Das Futur II
Werden (to become) is conjugated in the present tense and it makes a sentence frame with the perfect infinitive of the main verb:
werden + perfect infinitive
conjugated in the present tense
There are no irregular verbs in the future tense though the forms of werden are irregular.
lesen (to read)
ich werde gelesen haben
du wirst gelesen haben
er wird gelesen haben
wir werden gelesen haben
ihr werdet gelesen haben
sie werden gelesen haben
The sentence frame means that the infinitive form of the main verb comes at the end of the sentence, it does not inevitably follow right after the form of werden:
Er wird geschrieben haben. (He must have written.)
Er wird einen Brief geschrieben haben (He must have written a letter.)
Er wird gestern einen Brief geschrieben haben. (Yesterday he must have written a letter.)
Usage of Futur II: it does not express future actions. The name “Futur II” is quite misleading as it mostly expresses possibility for the past; it expresses the same meaning as the English “must + perfect infinitive” structure, see the examples above.
More rarely the Futur II can express a future action that will probably or surely be finished by a certain point of the future. In this case the verb in the sentence is mostly beenden (to finish) and the sentence contains a time adverb that refers to the future (e.g. morgen ‘tomorrow’):
Morgen wird er die Arbeit beendet haben = Tomorrow he will surely have finished the work.