curl --request POST \
  --url https://api.iotools.cloud/v1/tool/wavelength-frequency-calculator \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "inputMode": "wavelength",
  "wavelength": "550",
  "wavelengthUnit": "1e-9"
}
'

{
  "tool": "wavelength-frequency-calculator",
  "tool_version": "1.0.1",
  "outputs": {
    "summary": "550 nm ↔ 545.1 THz",
    "results": [
      {
        "property": "Spectrum band",
        "value": "Visible"
      },
      {
        "property": "Wavelength",
        "value": "550 nm"
      },
      {
        "property": "Frequency",
        "value": "545.1 THz"
      },
      {
        "property": "Photon energy",
        "value": "2.254 eV"
      },
      {
        "property": "Photon energy (joules)",
        "value": "3.6117e-19 J"
      },
      {
        "property": "Approx. visible colour",
        "value": "rgb(163,255,0)"
      }
    ]
  },
  "credits_used": 3,
  "credits_remaining": null
}