---
title: Next Config
description: "Wrap your Next.js config in `withConsentManifest`. An existing
  config object or function goes in as the first argument, unchanged:"
lastModified: "2026-10-10T14:59:21+01:00"
lastAuthor: Kaylee
---
Wrap your Next.js config in `withConsentManifest`. An existing config object
or function goes in as the first argument, unchanged:

```ts title="next.config.ts"
import { withConsentManifest } from 'c15t/next/build';
import type { NextConfig } from 'next';

const nextConfig = {} satisfies NextConfig;

// Reads NEXT_PUBLIC_C15T_BACKEND_URL, like defineConsentConfig.
export default withConsentManifest(nextConfig);
```

`next build`, `next dev` and `next typegen` fetch `${backendURL}/manifest` and
write the policy to `node_modules/.cache/c15t/`, outside your source tree, so
there is nothing to keep out of Git. `next start` serves the built snapshot and
fetches no policy. Without a `backendURL` option, the build reads the
`backendURL` in `c15t.config.ts`, which defaults to
`NEXT_PUBLIC_C15T_BACKEND_URL`, then `NEXT_PUBLIC_INTH_PROJECT_URL`, so saves
and the snapshot point at the same
project.

The wrapper reads `c15t.config.ts` the way Next.js reads `next.config.ts`, and
skips the fetch for `mode: hosted()`, `mode: offline()`,
`manifest({ snapshot })` and `manifest({ source: 'runtime' })`, which read no
build-time manifest. Those builds never contact the backend. If the file can't
be read at build time, for example because it imports something Node can't
load, the build warns and fetches as for `manifest()`.

The wrapper also finds `c15t.config.ts` (or `.mts`, `.js`, `.mjs`) at the
project root, next to `next.config.ts`, and points `c15t/generated` at the
cache, in Turbopack and webpack. `ConsentRoot`, `resolveConsent` and the
consent route read both without an import. Server code that needs the
snapshot itself imports `snapshot` from `c15t/generated`. Only server
bundles get the snapshot: in a browser bundle,
`c15t/generated` imports `server-only`, so importing it from a client
component fails the build. The wrapper also adds `c15t`, `@c15t/core` and
`@c15t/nextjs` to `transpilePackages`, so Pages Router server bundles see the
aliases. A package you list in `serverExternalPackages` stays external: it
reads no `c15t.config.ts` and fetches the policy at runtime.

If the fetch fails, `next build` stops. `next dev` logs a warning instead, and
`snapshot` is `undefined`, so the server fetches and caches the policy at
runtime, as with
[runtime manifest caching](/docs/frameworks/next/optimization#reuse-cached-policy-data).
To let a build continue the same way, set `onBuildError: 'runtime'`, or run it
with `C15T_ON_BUILD_ERROR=runtime`:

```ts title="next.config.ts"
export default withConsentManifest(nextConfig, { onBuildError: 'runtime' });
```

A missing backend URL counts as a failed fetch. The build skips the fetch and
leaves `snapshot` `undefined` when the backend URL is relative, or when the
config sets `output: 'export'`, which has no server to use the snapshot. With
`onBuildError: 'fail'`, a relative URL stops the build. A static export always
skips the fetch.