The European Commission has launched important updates to the Once-Only Hub. The Hub is primarily for implementers from the EU Member States, building and maintaining the Once-Only Technical System. It is a single environment providing reliable information, services, and support. This release includes both general updates to the content and structure of the site, and additional resources available for those working to implement the Once-Only Technical System.

OOTS Projectathon collaborative space and playbook

The Once-Only Hub now includes a collaborative space for users to prepare for the 2023 Once-Only Technical System Projectathons (April, June, and October 2023). A Projectathon is an event where different systems connect under one roof and perform a marathon of peer-to-peer interoperability and compliance tests in a structured environment for several days.

The Once-Only Technical System Projectathon collaborative space encourages dialogue and exchange of ideas between Projectathon participants in an open and transparent environment.

Sign-up to the space

The European Commission, with the support of experts in the field, has prepared a Participant Playbook to help Projectathon participants make the most of these innovative events.

Read the playbook

API catalogue and technical design documents

The Implementation of the Technical System is coordinated through the Single Digital Gateway Coordination Group and its sub-groups.

Establishing the Once-Only Technical System is a bottom-up exercise, achieved by interconnecting digital services between the EU Member States. There are teams of implementers working for different national administrations throughout the EU building this system.

To this end, the Once-Only Hub provides useful resources for implementers working on elements of the Once-Only Technical System.

Firstly, the Once-Only Technical System uses “Once-Only” supporting services to exchange of evidences between Data Services and Online Procedure Portals. These are referred to as the Common Services, of which there are three:

• Evidence Broker (EB)
• Data Service Directory (DSD)
• Semantic Repository (SR) (in development)

Use the APIs

Secondly, detailed, non-binding technical design documents explain the technical and operational specifications of the Once-Only Technical System. These technical design documents elaborate on Implementing Regulation (EU) 2022/1463) setting out the technical and operational specifications of the Once-Only system. There are six chapters in total:

1. Introduction - High Level Architecture
2. User Identification, Authentication and Record Matching
3. Common Services
4. Evidence Exchange
5. Data Models
6. OOTS Guidance & UX Recommendations

Read the Technical Design Documents

Events and news

A dedicated events and news section means that anyone wanting to learn more about the Once-Only Technical System can easily sign-up to upcoming events, see the slides of previous events and read the latest news, from API software updates to national success stories. You can also sign up to the monthly newsletter and receive this information directly in your inbox.

Register for events

Detailed information about the ‘Once-Only user journey’

The Once-Only Technical System will make administrative processes easier for EU citizens and businesses. It also plays a part in realising Europe’s strategy to build a data-driven economy. However, implementing a data space on the scale of the Once-Only Technical System is a complex and challenging process.

The Once-Only Hub now offers a clear overview of how the system will operate in seven steps:

1. Authentication
2. Evidence location
3. Evidence request
4. Redirection
5. Preview
6. Evidence response
7. Submission

See the user journey