Let's say someone was asked "are you going to shul tomorrow?" and the other person answers "yes." Does that count as a Neder?
BTW Rav Mutzafi says that Nedarim are only on Mitzvot, Torah etc.
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It's certainly not a neder, as per Nedarim 2b:
דתנא נדרים דמיתסר חפצא עליה... לאפוקי שבועה דקאסר נפשיה מן חפצא
It taught nedarim where one forbids an object on himself, and excluded shevuot where one forbids one's self from the object.
It might be a Shevua, though, as per Shevuos 3:1:
שְׁבוּעוֹת שְׁתַּיִם שֶׁהֵן אַרְבַּע, שְׁבוּעָה שֶׁאֹכַל וְשֶׁלֹּא אֹכַל, שֶׁאָכַלְתִּי וְשֶׁלֹּא אָכַלְתִּי.
There are two types of Shevuos, which are four: A Shevuah that I will eat or will not eat, that I ate or that I did not eat.
Your case would be comparable to "I will eat." The problem is that all throughout Shevuos we find that a Shevuah can only be made in one of two ways: actually swearing to that effect (every case is introduced as "Shevuah that I...") or someone adjuring you to swear, to which you answer "Amen" or some other form of acceptance (Rambam, Shevuos 2:1ff). Because of this, it would seem that it is not considered a Shevuah, either.