IAB TCF

Before you start

Use the IAB integration when your site needs the Transparency and Consent Framework. Enable IAB in your Inth project and give a policy the iab model. You also need a CMP ID, which IAB Europe assigns when a company registers as a CMP at register.consensu.org/CMP. Every TC String names the CMP that wrote it, so do not use an ID you did not register.

The IAB components ship with the c15t package; no extra install is needed. With the quickstart's root loader, the server resolves IAB visitors like any other visitor, and the policy manifest carries the vendor list reference.

Render the IAB banner and dialog

The stock ConsentBanner and ConsentDialog stay closed under the iab model. Render the IAB components inside ConsentRoot, next to them:

import {
	IABConsentBanner,
	IABConsentDialog,
	IABProvider,
} from 'c15t/react/iab';
import { useModel } from 'c15t/tanstack-start';

export const IABConsent = ({ cmpId }: { cmpId: number }) => {
	const model = useModel();
	if (model !== 'iab') {
		return null;
	}
	return (
		<IABProvider cmpId={cmpId}>
			<IABConsentBanner />
			<IABConsentDialog />
		</IABProvider>
	);
};

Render <IABConsent cmpId={YOUR_CMP_ID} /> in the root route, next to ConsentBanner. Checking useModel() renders the IAB components only for visitors whose policy uses the IAB model.

The IAB banner and dialog render their own styles by default. Leave ConsentRoot's styles option enabled. The banner's styles render in the server HTML, and the dialog loads its rules when opened.

Supply the CMP ID from your deployment's IAB configuration. Keep a persistent preferences entry point through the surrounding consent provider.

Resolve the policy before rendering

IAB components remain hidden until an applicable policy resolves. Forcing a dialog open does not create a policy or vendor list. Inspect resolution and the Global Vendor List response before changing rendering conditions.

IAB presentation follows presentation.prompt.blocking and presentation.preferences.blocking. A blocking dialog needs focus management, scroll locking and a backdrop together.

Mount IABProvider for every IAB policy

IAB is opt-in. The standard ConsentBanner and ConsentDialog do not handle the IAB model, so when a visitor's policy uses it, the backend sends its vendor list and the app has no IABProvider, they throw an IABUnavailableError (code C15T_IAB_UNAVAILABLE): c15t: this visitor's policy uses IAB TCF, but no <IABProvider> is mounted. The error happens during render, on the server and in the browser, so your error boundary or the framework's error overlay shows it. Render IABProvider from c15t/react/iab for those visitors, or remove the iab model from the policy.

Verify vendor and purpose choices

Test category choices alongside vendor, purpose, legitimate-interest and special feature controls used by your integration. Confirm the TC String and __tcfapi reflect the saved state, and verify the vendor's actual requests. A category-only banner test does not establish that the IAB flow works.

Load an external stylesheet

With Tailwind CSS 3, or when you want to put c15t in a named cascade layer, link the base stylesheet and then the IAB stylesheet in the root route's head(). The IAB stylesheet holds the IAB rules and uses the base stylesheet's tokens. Set styles: false in ConsentRoot's options so the components use those stylesheets:

import consentCss from 'c15t/tanstack-start/styles.css?url';
import iabCss from 'c15t/tanstack-start/iab/styles.css?url';

// In head().links:
{ href: consentCss, rel: 'stylesheet' },
{ href: iabCss, rel: 'stylesheet' },

// On ConsentRoot:
options={{ styles: false }}

Tailwind CSS 3 also needs the PostCSS plugin.

Restrict how vendors use a purpose

Publisher restrictions override a vendor's declared use of one purpose. Pass them to IABProvider as publisherRestrictions. The vendor IDs below are placeholders; use vendors from your list whose declarations allow each restriction:

const publisherRestrictions = [
  // Vendors 10 and 755 may not use purpose 4.
  { purposeId: 4, restrictionType: 0 as const, vendorIds: [10, 755] },
  // Vendor 755 must use legitimate interest for purpose 7.
  { purposeId: 7, restrictionType: 2 as const, vendorIds: [755] },
];

<IABProvider cmpId={cmpId} publisherRestrictions={publisherRestrictions}>

Each restriction type has a requirement that depends on the vendor list:

Type 2 is never allowed for purposes 1, 3, 4, 5 and 6, which TCF allows only with consent. TCF allows restrictions only in service-specific TC strings. c15t always writes those, so the deprecated isServiceSpecific option has no effect on restrictions. c15t copies the restrictions when the CMP starts, so changing your array afterwards has no effect.

c15t checks restrictions when the vendor list loads and again before each TC String is encoded. Unsupported restrictions include type 3, which the spec reserves, a vendor or purpose missing from the list, and a vendor with two restriction types for one purpose. They are never dropped. Loading IAB settings, saving and generating a TC String all reject with a PublisherRestrictionError exported by @c15t/iab. On a createIAB handle these are whenReady(), save() and generateTCString(). No TC String is written and no consent is recorded. Retrying whenReady() does not fetch another vendor list. The error lasts until a new vendor list is set up: with an explicit gvl option that never happens, so saving keeps failing even if the kernel later holds a different list. When the CMP follows the kernel's list instead, a replacement list is checked again and saving works once it accepts the restrictions. When a replacement vendor list makes a restriction unsupported, c15t also clears the TC authority confirmed under the previous list, so gated scripts stop until the configuration is fixed. Whenever c15t withdraws the authority it confirmed, it also removes the TC String from the euconsent-v2 cookie and localStorage entry. Because the check reads the current vendor list, a vendor that stops declaring a purpose or its flexibility makes a restriction invalid. Narrow a vendors allowlist and your restrictions together.

