Sandbox

Use the free sandbox to build and test your integration without sending real faxes. No credit card is required.

The sandbox uses the same endpoints, request formats, and webhook events as live. Its fax records and webhook endpoints are separate from your live environment.

Make it fail on purpose

Nine test numbers produce specific outcomes, including successful delivery, busy lines, no answer, and invalid numbers. Choose a failure, adjust your error handling, and run the same test again. Other valid fax numbers simulate successful delivery.

See the test number list for each scenario.

Test billing without a charge

Your sandbox starts with virtual credits. It reserves them when you submit a fax, deducts them when delivery succeeds, and releases them when delivery fails. Adding sandbox credits does not charge a card.

The sandbox is active as soon as you register. To send real faxes, make your first credit purchase and use a live API key.

Send your first test fax

Follow the quickstart to register, verify your email, and get a sandbox API key. Send a file to +15005550001 through POST /v1/faxes to test successful delivery.

Sandbox keys start with mfx_test_. They cannot access live records or send real faxes.

Next steps

• Sandbox walkthrough: test delivery, retries, and errors.
• Sandbox and live environments: use the right key for each environment.
• Pricing: check the cost of live delivery.