---
title: IAB TCF
description: Show the IAB TCF banner and dialog in a TanStack Start app for
visitors whose policy uses the IAB model, with c15t/react/iab inside
ConsentRoot.
group: frameworks
lastModified: "2026-10-10T16:01:45+01:00"
---
## 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](https://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:
```tsx title="src/components/iab-consent.tsx"
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 (
);
};
```
Render `` 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 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:
```tsx title="src/routes/__root.tsx (partial)"
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](/docs/customization/tailwind#set-up-tailwind-css-3).
## 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:
```tsx title="src/components/iab-consent.tsx"
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] },
];
```
Each restriction type has a requirement that depends on the vendor list:
|`restrictionType`|Meaning|Allowed when the vendor|
|--|--|--|
|`0`|Purpose not allowed on any legal basis|declares the purpose for consent or legitimate interest|
|`1`|Consent required|declares the purpose for legitimate interest and lists it in `flexiblePurposes`|
|`2`|Legitimate interest required|declares the purpose for consent and lists it in `flexiblePurposes`|
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](/docs/concepts/consent-state#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`.