Mercury in Libra, both sides of the question
Mercury in Libra means you think by weighing, and you see the other side of an argument before you've finished making your own. You speak diplomatically, choose words for how they'll land, and do your best thinking in conversation with someone else.
Mercury is the planet of the mind and the voice: how you decide, how you argue, what you notice first. Libra is cardinal air, ruled by Venus, so the mind here starts things through conversation and cares about how a sentence sounds as much as what it says.
Drafting the reply three times
You rewrite messages before you send them. A plain "can't make it" becomes "so sorry, I don't think I can make it this time, but let's find another day!" You soften requests with "just" and "no worries if not". In a discussion you ask "what do you think?" before saying what you think, partly from good manners and partly to find out where the balance point is.
You're the mediator in the group chat. When two friends fall out, both of them call you, and you can explain each one's position to the other better than they could themselves. You learn through talking: a study partner, a debate, a teacher who'd discuss the material instead of reciting it. Ideas you've only read stay flat until you've argued about them with someone.
What you notice first is imbalance. The person who hasn't spoken all evening, the deal that's unfair to one side, the clumsy sentence in an otherwise good letter.
Undecided
The honest tension is the decision you can't make. Choosing a restaurant takes twenty minutes because every option has a fair case. In a larger question, the job, the move, the hard conversation, you keep collecting perspectives long after you have enough of them, and the decision gets made by the deadline instead of by you.
Your own opinion also goes missing. To keep the peace you agree in the moment, then think it through afterwards and realize you didn't agree at all. People close to you say they can't always tell where you stand, and some of them stop asking.
Alongside your Sun
Mercury stays within a sign of the Sun, so your Sun is in Virgo, Libra or Scorpio. With a Virgo Sun, a critical, exact mind speaks through a gracious voice, and your criticism arrives so politely that people miss it. With a Libra Sun, fairness runs through everything you think and say. With a Scorpio Sun, the pleasant manner covers a deep, private read of everyone in the room.
The opposite placement, Mercury in Aries, says the first thing it thinks and moves on. You'd find it rude; it would find you slow, and each has something to teach the other. The Mercury sign guide shows how to find yours.
Questions
How does Mercury in Libra communicate?
Diplomatically and with care for how things sound. You listen, reflect the other side back, and phrase hard things gently.
Is Mercury in Libra indecisive?
About things where every option has a fair case, yes. You see the merits of each choice so clearly that picking one feels like a loss, so a deadline or a trusted second opinion helps.
Is Mercury in Libra smart?
It's a balanced, comparative intelligence: excellent at weighing arguments, seeing every side and finding the fair solution. It's slower when it has to choose alone.