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GET /v1/mass-energy

E = mc²

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10 free calls per day — no sign-up, no API key. Goes through the oanor gateway.

Custom headers (optional)
api.oanor.com/relativity-api

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Code snippets

curl "https://api.oanor.com/relativity-api/v1/mass-energy" \
  -H "x-oanor-key: oanor_test_..."
await fetch("https://api.oanor.com/relativity-api/v1/mass-energy", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
$ch = curl_init("https://api.oanor.com/relativity-api/v1/mass-energy");
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$out = curl_exec($ch);
import requests
requests.get(
    "https://api.oanor.com/relativity-api/v1/mass-energy",
    headers={"x-oanor-key": "oanor_test_..."}
)

Example response

A real response from this endpoint, captured by the latest health check.

{
    "data": {
        "note": "E = mc² with c = 299,792,458 m/s. 1 kg ⇄ 8.98755×10¹⁶ J ≈ 24.97 billion kWh.",
        "inputs": {
            "source": "mass"
        },
        "mass_kg": 1,
        "energy_j": 89875517900000000,
        "energy_ev": 5.6095886e+35,
        "energy_kwh": 24965421600,
        "energy_mev": 5.6095885999999995e+29
    },
    "meta": {
        "timestamp": "2026-06-04T18:38:05.459Z",
        "request_id": "87be3687-6ee8-45b5-a9e9-ea0d88655760"
    },
    "status": "ok",
    "message": "Mass-energy",
    "success": true
}