OCDS Extension

The core Open Contracting Data Standard (OCDS) covers the fields common to public procurement across nearly every jurisdiction: tender details, award outcomes, contract values, and payment records. But public procurement is not uniform. A defence contract in France operates under different rules than a utility services contract in Germany or a construction concession in Poland. OCDS extensions are the mechanism that allows publishers to capture jurisdiction-specific or sector-specific data without forking the standard.

What is an OCDS Extension?

An OCDS extension is a formally defined addition to the base OCDS schema. Each extension:

• Defines new fields, objects, or codelists not present in the core standard.
• Is documented in a JSON schema file that describes what each new field means, what type of data it holds, and how it relates to existing OCDS fields.
• Is registered in the OCDS Extension Registry maintained by the Open Contracting Partnership (OCP), making it discoverable and reusable by other publishers facing the same requirements.
• Is declared in a publisher's OCDS package metadata so that data consumers know which extensions are in use and can validate and interpret the data accordingly.

Extensions are optional: a publisher adopts only the extensions relevant to its legal and policy context. When consuming OCDS data, downstream systems should gracefully handle releases that include extension fields, treating unfamiliar fields as additional context rather than errors.

Common extensions in European procurement contexts include:

• The "bids" extension: captures detailed information about individual bids received, including bid values and whether a bid was disqualified, supporting competition analysis.
• The "lots" extension: enables representation of multi-lot procurements, where a single contracting process covers several distinct lots awarded to different suppliers.
• The "beneficial ownership" extension: links contracting data to beneficial ownership disclosures of awarded suppliers.
• The "sustainability" extension: records environmental and social sustainability criteria and their outcomes.
• Country-specific extensions: several national implementations (including Ukraine's Prozorro and UK public procurement data) have developed and registered extensions for fields required by local law.

Why OCDS extensions matter for bidders

Extensions expand the analytical value of OCDS data. The lots extension, for example, makes it possible to analyse a multi-lot framework at the lot level rather than only at the contract level, giving a much more granular picture of how a buyer distributes work across suppliers. The bids extension reveals bid counts and price ranges, enabling competitive benchmarking against what other bidders actually submitted rather than only against the awarded value.

When using a procurement intelligence platform, extensions determine which additional data fields are available beyond the core tender and award fields. A platform that processes the bids extension can tell you how many suppliers competed for a contract and what the price range of bids was. A platform that ignores extensions shows only the winner.

Example

A Dutch ministry publishes OCDS data using the lots extension for a multi-lot consultancy framework covering six specialist advisory areas. Each lot has its own estimated value, award, and awarded supplier. An analytics platform processing this data using the lots extension can show which advisory firms dominate which specialisms, enabling new entrants to identify the most competitive lots and the ones with fewer incumbents.

Frequently Asked Questions

Can any publisher create a new extension?

Yes. Any publisher can draft and propose a new extension. The OCP reviews proposed extensions for quality and documentation before registering them. Registered extensions are preferred over ad hoc custom fields because they enable reuse: if two countries face the same data requirement, using the same registered extension means their data is immediately comparable.

Do I need to understand extensions to use OCDS data?

Not necessarily for basic use. Core OCDS fields covering tender descriptions, values, deadlines, award outcomes, and supplier names are sufficient for most opportunity discovery and market research tasks. Extensions become important when you need deeper analysis: bid count data, lot-level breakdowns, sustainability scores, or ownership disclosures. Platforms that process extensions surface these richer fields automatically.

Are extensions stable, or do they change frequently?

Extensions are versioned. Publishers declare which version of an extension they are using. The OCP encourages backwards-compatible evolution, but breaking changes in major versions do occur. Data consumers should track extension version declarations in publisher package metadata to ensure they are interpreting extended fields correctly.