---
title: API Reference
description: Reference for `modifyConfig` and `onBuildComplete` in the `NextAdapter` interface.
---

## `async modifyConfig(config, context)`

Called for any CLI command that loads the `next.config.js` file to allow modification of the configuration.

**Parameters:**

- `config`: The complete Next.js configuration object
- `context.phase`: The current build phase (see [phases](/docs/app/api-reference/config/next-config-js#phase))
- `context.nextVersion`: Version of Next.js being used
- `context.projectDir`: Absolute path to the Next.js project directory

**Returns:** The modified configuration object (can be async)

## `async onBuildComplete(context)`

Called after the build process completes with detailed information about routes and outputs.

**Parameters:**

- `context.routing`: Object containing Next.js routing phases and metadata
  - `routing.beforeMiddleware`: Routes executed before middleware (includes header and redirect handling)
  - `routing.beforeFiles`: Rewrite routes checked before filesystem route matching
  - `routing.afterFiles`: Rewrite routes checked after filesystem route matching
  - `routing.dynamicRoutes`: Dynamic route matching table
  - `routing.onMatch`: Routes applied after a successful match (for example immutable static asset cache headers)
  - `routing.fallback`: Final rewrite fallback routes
  - `routing.shouldNormalizeNextData`: Whether `/_next/data/<buildId>/...` URLs should be normalized during matching
  - `routing.rsc`: Route metadata used for React Server Components routing behavior
- `context.outputs`: Detailed information about all build outputs organized by type
- `context.projectDir`: Absolute path to the Next.js project directory
- `context.repoRoot`: Absolute path to the detected repository root
- `context.distDir`: Absolute path to the build output directory
- `context.config`: The final Next.js configuration (with `modifyConfig` applied)
- `context.nextVersion`: Version of Next.js being used
- `context.buildId`: Unique identifier for the current build
