Verifier Universal Interface (VUI) is an interoperability working group that aims at building a complete set of standard APIs for Verifier components in SSI ecosystems

As different technology providers build SSI solutions, it becomes critical to ensure interoperability between these solutions. Available standards for SSI still have important gaps, leading us to an ecosystem of full-stack providers whose approach to interoperability is building proprietary plug-ins for each one of the other available solutions. This approach to interoperability is not scalable.

The underlying problem is that building standards take time. That is the reason that we propose a practical and focused approach to enable scalable interoperability in the SSI community.

We propose to start with a specific SSI component, namely the Verifier component, and lead the definition of the minimum set of standard APIs necessary to implement or interoperate with such module. That is, a role-centric approach to standardization at API level.

To date, 12 organisations are contributing to this initiative. The VUI working group has already drafted a first version of a generic spec that integrates existing standards and interop efforts and fills the gaps to provide a complete set of APIs. This draft version can be found at and has been built using ReSpec.

This draft version for VUI includes today 6 APIs:

  • Presentation Exchange
  • Consent Management
  • Schema resolution
  • Issuer resolution
  • ID resolution
  • Credential status resolution

Next steps
As next steps, the Working Group (WG) needs to take this ground work to a more mature level. That is, to further define the specification by achieving consensus in the broader community, and bridging perspectives from DIF, W3C, EBSI, and Aries.

The WG is organized in Working Packages (WP), one for each interface. Any participant can lead or contribute to WP, which shall integrate at least 2 Implementors and 1 Integrator. Implementors are responsible for defining the API, a set of interoperability tests, and service endpoints for Integrators to execute those tests.

The WG has launched a survey in the broad SSI community and two of the 6 interfaces have been selected as initial WPs:

Presentation Exchange
Issuer Resolution

Ready to contribute?
To subscribe to this WG please refer to

Country: Spain
Further information:
Team: Gataca Spain