Curl Verbose Example

The command

curl -v https://httpbin.org/get

Flags that show more, or less

The three kinds of line

Every line of verbose output starts with a marker. An asterisk is curl talking about itself: the address it resolved, the connection it opened, the TLS version and certificate it negotiated, whether it reused a connection. A greater-than sign is a header line curl sent. A less-than sign is a header line it received. Lines with no marker are the response body, which is not part of the verbose output at all and is simply being printed as usual.

Read them in that order when something fails. If the asterisk lines stop early, the problem is the network or TLS and no request was ever sent. If the request lines are not what you intended, the problem is your command: a header missing, a method changed by a flag. If both look right, the answer is in the response headers.

$ curl -v https://example.com/
* Host example.com:443 was resolved.
*   Trying 203.0.113.10:443...
* Connected to example.com (203.0.113.10) port 443
* SSL connection using TLSv1.3 / TLS_AES_256_GCM_SHA384
* Server certificate:
*  subject: CN=example.com
*  expire date: ...
*  SSL certificate verify ok.
> GET / HTTP/2
> Host: example.com
> User-Agent: curl/8.5.0
> Accept: */*
>
< HTTP/2 200
< content-type: text/html; charset=UTF-8
< content-length: 1256
<
<!doctype html>
...

Verbose output goes to stderr

Curl writes the body to standard output and the verbose lines to standard error. That split is what lets you pipe the body into another program with -v switched on and not corrupt it. It is also why curl -v … | grep appears to find nothing: the pipe carries only stdout. Merge the two streams with 2>&1 to search the verbose text, or point stderr at a file to keep a log beside the normal output.

# only the header lines, sent and received
curl -sS -o /dev/null -v https://httpbin.org/get 2>&1 | grep -E '^[<>]'

# keep the body on screen, save the conversation
curl -v https://httpbin.org/get 2> verbose.log

When you only want the headers or the status

Verbose mode is more than you need for the commonest question, which is what the server answered. -i prints the status line and response headers above the body. -D - with the body discarded gives the response headers of a real GET, which can differ from what a HEAD request returns. And a -w format prints the status code alone, which is the form to use in a script.

curl -i https://httpbin.org/status/204
curl -sS -D - -o /dev/null https://httpbin.org/get
curl -sS -o /dev/null -w '%{http_code}\n' https://httpbin.org/status/404

Seeing the request body: --trace-ascii

-v shows the headers curl sent and never the body it sent after them. When the question is whether your JSON left the machine intact, or what a -d value looked like after the shell had finished with it, use --trace-ascii. It logs every byte in both directions with a line saying which direction and how many bytes. Give it a file name, or a dash to print to the terminal. --trace-time adds a timestamp to each line, which shows where a slow request spends its time: a gap before the first received header is the server working, a gap before the connection line is the network.

curl --trace-ascii - -H 'Content-Type: application/json' -d '{"name":"Ada"}' https://httpbin.org/post

curl -v --trace-time https://httpbin.org/delay/1

Timing without the noise

For numbers instead of a log, -w reports how long each phase took, as seconds counted from the start of the request. Subtract neighbouring values to get the length of a phase: the TLS handshake is the difference between the connect and appconnect figures.

curl -sS -o /dev/null https://httpbin.org/get \
  -w 'dns %{time_namelookup}  tcp %{time_connect}  tls %{time_appconnect}  first byte %{time_starttransfer}  total %{time_total}\n'

Common mistakes

• Verbose output contains your credentials. The Authorization header and cookies you sent are among the request lines. Remove them before pasting a log into a ticket or a chat.
• Expecting the request body in -v. It is not there. Use --trace-ascii.
• Combining -v with --trace. They are alternatives; curl uses one and warns about the other.
• Reading HTTP/2 output with HTTP/1.1 expectations. Header names are lower case and the status line has no reason phrase: < HTTP/2 200, not 200 OK.
• Using -s alone in a script. It hides error messages as well as the progress meter, so a failure prints nothing. Write -sS.

Related curl examples

More under Network behaviour

• Curl Follow Redirect Example
• Curl Proxy Server Example
• Curl Download File Example
• Curl CORS Request Example

References

• curl man page: -v — Verbose mode and the meaning of its line prefixes.
• curl man page: --trace-ascii — A full trace of sent and received data, as text.
• curl man page: --trace-time — Timestamps on verbose and trace output.
• curl man page: -w — Every --write-out variable, including status code and timings.

These links leave api-tester.com, which is independent of the projects they point to.

FAQ