# Fathom Analytics

The c15t fathomAnalytics helper loads Fathom Analytics only after visitors allow measurement in Inth. It can also turn on Fathom route tracking for single page apps.

## Key facts

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

## Links

- [Documentation](https://c15t.com/docs/integrations/fathom-analytics)
- [Fathom Analytics](https://usefathom.com/)

Start Fathom Analytics only after visitors allow measurement. Add your site ID and turn on route tracking for single page apps.

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, c15t in that app and the site ID from your Fathom embed code. It is the data-site value.

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 Fathom

Fathom says that it sets no cookies. c15t still does not load script.js before the visitor allows measurement.

The c15t fathomAnalytics helper loads script.js with defer. It sends no consent signal to Fathom and does not call blockTrackingForMe.

If your app changes routes without a full page load, pass spa. Without it, Fathom route tracking for single page apps stays off.

## Installation

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

### Wait for permission

No request goes to Fathom until the visitor accepts measurement. On withdrawal, c15t removes the script and reloads the page.

```ts
fathomAnalytics({ site, spa })
```

An opt-out policy or no policy gives optional categories permission before a choice. Then Fathom 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 Fathom script.

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

#### Add your site ID

The helper sends the site ID as data-site. Set spa to auto, history or hash for client side routes.

```
import { fathomAnalytics } from '@c15t/integrations/fathom-analytics';

export const scripts = [fathomAnalytics({ site: 'YOUR_SITE_ID', spa: 'auto' })];
```

An empty site ID logs an error, and the script does not load.

### 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 old Fathom embed code, so the script loads only through c15t. If you already have a scripts array, add the helper to it.

## Verify your setup

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

- **Before a choice**: No request goes to cdn.usefathom.com. Click Reject and reload. There is still no request.

- **After you allow measurement**: script.js loads without a page reload. Its script element has your data-site and data-spa values.

- **After you withdraw measurement**: Save your choice. c15t reloads the page. The new page sends no request to Fathom.

Change route in your app and make sure that it sends one page view, not two. If your code calls window.fathom?.trackEvent, check measurement permission before each call.

[Open the full Fathom Analytics guide](https://c15t.com/docs/integrations/fathom-analytics)

## Related guides

- [Google Analytics](/integrations/google-analytics)

- [Matomo Analytics](/integrations/matomo-analytics)

- [OneDollarStats](/integrations/one-dollar-stats)