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Add a cookie consent banner to Svelte

c15t puts the banner in your Svelte app as code. It holds tags until the visitor chooses and keeps Google Consent Mode v2 in sync.

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Sample Consent banner with c15t’s English strings

Install c15t in a Svelte app

c15t is the open source consent library behind Inth Consent. It renders the banner from your own bundle and records each choice in your Inth project.

npm install c15t @c15t/integrations

The c15t package gives you the Svelte components from c15t/svelte and the Vite plugin from c15t/svelte/vite.

Add your Inth project URL to .env. Copy it from your Inth dashboard. Vite reads it at build time, so set it before you build.

.env

VITE_C15T_BACKEND_URL=https://your-project.inth.app

Add consentManifest to the plugins in vite.config.ts. It gives the backend URL to hosted() and writes no file into your project.

vite.config.ts

import { svelte } from '@sveltejs/vite-plugin-svelte';
import { consentManifest } from 'c15t/svelte/vite';
import { defineConfig } from 'vite';

export default defineConfig({ plugins: [consentManifest(), svelte()] });

Code on this page comes from the c15t Svelte quickstart, checked 28 October 2026.

Do you use SvelteKit? See the SvelteKit cookie consent banner. It puts the banner in the server HTML.

Mount the provider in App.svelte

Render ConsentProvider around your app, with the vendor scripts that c15t loads. The provider starts consent when it mounts, so keep it at the root of the app.

src/App.svelte

<script lang="ts">
  import { posthog } from '@c15t/integrations/posthog';
  import {
    ConsentBanner,
    ConsentDialog,
    ConsentDialogLink,
    ConsentProvider,
    hosted,
  } from 'c15t/svelte';

  const scripts = [
    posthog({
      id: 'phc_your_project_key',
      initOptions: { cookieless_mode: 'never' },
      loadMode: 'after-consent',
    }),
  ];
</script>

<ConsentProvider mode={hosted()} {scripts}>
  <main>
    <h1>c15t + Svelte</h1>
    <p>Your app goes here.</p>
  </main>
  <footer>
    <ConsentDialogLink>Privacy settings</ConsentDialogLink>
  </footer>
  <ConsentBanner />
  <ConsentDialog />
</ConsentProvider>

ConsentDialog loads in its own chunk after the page. ConsentDialogLink lets visitors open their preferences again, so put it in the footer. There is no stylesheet to import.

Hold scripts until consent

With loadMode: 'after-consent', PostHog waits for measurement permission. Remove any <script> tags or SDK imports that already load PostHog, so c15t is the only thing that loads it.

Svelte scripts and embeds covers more vendors, iframes and the network blocker. The c15t integrations list the helper for each vendor.

src/consent-scripts.ts

import { gtag } from '@c15t/integrations/google-tag';

export const scripts = [gtag({ id: 'G-XXXXXXXXXX', category: 'measurement' })];

Show the right banner in each region

Your Inth project sets a policy for each region, such as opt in for the EU and UK or opt out for California. With hosted(), the browser asks your backend for the policy, and the backend reads the visitor’s location from that request. Regional policies need no extra code.

Test each region before launch. See how regional policies work.

When the banner appears

The browser resolves consent after the page loads, so the banner appears after the first paint. consentManifest() adds a small script to index.html that sends /init while your JavaScript downloads.

For a banner in the server HTML, use SvelteKit. Measure your own pages before and after you add the banner.

Check that consent gates work

Build with vite build, run vite preview and open a private window with the Network tab open. Test under an opt in policy, such as the EU policy.

  1. Under an opt in policy, no PostHog request leaves the page before a choice.
  2. After Reject All and a reload, PostHog stays off.
  3. When you turn on measurement in Privacy settings, PostHog loads.
  4. When you turn measurement off, the page reloads without PostHog.

Choices post to your Inth project. Check that Inth has a record for each one. The c15t verify consent guide has the full release checklist.

Use Inth in production

c15t is open source. Point it at your Inth project, which hosts the backend and keeps the consent records. See Inth open source.

c15t also has a local mode with no backend. It keeps no consent records, so the docs advise against it in production.

Want to see what else your repo sends before consent? Run a free codebase scan.

Cookie consent banners for other frameworks

The same banner and the same Inth project work in other stacks. See the setup for Next.js, React, TanStack Start, Nuxt, Vue, Astro, SvelteKit, HTML and JavaScript.

See how the Inth consent banner works.

Questions about Svelte consent