OpenRTB 2.6 Required and Recommended Fields at a Glance

Purpose

This document provides a compact table-based reference to the core objects and fields that should be checked first when reading OpenRTB 2.6 or reviewing an implementation.

Key Takeaways

• Required means the field is fundamentally required by the OpenRTB 2.6 specification.
• Conditionally Required means the field becomes required when a given format or transaction context applies.
• Recommended fields are not always strictly mandatory in the spec, but they strongly influence transaction quality and interpretability in practice.
• The important distinction is between spec status and practical importance.

How to Read This Page

Label	Meaning
Required	Fundamentally required by the OpenRTB 2.6 spec
Conditionally Required	Required when a specific object or format is in use
Recommended	Strongly recommended or generally expected in practice
Optional	Optional in the spec, but still important in certain transaction contexts

1. Top-Level BidRequest Objects

Object / Field	Spec Status	Practical Importance	Description
id	Required	Very high	Unique identifier for the overall bid request.
imp[]	Required	Very high	Array of actual ad opportunities. At least one imp is required.
site	Recommended	Very high	Describes the web or mobile web context.
app	Recommended	Very high	Describes the app or CTV app context.
device	Recommended	High	Carries device, identity, location, and tracking restriction signals.
user	Recommended	High	Carries user identity and audience context.
regs	Optional	High	Important for privacy, COPPA, and regulatory interpretation.
source	Optional	High	Adds transaction context such as supply path, transaction ID, and payment chain.

2. Imp and Format Objects

Object / Field	Spec Status	Practical Importance	Description
imp.id	Required	Very high	Identifies each ad opportunity within the request.
banner	Conditionally Required	High	Required when the opportunity is a banner ad.
video	Conditionally Required	Very high	Required when the opportunity is a video ad.
audio	Conditionally Required	High	Required when the opportunity is an audio ad.
native	Conditionally Required	High	Required when the opportunity is a native ad.
pmp	Optional	High	Important when PMP or direct-deal context is present.
metric[]	Optional	Medium	Carries exchange-provided performance or quality metrics.
banner.format[]	Recommended	High	Defines the allowed banner size candidates.
video.mimes	Required	Very high	Lists the supported video MIME types.
video.protocols	Recommended	Very high	Declares supported VAST/protocol combinations.
audio.mimes	Required	High	Lists the supported audio MIME types.
native.request	Required	Very high	Carries the Native Ad Specification request payload.

3. Frequently Reviewed Detailed Fields

Object / Field	Spec Status	Practical Importance	Description
source.fd	Recommended	Medium	Indicates whether the exchange or an upstream source made the final sale decision.
source.tid	Recommended	High	Common transaction ID shared across participants for reconciliation.
source.pchain	Recommended	Medium	Carries payment chain information.
deal.id	Required	Very high	Unique identifier for a PMP or direct deal.
site.id	Recommended	High	Exchange-defined site identifier.
app.id	Recommended	High	Exchange-defined app identifier.
device.ua	Recommended	High	Browser or runtime user-agent signal.
device.ip	Recommended	High	Commonly used for geo and network context.
device.dnt	Recommended	High	Do Not Track signal.
device.lmt	Recommended	Very high	Limit Ad Tracking signal with strong practical impact.
user.id	Recommended	High	Exchange-defined user identifier.
user.buyeruid	Recommended	High	Buyer-mapped user identifier.
user.data[]	Optional	High	Array of Data objects carrying user or audience data signals.
data.segment[]	Optional	High	Segment array that can represent audience, interest, or taxonomy nodes.
segment.id	Optional	High	Segment identifier used for matching, filtering, and reporting.
segment.name	Optional	Medium	Human-readable display value. Logic should usually rely on id.
metric.type	Required	Medium	The metric name, typically pre-agreed with bidders.
metric.value	Required	Medium	The metric value. Probabilistic values should be in the 0.0 to 1.0 range.
metric.vendor	Recommended	Medium	Describes the metric source.

Implementation Notes

• site and app are generally not used together. The channel context determines which one is primary.
• In real SSP, DSP, and measurement integrations, many recommended fields are treated as practically essential.
• Signals such as source, regs, schain, and ID provenance extend the trust layer beyond a narrow required-field checklist.
• Internal labels such as lvl1, lvl2, and lvl3 should not be exposed as external standard fields. They are safer to interpret through user.data[].segment[] and a taxonomy ID scheme.
• This page should be read as a quick reference. For design or implementation review, it works best alongside the more detailed object-level documents.

Next Documents

• How to Read site, app, and imp
• How to read OpenRTB top-level control fields
• Audience data and taxonomy signaling
• What OpenRTB 3.0 aimed for and what returned in 2.6

Related Documents

• What Is OpenRTB
• Understanding sellers.json and schain

Official References

• OpenRTB 2.6 PDF
• IAB Tech Lab OpenRTB Standard
• The OpenRTB updates you should adopt in 2025