors for scripting:

curl --fail --silent https://api.example.com/endpoint || echo "Request failed"

curl vs. Other Tools: When to Use What

Use curl when:

• Quick command-line testing
• Scripting and automation
• CI/CD pipeline integration
• Minimal system resource usage

Use Postman when:

• Complex request collections
• Team collaboration
• Visual response inspection
• Advanced testing workflows

Use HTTPie when:

• More readable syntax preferred
• JSON-first API testing
• Better default formatting

FAQs

Conclusion

These curl commands form the backbone of command-line API testing. Start with basic GET and POST requests, then gradually incorporate headers, authentication, and advanced features as your needs grow. The key is building muscle memory for the most common patterns—once you can quickly test endpoints from the terminal, you’ll find yourself reaching for curl constantly during development and debugging.

curl commands for web developers provide the foundation for efficient API testing and debugging. These commands work across all platforms and integrate seamlessly into development workflows, making them essential tools for any web developer’s toolkit.