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Fathom Analytics

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.

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pnpm add @c15t/integrations
Fathom AnalyticsWaiting for consent
Before a choice

No request goes to cdn.usefathom.com. Click Reject and reload. There is still no request.

Turn the switch on, then off, to see what loads.

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

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.

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

  1. Install the integration package

    Add the helpers next to c15t. An import alone does not start the Fathom script.

    pnpm add @c15t/integrations

  2. Add your site ID

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

    src/consent-scripts.ts
    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.

  3. Register it with your existing setup

    Add scripts to the c15t configuration that you have now. Keep your Inth endpoint, mode, policy, styles and consent UI.

    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.

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

export default defineConsentConfig({ scripts });

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

    src/routes/__root.tsx
    import { scripts } from '../consent-scripts';

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

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

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

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

    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.

    app/app.config.ts
    import { scripts } from '../src/consent-scripts';

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

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

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

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

    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.

    src/c15t.client.ts
    import type { C15tClientOptionsExtension } from 'c15t/astro';
import { scripts } from './consent-scripts';

export default { scripts } satisfies C15tClientOptionsExtension;

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

    src/App.svelte
    <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>

    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.

    src/routes/+layout.svelte
    <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>

    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.

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

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

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

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

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