Saved TC Strings carry the restrictions in their PubRestrictions section, and __tcfapi('getTCData') reports them as publisher.restrictions, keyed by purpose ID, then vendor ID. A stored TC String whose restrictions differ from the current configuration is not restored. If the visitor's stored choice is otherwise current, the banner opens again, as it does after a policy change, and closes once the visitor saves. IAB gates that depend on the TC String stay denied until then. c15t also removes the superseded TC String from the euconsent-v2 cookie and localStorage entry, so vendors reading standard storage do not pick it up. An unchanged configuration restores the stored TC String without asking. When reading a string written under TCF policy version 2 or 3, c15t accepts type 2 for purposes 3 to 6, which those versions allowed. Strings c15t writes always follow the current policy.

The React, Vue, Svelte and @c15t/browser/iab preference centres list each vendor under the legal basis the restrictions leave it. A vendor whose purpose now requires legitimate interest gets an objection control instead of a consent toggle, and a prohibited purpose no longer lists the vendor. A purpose whose vendors all use legitimate interest has no consent switch, because turning one off would change nothing the vendors rely on; its objection control is the opt-out. Such a purpose does not decide its c15t category: the category follows the purposes in it that the visitor can consent to. Legitimate interest never grants a category on its own. If none of a category's purposes has a consent basis, nothing can consent to them, Accept All included, so the category stays denied. See categories under an IAB policy. Stack switches cover only the purposes some vendor processes on consent. Display-model rows expose this as hasConsentBasis. Custom preference UIs can call applyPublisherRestrictionsToGVL from @c15t/iab/headless, or pass publisherRestrictions to processGVLForDialog, to get the same vendor declarations. The configured restrictions are on the kernel's IAB state as publisherRestrictions.

Consent-gated scripts, network rules and iframes with a vendorId also apply the confirmed restrictions for that vendor:

• Type 0 blocks a target that declares the purpose in iabPurposes or iabLegIntPurposes.
• Type 1 makes a purpose declared in iabLegIntPurposes require purpose and vendor consent. Legitimate interest no longer satisfies it.
• Type 2 makes a purpose declared in iabPurposes require purpose and vendor legitimate interest. Consent no longer satisfies it.

Types 1 and 2 block the target when the vendor list does not mark the purpose as flexible for that vendor. Targets without a vendorId ignore restrictions. A target that uses only legitimate interest once restrictions apply is not blocked by a refused category, since it needs no consent; its legitimate interest signals and the visitor's objection decide. GPC and strict scope still block it, and the category stays refused for scripts that depend on it. Accept All grants the vendor signal a restriction moves a purpose to, including legitimate interest for a vendor that declares none. Legitimate interest a restriction introduces applies until the visitor objects: the preference centres show it as allowed, and saving without touching it encodes it as allowed. introducedLegitimateInterest from @c15t/iab/headless lists those purposes and vendors for custom preference UIs.

How the preference centre shows features

The stock IAB preference centres in React, Next.js, Vue, Svelte, Astro and the script tag follow TCF 2.4 and Policies v5.0.b. Special purposes stay in their locked section with a lock icon, because the visitor cannot object to them.

Features get their own section after the special purposes. It shows the IAB standard text for features from the Global Vendor List's standardTexts.features. If the list has no standard text, it shows the iab.preferenceCenter.features.description translation. Each feature lists its name, description, illustrations and the vendors that use it. The section has no switch, lock or vendor toggle, because TCF forbids showing features next to a control that cannot be disabled.

The feature section follows the theme's spacing and typography tokens. Its disclosure arrows are decorative and stay out of the accessibility tree.

A custom preference UI gets the same rows from resolveIABDialogDisplayModel in @c15t/iab/headless. essentialRows holds the special purposes only. featureRows holds the features, with locked: false and toggle: 'none', so render them without a control. featuresStandardText is the standard text, or null when you should use the translation.

Each vendor's privacy policy and legitimate interest links come from its urls[] entry in the Global Vendor List. The stock preference centres pick the entry for the language the banner shows, then English. A custom UI gets the same links from resolveIABVendorUrls(vendor, language) in @c15t/iab/headless, or from policyUrl and legitimateInterestUrl on the vendors processGVLForDialog returns when you pass it language. Vendor lists older than GVL v3 have a single policyUrl field, which c15t still reads.

Consent scope

c15t stores TCF choices per site and browser, which the TCF calls service-specific scope. It does not sync TC strings across devices, and every TC string it writes has IsServiceSpecific set to 1.

Do not use /consent/check or your own account data to skip the TCF banner on another device. That turns the choice into multi-device scope, which the TCF requires you to disclose in the first layer, and c15t does not show that disclosure. The isServiceSpecific option is deprecated. c15t ignores it and logs a warning when you pass false.