Der Widerruf ist schriftlich.

Because Widerruf is the subject of the sentence, so it is in the nominative case.

• der Widerruf = nominative
• den Widerruf = accusative

In Der Widerruf ist schriftlich, the thing doing the being is the revocation, so German uses nominative.

A useful pattern:

• Der Vertrag ist gültig.
• Der Antrag ist vollständig.
• Der Widerruf ist schriftlich.

In all of these, the noun before ist is nominative.

Yes. Widerruf is a masculine noun in German, so its dictionary form is der Widerruf.

That is something you usually just have to learn together with the noun:

• der Widerruf
• plural: die Widerrufe

For English speakers, grammatical gender can feel arbitrary, so it is best to memorize new nouns with their article from the start.

Because here schriftlich comes after the verb ist and functions as a predicate adjective.

In German, adjectives used this way do not take adjective endings.

Compare:

• der schriftliche Widerruf = the written revocation
  
  • here the adjective is before the noun, so it takes an ending
• Der Widerruf ist schriftlich.
  
  • here the adjective is after ist, so it stays in its basic form

This is very common:

• Der Vertrag ist gültig.
• Die Antwort ist richtig.
• Das Formular ist vollständig.

Traditionally, it is best understood here as an adjective used predicatively.

That means it describes the subject:

• Der Widerruf — what is it like?
• It is schriftlich

English often uses in writing here, which looks like a prepositional phrase rather than an adjective. German often uses an adjective where English uses a different structure.

So grammatically in German, schriftlich behaves like an adjective after sein.

In this sentence, it usually means in writing.

That is an important nuance. It does not usually mean that the revocation itself is physically a written object in some descriptive sense. Instead, it means that the revocation must exist in written form or be made by writing.

So in practical/legal language:

• mündlich = oral / spoken
• schriftlich = in writing / written

That is why this kind of sentence often appears in formal or legal contexts.

Because this is a normal main clause, and German main clauses usually put the finite verb in second position.

So the pattern is:

• Der Widerruf = first element
• ist = second position
• schriftlich = rest of the clause

This is standard German word order.

You could also change the first element for emphasis:

• Schriftlich ist der Widerruf.

But that sounds marked or stylistically unusual in most contexts. The normal neutral order is:

• Der Widerruf ist schriftlich.

Because all nouns are capitalized in German.

So:

• der Widerruf
• die Frist
• das Formular

But adjectives and verbs are normally not capitalized unless they begin the sentence:

• schriftlich
• ist

This is one of the most noticeable spelling differences between German and English.

Yes, it is grammatical, but it sounds formal and somewhat legal or administrative.

In everyday speech, people might use a fuller version such as:

• Der Widerruf muss schriftlich erfolgen.
• Ein Widerruf muss schriftlich eingereicht werden.

But short forms like Der Widerruf ist schriftlich can appear in rules, contracts, instructions, and legal texts, where concise wording is common.

So if it sounds a bit stiff, that is because the register is formal.

No, that would not be the normal way to say it.

German idiomatically uses schriftlich for in writing in this kind of context.

Natural options include:

• Der Widerruf ist schriftlich.
• Der Widerruf muss schriftlich erfolgen.
• Der Widerruf muss in schriftlicher Form erfolgen.

But in Schrift is not the usual expression here.

Ist is the 3rd person singular present tense form of sein = to be.

The subject is der Widerruf, which is singular, so German uses:

• ich bin
• du bist
• er/sie/es ist

In this sentence, ist links the subject to the description schriftlich. This is called a linking verb use of sein.

So the structure is:

• subject: Der Widerruf
• linking verb: ist
• predicate adjective: schriftlich

It is pronounced approximately like:

VEE-der-roof

A few useful notes:

• W in German sounds like English v
• the ie in Wi- is a long ee sound
• the r may sound different depending on accent
• the final -ruf sounds like roof, but with a German u

Stress is on the last syllable:

• widerRUF

So: wider-RUF