Prebid.js

Prebid.js is a free, open-source JavaScript library, maintained by Prebid.org, that runs header bidding auctions inside a web page by collecting bids from many demand partners before the page calls its ad server.

Prebid.js is the header bidding wrapper most publishers know by name. When a page loads, it holds the ad server tag on a timer and asks the SSPs and exchanges the publisher has chosen for bids. It then hands the bids, prices included, to the ad server as key-values. If the ad server picks a Prebid line item, Prebid.js writes the winning creative into the slot (Prebid.org, accessed 9 November 2026).

The library has a small core and many plug-ins. Bidder adapters translate the request for each demand partner. Analytics adapters report latency, bid rates and revenue. Modules add price floors, consent handling, user ID systems and more. Prebid.org says the project counts more than 300 demand sources and 50 analytics adapters (same page).

Each publisher compiles its own build with only the modules it needs, which keeps the file small. Releases are frequent: version 11.47.0 shipped on 4 November 2026 (GitHub, Prebid.js releases). For apps and server-side auctions, the same project maintains Prebid Server and Prebid Mobile.

Example: On 9 November 2026 the Prebid.js modules folder held more than 530 files ending in BidAdapter.js or BidAdapter.ts, by our count (GitHub, Prebid.js modules folder). A publisher that works with six SSPs builds a package with those six adapters plus the floors and consent modules, and leaves the other 532 out.

Related terms: header bidding, header bidding wrapper, bidder adapter, Prebid Server, timeout, ad server.

Authoritative source: Prebid.org, "About Prebid.js for Header Bidding" (accessed 9 November 2026).

Read the full guide: Prebid.js guide: events, bidder adapters, releases and debugging.