I’d be honest and specific, but keep the reference relevant to the level and role the other club is considering.
Talk about strengths you have genuinely seen: technical qualities, game understanding, physical profile, consistency, attitude and how they respond to coaching.
If there are development areas, describe them constructively rather than hiding them.
I would avoid making predictions you cannot support, such as saying a player will definitely succeed at a certain level.
The other coach is usually trying to understand fit, not receive a sales pitch.
I’d also tell the player that you have been asked and, where appropriate, explain the type of information you intend to give.
A trustworthy reference helps the player more than an exaggerated one.
If the receiving club discovers quickly that your description was unrealistic, that can damage both the player’s experience and your credibility.
Good pathway support means advocating honestly, not pretending every player has no weaknesses.