🔧 cURL Command Builder
Runs entirely in your browser - no data sent to server
Output appears here...
📊 Key Data Points
-H for headers
curl -H Header-Name: value — the most important curl flag for API testing
-d for body
curl -d the body value — sets the request body, used with POST, PUT, PATCH
-v for debugging
curl -v (--verbose) prints request headers, response headers, and TLS handshake — essential for debugging authentication
curl Command Builder -- Complete USA Guide 2026
curl is the universal HTTP debugging tool — available on every platform and accepted in every tech support conversation. But writing correct curl syntax from scratch means remembering the -H header flag, -d body flag, -X method flag, and proper quoting of JSON bodies.
This builder generates curl commands from a visual request builder. Runs in your browser.
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For response analysis, pair with HTTP Headers Analyzer and HTTP Status Codes.
🔬 How This Calculator Works
Builds curl command syntax from a visual request builder. Configure: URL, HTTP method (GET/POST/PUT/PATCH/DELETE/HEAD/OPTIONS), request headers (key:value pairs), request body (raw JSON, form data, multipart), authentication (Bearer token, Basic auth, API key), query parameters, and curl flags (--verbose, --silent, --insecure, --follow-redirects).
✅ What You Can Calculate
Full HTTP method support
GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS — all HTTP methods with the correct curl -X flag syntax.
Authentication helpers
Bearer token (-H Authorization: Bearer ...), Basic auth (-u username:password), and API key header generation.
JSON body builder
Visual key-value editor for JSON request bodies. Auto-adds Content-Type: application/json header when JSON body is present.
Flag reference
Toggles for common curl flags with explanations: --verbose (debug output), --silent (suppress output), --insecure (skip SSL verification), --location (follow redirects).
🎯 Real Scenarios & Use Cases
Testing REST API endpoints
Build and test REST API calls without writing curl command syntax from memory. Copy the generated command for sharing with teammates.
Debugging authentication issues
Build a request with your auth token here and inspect the exact curl command to verify the header format matches what the API expects.
Sharing API call examples
Generate properly formatted curl commands for API documentation, bug reports, and Stack Overflow questions.
Preflight CORS debugging
Build an OPTIONS preflight request with the exact headers that your browser would send to debug CORS configuration issues.
💡 Pro Tips for Accurate Results
Always quote the URL. curl https://example.com?q=hello world fails because of the unencoded space. Use URL Encoder to encode parameters, then always wrap the URL in single quotes in curl.
-H for headers, -d for body. -H Content-Type: application/json sets a header. -d with JSON value sets the request body. For POST with JSON, always include the Content-Type header.
--verbose for debugging. curl --verbose (or -v) prints request headers, response headers, and the TLS handshake. Essential for debugging authentication and CORS issues.
Escape JSON in shell. Single-quoted JSON in curl: -d with JSON in single quotes. Double-quoted JSON needs shell escaping. Single quotes are safer for JSON.
🔗 Use These Together
🏁 Bottom Line
curl is the universal HTTP debugging tool — available on every platform and accepted in every tech support conversation. The builder handles the quoting and flag syntax so you focus on the request. For response analysis: HTTP Headers Analyzer and HTTP Status Codes.
What is curl and when do developers use it?
curl (Client URL) is a command-line tool for making HTTP requests from a terminal. Developers use it constantly for: testing API endpoints without writing code, quickly verifying that a server is responding, copying requests from browser DevTools to reproduce them in a terminal, sharing reproducible API calls in documentation and bug reports, and automating HTTP tasks in shell scripts. The output of this builder is a curl command you can paste directly into any terminal (Mac, Linux, Windows PowerShell with curl alias, or WSL).
How do I convert a browser network request to a curl command?
In Chrome or Firefox DevTools: open the Network tab, make the request, right-click on it in the network log, select Copy → Copy as cURL. This gives you the exact curl command that reproduces the request including all headers, cookies, and request body. This technique is invaluable for debugging — you can take a failing API call from a web app and run it directly in your terminal, then modify headers and body to isolate the issue without touching application code.
What are the most important curl flags to know?
-X specifies the HTTP method: -X POST, -X PUT, -X DELETE (-X GET is the default and rarely specified). -H adds a header: -H 'Content-Type: application/json'. -d specifies the request body: -d '{"key":"value"}'. -u adds Basic Auth: -u username:password (base64-encodes automatically). -k skips SSL certificate verification (for self-signed certs in development — never use in production). -v enables verbose output showing request and response headers. -o saves output to a file: -o response.json. --compressed requests compressed responses. -L follows redirects.
How do I send JSON with curl?
curl -X POST https://api.example.com/users -H 'Content-Type: application/json' -H 'Authorization: Bearer YOUR_TOKEN' -d '{"name":"Alice","email":"alice@example.com"}'. The Content-Type: application/json header tells the server to parse the body as JSON. Without it, many APIs return a 400 or 415 error. For multiline JSON, use single quotes around the body on Mac/Linux or store the JSON in a file and use -d @body.json. On Windows CMD, use double quotes around the body and escape inner quotes.
How do I authenticate API requests with curl?
Basic Auth: -u username:password (curl base64-encodes automatically) or -H 'Authorization: Basic BASE64_OF_USER_PASS'. Bearer tokens: -H 'Authorization: Bearer YOUR_JWT_OR_API_KEY'. API keys in headers: -H 'X-API-Key: YOUR_KEY'. API keys in query strings: append ?api_key=YOUR_KEY to the URL. AWS Signature V4 authentication is too complex for manual curl — use the AWS CLI or a library. OAuth 2.0 access tokens are sent as Bearer tokens after the OAuth flow completes.
How do I save a curl response to a file and check the status code?
Save response body: curl -o output.json https://api.example.com/data. Show HTTP status code only: curl -o /dev/null -s -w '%{http_code}' https://api.example.com/. Show headers and body: curl -i https://api.example.com/. Headers only: curl -I https://api.example.com/ (sends HEAD request). To check status code in a script and exit on failure: curl -f -o output.json https://api.example.com/ — the -f flag makes curl exit with status 22 on HTTP errors (4xx, 5xx), enabling if curl -f ...; then ... ; fi patterns in shell scripts.
What other API and HTTP tools are on this site?
The HTTP Headers Analyzer decodes and explains response headers from API calls. The HTTP Status Codes reference covers every status code you might see in curl output. The JWT Decoder inspects Bearer tokens used in curl Authorization headers. The Base64 Encoder encodes credentials for Basic Auth headers. The JSON Formatter beautifies JSON responses from curl. The URL Encoder handles query string encoding for complex curl URLs. All are in the Dev Tools section.