Error when creating alerts in amtool via cli "amtool: error: invalid character 'C' looking for beginning of value"

[aned]

./amtool  alert add alertname="foo"  --alertmanager.url http://127.0.0.1:9093
amtool: error: invalid character 'C' looking for beginning of value

./amtool --alertmanager.url=http://127.0.0.1:9093 alert add foo
amtool: error: invalid character 'C' looking for beginning of value

./amtool --version
amtool, version 0.28.1 (branch: HEAD, revision: b2099eaa2c9ebc25edb26517cb9c732738e93910)
  build user:       root@fa3ca569dfe4
  build date:       20250307-15:05:18
  go version:       go1.23.7
  platform:         linux/amd64
  tags:             netgo

[marcusboden]

I ran into that error as well. Turns out to be a HTTP/HTTPS issue hidden behind very bad error messages. I fixed it by specifying the correct url including the scheme:

amtool --alertmanager.url https://127.0.0.1:9093 alert add alertname=foo

[aned]

Thanks @marcusboden , indeed it was the issue, the error message makes no sense.