Generate the JSON key in Firebase Console
- Open your Firebase project.
- Open Project settings.
- Select Service accounts.
- Use the Firebase Admin SDK section to generate a new private key for an account you are authorized to use.
- Store the downloaded JSON file securely.
What the file contains
The JSON includes fields such as project_id, client_email, and private_key. The private key is sensitive because it can be used to create signed assertions for that service account.
Use it in the FCM tester
On the FCM notification tester, select the JSON file or paste its contents. The tool reads the project ID and signing credentials, obtains a short-lived OAuth token, and sends the notification through FCM HTTP v1.
Security practices
Prefer least-privilege credentials, do not commit the JSON to Git, do not share it publicly, and rotate the key if exposure is suspected. For production applications, use stronger workload identity mechanisms when they are available instead of distributing long-lived private keys.
Read Google Cloud's service account key security guidance for additional controls.