Need to test your API by sending JSON data from a file? Here are the curl commands.

POST JSON File to Localhost

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d @data.json

Replace:

  • 8080 with your port
  • /api/endpoint with your API path
  • data.json with your JSON file path

The @ symbol tells curl to read from file.

PUT JSON File

Command 
curl -X PUT http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d @data.json

Same as POST, just using PUT method.

One-Liner Version

Command 
curl -X POST http://localhost:8080/api/endpoint -H "Content-Type: application/json" -d @data.json

Everything on one line.

Show Response Headers

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d @data.json \
  -i

-i includes response headers in output.

Verbose Output (Debug)

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d @data.json \
  -v

-v shows full request and response details.

With Authentication

Basic Auth:

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -u username:password \
  -d @data.json

Bearer Token:

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer your-token-here" \
  -d @data.json

API Key:

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -H "X-API-Key: your-api-key" \
  -d @data.json

Send Inline JSON (No File)

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d '{"key":"value","number":123}'

Single quotes prevent shell interpretation.

File in Different Directory

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d @/path/to/data.json

Use absolute or relative path.

Save Response to File

Command 
curl -X POST http://localhost:8080/api/endpoint \
  -H "Content-Type: application/json" \
  -d @data.json \
  -o response.json

Response saved to response.json.

Common Localhost Ports

  • 3000: Node.js, React dev servers
  • 8000: Python HTTP server, Django
  • 8080: Common Java, general dev
  • 5000: Flask default
  • 4200: Angular dev server
  • 3001: Alternative Node.js

Troubleshooting

"Failed to connect" error:

  • API not running
  • Wrong port number
  • Check http:// vs https://

"curl: no such file" error:

  • JSON file doesn't exist
  • Wrong file path
  • Check current directory with pwd

Unexpected response:

  • Check JSON syntax with cat data.json
  • Validate JSON at jsonlint.com
  • Use -v flag to see full request

Example JSON File

Create data.json:

Command 
{
  "name": "Test User",
  "email": "test@example.com",
  "active": true,
  "roles": ["admin", "user"]
}

Then run:

Command 
curl -X POST http://localhost:8080/users -H "Content-Type: application/json" -d @data.json

Bottom Line

Basic POST command:

Command 
curl -X POST http://localhost:8080/api/endpoint -H "Content-Type: application/json" -d @data.json

The @ symbol reads from file. Change POST to PUT for PUT requests. Add -v for debugging. Add -i for response headers.

Works with any localhost API during development.