Use present tense for statements that describe general behavior that's not associated with a particular time.
Recommended: Send a query to the service. The server sends an acknowledgment.
Not recommended: Send a query to the service. The server will send an acknowledgment.
However, it's fine to use future tense (will) to distinguish an action that will occur in the future.
Recommended: Add the filename to the backup list. The file will be archived the next time the backup process runs.
In the following example, future tense is appropriate because Pub/Sub sends messages asynchronously; messages are not received immediately by subscribers.
Recommended: A message is sent that will notify any Pub/Sub subscribers.
Not recommended: A message is sent that notifies any Pub/Sub subscribers.
Don't use future tense to describe how a product or feature will work after the next release or update. For more information, see Document future features.
Also avoid the hypothetical future would—for example:
Recommended: If you send an unsubscribe message, the server removes you from the mailing list.
Not recommended: You can send an unsubscribe message. The server would then remove you from the mailing list.