§ 109 GewO distinguishes between a simple and a qualified employment reference. Both must be issued in writing; the difference lies in the content.
Simple employment reference
Contains information on the type and duration of the employment — i.e. who worked when and in which position. No assessment of performance or conduct.
The employee can request it at any time. The employer may issue it if no assessment is requested or customary.
Qualified employment reference
Additionally contains a performance and conduct assessment in the established reference language. It is the standard case in most industries and for longer employment.
If a qualified reference is requested, the employer must in principle issue it — unless justified reasons speak against it (rare).
Practice
In HR practice, the qualified reference is the standard. The simple reference mainly appears for very short employments or on explicit request.
Zeugnis generates qualified references by default with all required sections according to § 109 GewO.