bknd/docs/extending/config.mdx

---
title: bknd.config.ts
---

The central configuration file to extend bknd should be placed in the root of your project, so that the [CLI](/usage/cli#using-configuration-file-bknd-config) can automatically pick it up. It allows to:
* define your database connection centrally
* pass in initial configuration or data seeds when booting the first time
* add plugins to the app
* hook into system events
* define custom routes and endpoints


A simple example of a `bknd.config.ts` file:

```typescript bknd.config.ts
import type { BkndConfig } from "bknd/adapter";

export default {
   connection: {
      url: "file:data.db",
   }
} satisfies BkndConfig;
```

## Overview

The `BkndConfig` extends the [`CreateAppConfig`](/usage/introduction#configuration-createappconfig) type with the following properties:

```typescript
export type BkndConfig = CreateAppConfig & {
   // return the app configuration as object or from a function
   app?: CreateAppConfig | ((args: Args) => CreateAppConfig);
   // called before the app is built
   beforeBuild?: (app: App) => Promise<void>;
   // called after the app has been built
   onBuilt?: (app: App) => Promise<void>;
   // passed as the first argument to the `App.build` method
   buildConfig?: Parameters<App["build"]>[0];
   // force the app to be recreated
   force?: boolean;
   // the id of the app, defaults to `app`
   id?: string;
}
```


The supported configuration file extensions are `js`, `ts`, `mjs`, `cjs` and `json`. Throughout the documentation, we'll use `ts` for the file extension.

### `app` (CreateAppConfig)
The `app` property is a function that returns a `CreateAppConfig` object. It allows to pass in the environment variables to the configuration object.

```typescript
import type { BkndConfig } from "bknd/adapter";

export default {
   app: ({ env }) => ({
      connection: {
         url: env.DB_URL,
      }
   })
} satisfies BkndConfig;
```

See [Database](/usage/database) for more information on how to configure the database connection.

### `beforeBuild`
The `beforeBuild` property is an async function that is called before the app is built. It allows to modify the app instance that may influence the build process.

```typescript
import type { BkndConfig } from "bknd/adapter";

export default {
   beforeBuild: async (app: App) => {
      // do something that has to happen before the app is built
   }
}
```

### `onBuilt`
The `onBuilt` property is an async function that is called after the app has been built. It allows to hook into the app after it has been built. This is useful for defining event listeners or register custom routes, as both the event manager and the server are recreated during the build process.

```typescript
import { type App, AppEvents } from "bknd";
import type { BkndConfig } from "bknd/adapter";

export default {
   onBuilt: async (app: App) => {
      console.log("App built", app.version());
      
      // registering an event listener
      app.emgr.onEvent(AppEvents.AppRequest, (event) => {
         console.log("Request received", event.request.url);
      })
      
      // registering a custom route
      app.server.get("/hello", (c) => c.text("Hello World"));
   }
}
```

### `force` & `id`
The `force` property is a boolean that forces the app to be recreated. This is mainly useful for serverless environments where the execution environment is re-used, and you may or may not want to recreate the app on every request.

The `id` property is the reference in a cache map. You may create multiple instances of apps in the same process by using different ids (e.g. multi tenant applications).

## Framework & Runtime configuration

Depending on which framework or runtime you're using to run bknd, the configuration object will extend the `BkndConfig` type with additional properties.

### `RuntimeBkndConfig`

[Runtime adapters](/integration/runtime) need additional configuration to serve static assets for the admin UI.

```typescript
export type RuntimeBkndConfig<Args = any> = BkndConfig<Args> & {
   // the path to the dist folder to serve static assets for the admin UI
   distPath?: string;
   // custom middleware to serve static assets for the admin UI
   serveStatic?: MiddlewareHandler | [string, MiddlewareHandler];
   // options for the admin UI
   adminOptions?: AdminControllerOptions | false;
};
```

### `FrameworkBkndConfig`

[Framework adapters](/integration/framework) may need additional configuration based on the framework's requirements. For example, the `NextjsBkndConfig` type extends the `BkndConfig` type with the following additional properties:

```typescript
type NextjsEnv = NextApiRequest["env"];
export type NextjsBkndConfig<Env = NextjsEnv> = FrameworkBkndConfig<Env> & {
   cleanRequest?: { searchParams?: string[] };
};
```

Next.js adds the mounted path to the request object, so that the `cleanRequest` property can be used to remove the mounted path from the request URL. See other frameworks for more information on how to configure them.


## Using the configuration file

The configuration file is automatically picked up if you're using the [CLI](/usage/cli). This allows interacting with your application using the `bknd` command. For example, you can run the following command in the root of your project to start an instance:

```bash
npx bknd run
```

When serving your application, you need to make sure to import the contents of your configuration file. If you're using Next.js for example, it's recommended to follow these steps:

1. create a `bknd.config.ts` file in the root of your project which defines the connection to the database, adds event listeners and custom routes.
2. create a `bknd.ts` file inside your app folder which exports helper functions to instantiate the bknd instance and retrieve the API.
3. create a catch-all route file at `src/api/[[...bknd]]/route.ts` which serves the bknd API.

This way, your application and the CLI are using the same configuration.