# Vercel Speed Insights

The c15t vercelSpeedInsights helper loads the Vercel Speed Insights collector only after visitors allow measurement in Inth. A beforeSend check drops each report while permission is off.

## Key facts

- **Tool:** Vercel Speed Insights
- **Category:** Analytics
- **Consent categories:** Measurement
- **Setup method:** c15t package
- **Package:** @c15t/integrations

## Links

- [Documentation](https://c15t.com/docs/integrations/vercel-speed-insights)
- [Vercel Speed Insights](https://vercel.com/products/speed-insights)

Collect Vercel Speed Insights Web Vitals only after visitors allow measurement. A consent check drops each report while permission is off.

Inth keeps the consent record of each choice, with the visitor’s country and the policy that applied.

[Start for free](/dashboard/sign-up)

## Before you start

You need an Inth project that connects to your app and c15t in that app. Turn on Speed Insights for the project in Vercel.

New to c15t? Complete the quickstart for your framework first. Keep its Inth endpoint, policy, styles and consent UI.

[Open the quickstart for your framework](https://c15t.com/docs/frameworks)

## How consent works with Speed Insights

Before measurement has permission, the c15t vercelSpeedInsights helper does not load the collector.

After permission, the helper defines the window.siq queue and a window.si stub. It registers a beforeSend callback and loads the script.

The collector keeps its listeners after c15t removes its script. So on withdrawal, the beforeSend callback returns null, and no report goes out. That includes the reload that c15t runs.

Reports cover only page loads after consent. The collector reads buffered paint and navigation timings, but it misses interactions before consent.

## Installation

Speed Insights has one load mode in c15t. The helper waits for measurement permission.

### Wait for permission

No request goes to Vercel until the visitor accepts measurement. On withdrawal, the helper drops each report.

```ts
vercelSpeedInsights()
```

An opt-out policy or no policy gives optional categories permission before a choice. Then Speed Insights loads on the first page. This guide uses an opt-in policy.

## Setup steps

#### Install the integration package

Add the helpers next to c15t. An import alone does not start the Speed Insights collector.

```
pnpm add @c15t/integrations
```

#### Add the helper

On Vercel, the helper needs no options. Use dsn for a deployment outside Vercel, and sampleRate to report on a share of page loads.

```
import { vercelSpeedInsights } from '@c15t/integrations/vercel-speed-insights';

export const scripts = [vercelSpeedInsights()];
```

Pass your own beforeSend through the option. A call to window.si('beforeSend', ...) replaces the consent check of the helper.

### Register it with your existing setup

#### Next.js

Add scripts to c15t.config.ts, next to next.config.ts. Keep the rest of your config, such as mode, in the same call. App Router, Pages Router and static export read the same file.

```
import { defineConsentConfig } from 'c15t/next';
import { scripts } from './src/consent-scripts';

export default defineConsentConfig({ scripts });
```

#### TanStack Start

Pass scripts to the ConsentRoot in your root route. Import helpers in the route module, not in a server function: script configurations carry callbacks.

```
import { scripts } from '../consent-scripts';

<ConsentRoot state={consent} scripts={scripts}>
```

#### React

Add scripts to the options of your ConsentProvider, next to mode. Keep the banner, dialog and preferences link inside the provider.

```
import { scripts } from './consent-scripts';

<ConsentProvider options={{ mode, scripts }}>
```

#### Nuxt

Register scripts under the c15t key in app.config.ts. Keep them out of nuxt.config.ts, which reaches the browser as JSON and drops the helper callbacks.

```
import { scripts } from '../src/consent-scripts';

export default defineAppConfig({
  c15t: { scripts },
});
```

#### Vue

Pass scripts to the c15tVue plugin call you have now. The plugin starts one script loader when the app mounts.

```
import { c15tVue, manifest } from 'c15t/vue/vue-plugin';
import { scripts } from './consent-scripts';

app.use(c15tVue, {
  mode: manifest(),
  scripts,
});
```

#### Astro

Add scripts to the client entrypoint, which the integration finds on its own. Keep helpers out of astro.config.mjs: its options are serialized into the page.

```
import type { C15tClientOptionsExtension } from 'c15t/astro';
import { scripts } from './consent-scripts';

export default { scripts } satisfies C15tClientOptionsExtension;
```

#### Svelte

Pass scripts as a prop to the ConsentProvider you have now. The provider owns the loader and disposes it on unmount.

```
<script lang="ts">
  import { ConsentProvider, manifest } from 'c15t/svelte';
  import { scripts } from './consent-scripts';
</script>

<ConsentProvider mode={manifest()} {scripts}>
  <!-- Your app and consent UI -->
</ConsentProvider>
```

#### SvelteKit

Add scripts to the ConsentRoot in the root layout. Import helpers in the layout component, not in +layout.server.ts: a server load cannot send functions to the browser.

```
<script lang="ts">
  import { ConsentRoot } from 'c15t/svelte';
  import { scripts } from '../consent-scripts';

  let { children, data } = $props();
</script>

<ConsentRoot state={data.consent} {scripts}>
  {@render children()}
</ConsentRoot>
```

#### HTML: Paste the vendor’s snippet behind consent

The helpers need a bundler. On a page with the c15t script tag, paste the vendor’s own snippet instead and keep it inert until visitors allow its category. Helper options, such as loadMode, do not apply.

```
<script type="text/plain" data-c15t-category="measurement">
  // The vendor's snippet, unchanged
</script>
```

#### JavaScript

Pass scripts to init() from @c15t/browser, next to your mode. With createConsentRuntime, pass scripts to it instead.

```
import { init, manifest } from '@c15t/browser';
import { scripts } from './consent-scripts';

const consent = init({
  mode: manifest(),
  scripts,
});
```

Remove the SpeedInsights component or the injectSpeedInsights() call from @vercel/speed-insights. The collector starts one time per page, so a copy outside c15t sends reports before consent.

## Verify your setup

Use a private window with an opt-in policy. Open DevTools Network and filter by speed-insights. Then test the three states.

- **Before a choice**: No request goes to va.vercel-scripts.com, and no POST goes to /\_vercel/speed-insights/vitals.

- **After you allow measurement**: script.js loads from va.vercel-scripts.com with data-sdkn="c15t". Change route or switch tabs, and a POST to /\_vercel/speed-insights/vitals follows.

- **After you withdraw measurement**: Save your choice. c15t reloads the page. No report goes to Vercel.

Automated browsers that set navigator.webdriver load the collector but send nothing. With debug or mode: 'development', reports show in the Console.

[Open the full Speed Insights guide](https://c15t.com/docs/integrations/vercel-speed-insights)

## Related guides

- [FullStory](/integrations/fullstory)

- [Hotjar](/integrations/hotjar)

- [LogRocket](/integrations/logrocket)