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SenderKit runs in two modes — test and live — so you can wire up and exercise sends without risking a real notification to a real person. You don’t configure an environment in code or pass a flag; the mode is decided by which API key you use.

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Test vs live

The key prefix selects the mode:
  • sk_test_ — test mode. SenderKit never calls your providers. It accepts the send, renders the template, and synthesizes a realistic delivery lifecycle so your logs and dashboards look exactly like production — but nothing reaches a real inbox, phone, or device.
  • sk_live_ — live mode. Sends are delivered for real through your connected providers.
The prefix is only a hint for humans; SenderKit derives the mode from the key server-side, so the same code path behaves correctly just by swapping the key. See Authentication for how keys are created and managed.
Messages are isolated by mode — test sends and live sends are separate records, and listing messages returns only those for the key’s mode.

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How a version reaches live

There’s no separate staging tier to promote through. You iterate in test mode (which renders your latest draft) and, when it’s ready, publish the version — that’s what makes it live. Publishing is the gate between the two modes.
Test keys never call your providers, so you won’t receive a real email, SMS, or push in test mode — that’s by design. Switch to an sk_live_ key to send for real.

Versioning

How publishing chooses the live version.

Authentication

Creating and rotating test and live keys.