> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cuttlefishsync.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Using Kysely with Cuttlefish

> Set up Kysely for type-safe database queries with Cuttlefish

# Using Kysely with Cuttlefish

Learn how to use Kysely with Cuttlefish to get full type safety for your database queries.

## Prerequisites

Before starting, complete the [Quick Start](/quick-start) guide to set up Cuttlefish in your Next.js app.

## Installation

Install the Kysely packages:

```bash theme={null}
npm install @cuttlefish-sync/kysely kysely
```

## Define your database schema

Create a type definition file for your database schema. We'll create `lib/db.ts`:

```typescript theme={null}
import { Kysely } from 'kysely'

interface Database {
  todos: {
    id: number
    title: string
    completed: boolean
    created_at: Date
  }
}

// Type-only export for Cuttlefish
export type DB = Database
```

<Note>
  This is a type-only definition. You don't need to create a Kysely instance - Cuttlefish handles the database connection through the dev server.
</Note>

## Using Kysely queries

Replace raw SQL queries with Kysely's type-safe query builder using `fromKysely`:

```tsx theme={null}
'use client'

import { fromKysely } from '@cuttlefish-sync/kysely'
import { useLiveQuery } from '@cuttlefish-sync/react'
import type { DB } from '@/lib/db'

export default function Home() {
  const { data, loading, error } = useLiveQuery(
    fromKysely<DB>((db) =>
      db.selectFrom('todos')
        .selectAll()
        .orderBy('created_at', 'desc')
    )
  )

  if (loading) return <div>Loading...</div>
  if (error) return <div>Error: {error.message}</div>

  return (
    <div>
      <h1>My Todos</h1>
      <ul>
        {data?.map((todo) => (
          <li key={todo.id}>
            {todo.title} {todo.completed ? '✓' : ''}
          </li>
        ))}
      </ul>
    </div>
  )
}
```

## Type safety benefits

With Kysely, we get:

* **Autocomplete**: Your editor suggests available tables and columns
* **Type checking**: TypeScript catches typos in table/column names at compile time
* **Return type inference**: The `data` variable is automatically typed based on your query
* **Refactoring safety**: Renaming database types updates all query usages

## Next steps

* [Learn about query composition](/docs/composable-sync) - Build complex queries with type safety
* [Explore the Kysely API](https://kysely.dev) - Full Kysely documentation
* [API Reference](/docs/api/use-live-query) - Complete `useLiveQuery` reference