What is a Bid Request / Bid Response?
Bid requests and bid responses form the two-part handshake at the heart of programmatic advertising. When a user visits a website or app, the publisher's ad server generates a bid request – a message containing details about the available ad impression and the user. This request is sent to an ad exchange or demand-side platform (DSP), which forwards it to multiple advertisers and agencies simultaneously.
Advertisers evaluate the bid request in milliseconds and respond with a bid response – their offer to purchase that impression at a specific price, along with the creative ad they wish to display. The ad exchange then selects the highest bid and serves the winning ad.
Why It Matters
This automated auction system is what makes programmatic buying efficient and scalable. Rather than manually negotiating individual ad placements, UK agencies can reach thousands of relevant users daily through algorithmic bidding. It also provides transparency: you only pay for impressions that meet your targeting criteria, and you see real-time data on what you're bidding on.
For media buyers, understanding bid mechanics is essential for optimising campaigns. Your bid price directly influences win rate and cost per acquisition, while bid response data reveals which placements and audiences are most valuable to your campaigns.
When It's Used
Bid requests and responses occur continuously across display, video, and mobile advertising channels. They're the backbone of real-time bidding (RTB) on ad exchanges like Google Ad Exchange, Rubicon Project, and others commonly used in the UK market. When you run a programmatic campaign through a DSP – whether that's The Trade Desk, DV360, or similar platforms – you're leveraging bid request/response technology thousands of times per day.
Key Technical Details
Bid requests typically follow the OpenRTB specification, an industry standard that ensures compatibility between exchanges and buyers. They include:
- User identifiers and cookie data
- Device and browser information
- Page context and site category
- Available ad slots (size, position)
- Floor price (minimum acceptable bid)
Your DSP's algorithms use this data to make split-second decisions about whether to bid and how much to offer. Bid response latency must be under 100ms to avoid timing out and losing the impression.
Best Practices
For UK agencies, monitor your bid win rate and average bid price in your DSP dashboards. High bid prices with low conversions suggest you're overpaying for weak audiences. Conversely, low win rates might indicate your bids are too conservative. Use first-party data and audience insights to inform your bidding strategy, ensuring you're targeting the right users at the right price.