As long as it's reciprocal. No fair if you just want to snoop without handing over your phone for inspection as well.
How to see someone else's texts?
I assume that you're asking this because you are suspicious about actions of your partner. Speaking from personal experience, intuitions are usually correct and you may want to consider moving on from this person, if things were going great between you two you would not be asking this question or feeling the need to read his or her text messages. Truth is you can't see anyone else text unless you take the phone and read them yourself, those spy text apps are scams for money.
You have to ask that person and see if they're willing to show you.
Look at their phone.
What youre asking here may be requesting illegal information as this would legally constitute hacking without the persons permission therefore is a crime so best to forget this idea
Ask the person about their texts. If they don't want to show you, then a boundary has been identified. You need to observe boundaries. To do anything else is disrespectful. But there are trust issues that will become clear and that is the thing that is at the core of all this. Deal with the trust issues instead of the texts. It may be time for you to move on. You cannot, and should not, control other people's behavior