bereit sein
to be ready
To be prepared and willing to do something or for something to happen.
Ich bin bereit, wir können losfahren.
I'm ready; we can set off.

ready
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to be ready
To be prepared and willing to do something or for something to happen.
Ich bin bereit, wir können losfahren.
I'm ready; we can set off.

The adjective 'bereit' (ready) belongs to the word family of 'bereiten' (to prepare) and 'Vorbereitung' (preparation). All of these words have to do with preparing for an action or event.
Nach langer Vorbereitung war die Mannschaft bereit für das Finale.
After a long period of preparation, the team was ready for the final.
'Bereit' (ready) is almost always used predicatively with the verb 'sein' (to be), meaning after the noun. Using it directly before a noun, for example 'der bereite Läufer', is very rare and sounds unnatural.
Die Sportler sind bereit für den Wettkampf.
The athletes are ready for the competition.
To express what someone is willing to do, you use a construction with 'zu'. Either a noun in the dative follows ('bereit zu einem Kompromiss' — willing to make a compromise), or an infinitive clause follows ('bereit, einen Kompromiss zu machen' — willing to make a compromise).
Der Politiker ist zu einem Gespräch mit der Opposition bereit.
The politician is willing to have a conversation with the opposition.
In the meaning 'to wait for deployment/action,' the reflexive verb 'sich bereithalten' (to stand by) is used. The reflexive pronoun (sich, mich, dich, etc.) must always be included and match the person.
Die Feuerwehr hält sich für mögliche Waldbrände bereit.
The fire department is standing by for possible forest fires.
clear
'klar' and 'bereit' can both express that someone or something is prepared for an action. 'bereit' is the normal everyday word and also means that someone wants to do something or accepts it. 'klar' in this sense is much more specific and sounds more technical, nautical, or used in fixed situations like 'klar zum Start' (ready for takeoff). Learners may confuse them because both have to do with preparation. In everyday language, 'bereit' is usually more natural.

Vor dem Termin ist er bereit, die neuen Unterlagen zu unterschreiben.
Before the appointment, he is ready to sign the new documents.
Das Boot ist klar zum Ablegen.
The boat is ready to cast off.