How to POST and GET JSON with curl

Three pieces: -X POST for the method, -H "Content-Type: application/json" so the server parses the body as JSON, and -d for the payload:

curl -X POST https://example.com/api/users \
  -H "Content-Type: application/json" \
  -d '{"name": "Ada", "role": "admin"}'

Use single quotes around the JSON so your shell leaves the double quotes inside it alone. (Note: -d implies POST, so -X POST is technically optional — but it's good to keep it explicit.)

Modern curl has a dedicated flag that replaces the -X/-H/-d trio. --json sets Content-Type: application/json and Accept: application/json, and sends the body:

curl --json '{"name": "Ada", "role": "admin"}' https://example.com/api/users

Check your version with curl --version; if it's older than 7.82.0, use the explicit -H/-d form above.

For large or reusable payloads, put the JSON in a file and reference it with @:

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

--json @payload.json works the same way on curl 7.82.0+. Use --data-binary @file.json if you need to preserve newlines exactly (-d strips them).

To fetch JSON, ask for it with an Accept header and pipe the output to jq for readable, queryable output:

# Pretty-print the whole response
curl -s -H "Accept: application/json" https://example.com/api/users | jq

# Pull out one field
curl -s -H "Accept: application/json" https://example.com/api/users/1 | jq '.email'

-s silences the progress meter so only the JSON reaches jq.

• Forgetting Content-Type. Without it, -d defaults to application/x-www-form-urlencoded and many APIs reject the body or fail to parse it.
• Shell quoting. Double quotes inside double quotes break the payload — wrap JSON in single quotes, or read from a file.
• Getting HTML instead of JSON. If an API returns an HTML block page rather than JSON, you're being filtered as a bot — the issue is your fingerprint/IP, not your curl syntax. See the code example for routing JSON calls through a scraping API.