IAB TCF

Before you turn on IAB TCF

Use IAB TCF when your ad partners require a TC String. It needs an IAB policy in your Inth project and a CMP ID. IAB Europe assigns a CMP ID to a company when it registers as a CMP (register.consensu.org/CMP). Every TC String names the CMP that wrote it, so an ID you did not register attributes your visitors' consent to someone else. Example CMP IDs in c15t demos are not production configuration.

@c15t/svelte loads the TCF add-on from @c15t/iab, which it installs as a dependency. The add-on is a separate chunk that apps without IAB never download.

Add the IAB components

Turn IAB on with the provider's iab prop, keeping your existing mode or state, scripts and other props. registeredCmpId stands for the number IAB Europe assigned to your company. The standard and IAB components add their styles automatically:

<!-- Svelte: src/App.svelte -->
<ConsentProvider mode={manifest()} {scripts} iab={{ cmpId: registeredCmpId }}>

<!-- SvelteKit: src/routes/+layout.svelte -->
<ConsentRoot state={data.consent} {scripts} iab={{ cmpId: registeredCmpId }}>

Then render IABConsentBanner and IABConsentDialog next to the standard components. The standard components cover visitors whose policy is not IAB, such as those outside Europe:

<script lang="ts">
	import {
		ConsentBanner,
		ConsentDialog,
		IABConsentBanner,
		IABConsentDialog,
	} from '@c15t/svelte';
</script>

<!-- Visitors whose policy is not IAB get the standard banner and dialog. -->
<ConsentBanner />
<ConsentDialog />
<!-- Visitors under an IAB policy get the TCF banner and preference center. -->
<IABConsentBanner />
<IABConsentDialog />

The IAB banner adds its first-paint rules before its elements render. The IAB dialog adds its rules when it opens, including the base rules it needs when rendered without a banner. Each sheet appears once per page. On a server-rendered SvelteKit page, c15tHandle writes the rendered components' rules into <head> before hydration.

To run the CSS through Tailwind CSS 3 or put it in a named cascade layer, set styles={false} on the provider and import @c15t/svelte/styles.css followed by @c15t/svelte/iab/styles.css. Stylesheets and CSS layers explains when to use that option.

Pass iab={false}, or omit it, to leave IAB off. If a visitor's policy then uses the iab model and the backend sends its vendor list, the provider throws an IABUnavailableError (code C15T_IAB_UNAVAILABLE) while rendering, on the server and in the browser: the standard banner does not handle the IAB model, so the visitor would otherwise get no working consent UI. Set iab, or remove the iab model from the policy. A backend that answers gvl: null turns IAB off for the request, and the policy runs as opt-in.

IABConsentBanner and IABConsentDialog list each component's props.

IABConsentBanner and IABConsentDialog stay hidden until an IAB policy resolves for the visitor. Forcing the dialog open does not create a policy or a vendor list, so check the policy resolution and the vendor list request before changing how they render.

Read the TCF state

getConsentManager().iab holds the live IAB state: the vendor list, purpose and vendor consents, isLoadingGVL, and the actions acceptAll(), rejectAll(), setPurposeConsent(), setVendorConsent(), setSpecialFeatureOptIn() and save(). It is null when IAB is off. getIAB() returns the same object at the moment you call it. Context getters lists every member.

For a custom IAB banner, @c15t/svelte/headless exports getIABBannerDisplayItems, processGVLData and getIABTranslations.

Restrict how vendors use a purpose

Pass publisher restrictions in the provider's iab option as publisherRestrictions, for example [{ purposeId: 4, restrictionType: 0, vendorIds: [10, 755] }] to stop vendors 10 and 755 using purpose 4. Use vendors from your own list whose declarations allow each restriction.

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.

Verify the TCF flow

Accept, reject and save purpose and vendor choices, then check in the console that __tcfapi('getTCData', 2, console.log) returns a TC String that matches what you chose. Reload and confirm it persists. Check the vendors' actual requests too; a category banner test does not show that the IAB flow works.