Key-user extensibility
Key-user extensibility (custom fields, custom logic, custom CDS views)
Also known as: in-app extensibility, custom fields
Extending SAP S/4HANA in Fiori apps without development tools: custom fields, custom logic and custom CDS views, transported in software collections.
Key users create custom fields in the Custom Fields app. Each field belongs to a business context and is available only where its usages are enabled: user interfaces and reports, form templates, email templates and APIs.
Key-user custom fields use the YY1_ prefix (developer extensibility uses ZZ1_). Once published, a field keeps its type and its length cannot be reduced; a different type needs a new field and a data migration.
Values reach follow-on documents only through SAP-delivered business scenarios or custom logic. Extension items move between systems in software collections.
In ERP Preflight
Custom Field Flow Doctor traces a field across business contexts; Extension Impact Guard shows what a change or deletion breaks; Software Collection Dependency Guard checks an exported collection before import.
Problems that involve Key-user extensibility
- MajorField declared by the form interface but not populated
- MajorRequested field does not exist in the business source
- MajorField exists in the business source but not in the form data source
- CriticalCustom field not enabled in target business context
- CriticalCustom field cannot propagate across this hop
- MajorCustom field not enabled for a required usage
- MajorCustom field name violates key-user naming
- MajorIncompatible field type or length across a propagation hop
Related terms
Free tools
- Form XML field checker
Does a field path exist in your form data XML, what is its value, are namespaces the problem?
Background articles
- Custom fields with key user extensibility: why a field does not appear in the app, form or APIHow custom fields created with key user extensibility reach UIs, reports, forms and APIs, and why a field that exists on one document is missing on the follow-on document.
Written for ERP Preflight · reviewed September 27, 2026
All glossary termsERP Preflight is independent and not affiliated with SAP SE. SAP, ABAP, Fiori and S/4HANA are trademarks of SAP SE.