willing
His letter proves his willingness to help.
He expressed a willingness to be of service.
The willingness of people to get involved has impressed the organizers of the event.
These problems can be solved. It's just a question of willingness.

SMART Vocabulary: related words and phrases

Ready and willing
agreeable
amenable
at someone's beck and callidiom
at your commandidiom
be chafing at the bitidiom
beck
command
concert pitch
disposed
eager
eagerly
fain
finger
keen
pleased
poised
prepared
raring
readily
ripe