Glossary
What is TCF string?
Also called: TC string, consent string, TCF v2.3
A TCF string, or TC string, encodes a reader's consent choices under IAB Europe's framework and travels with ad requests so each vendor can check it.
हिंदी में पढ़ेंUnder the IAB Europe Transparency and Consent Framework (TCF), a CMP records each reader’s choices as bits: 1 for yes, 0 for no. There is a bit for each numbered purpose, such as Purpose 1, storing or accessing information on a device, and for each numbered vendor; Google’s vendor ID is 755. The bits are packed into a short text string, the TC string.
Prebid and other tools attach the string to every bid request. In OpenRTB 2.6, regs.gdpr flags that GDPR applies and user.consent carries the string. Each buyer checks its own bit before it uses personal data.
TCF v2.3, released in June 2025, made a disclosedVendors segment mandatory: a second list of bits showing which vendors the banner actually showed. In v2.2, a 0 could mean the reader objected or that the vendor was never shown. The transition ended on 28 February 2026, and new strings without the segment are invalid. Google logs these as error 1.4 in Ad Manager and may default the request to limited ads.
Example
A reader says yes to Purposes 1, 3 and 4 and no to 2 and 5, so her bits for Purposes 1 to 5 read 1, 0, 1, 1, 0. If the banner showed 50 vendors, including Google (755), the disclosedVendors segment has 50 bits set to 1.
Why it matters to publishers
Without a valid string, buyers cannot use personal data and many bid less or not at all. A missing disclosedVendors segment can quietly push Google requests to limited ads.