---
title: Weighted fallback
description: Choose a weighted primary transport and fail over on errors.
icon: Scale
source: "src/transports/weighted-fallback.ts"
---

Choose a weighted primary transport and fail over on errors.
Works with email, SMS, WhatsApp, and push.

<Callout title="The one rule">At least one entry with positive total weight is required.</Callout>

## Configuration

Each entry has `transport` and positive `weight`; it accepts fallback options and optional `random`.

## Quick start

<Steps>
  <Step title="Build weighted entries">

```ts
import { WeightedFallbackTransport } from "sently/transports/weighted-fallback";

const transport = new WeightedFallbackTransport([
  { transport: primary, weight: 80 },
  { transport: secondary, weight: 20 },
]);
```

  </Step>
  <Step title="Pass it to the channel sender">

```ts
const mailer = await createMailer({ transport });
// or createSmsSender / createWhatsAppSender / createPushSender
```

  </Step>
</Steps>

## Troubleshooting

<Accordions>
  <Accordion title="Does this replace the inner provider?">
    No. It delegates sends to the wrapped transports.
  </Accordion>
</Accordions>

## Next

<Cards>
  <Card title="Fallback" href="/docs/decorators/fallback" />
  <Card title="Decorators" href="/docs/decorators" />
</Cards>