Learn Hardcore German: Jede Rezension wird von der Bibliothek bewertet und im System gespeichert. - Each review is rated by the library and saved in the system.

This sentence focuses on the action (the review being assessed and stored) rather than the doer. In German, the present‐tense passive is formed with:

werden (conjugated)
- past participle of the main verb
- (optional) agent introduced by von
  - dative

Here you have wird (present of werden) + bewertet (Partizip II of bewerten) and the second participle gespeichert.

Why is Jede Rezension in the nominative case and placed at the beginning?

Even in the passive, the grammatical subject (the thing being acted on) is in the nominative. Jede Rezension (“each review”) is the subject of wird bewertet, so it takes nominative and appears first because German generally puts the finite verb in second position.

Why do we use von der Bibliothek and why is Bibliothek in the dative?

In a German passive, the agent (the one doing the action) is introduced with von + dative case. Since die Bibliothek is feminine, its dative article is der, giving von der Bibliothek.

Why is there only one wird before bewertet and not another before gespeichert?

German allows you to share one conjugated auxiliary (wird) with multiple past participles in a row. So wird bewertet und gespeichert is perfectly correct—the single wird applies to both verbs.

Why is im System used and what case is that?

im is the contraction of in + dem. Here in expresses location (“where something is stored”), which takes the dative. Hence im System means “in the system” with System in the dative case.

Could you show me the active‐voice version of this sentence?

Sure. Turning agent into the subject and the object back into the direct object, you get:
Die Bibliothek bewertet jede Rezension und speichert sie im System.

Why is Bibliothek capitalized?

All German nouns are always capitalized. Since Bibliothek is a noun (“library”), it must begin with a capital letter.