Announcing targets

[DylanW18]

Say I cast {Doom Blade}. Does my opponent decide to counter it (with a normal Counterspell) before I announce whom I Doom Blade, or after I declare whom it targets?

[particle]

no you declare targets after you announce the spell. before your opponent can counterspell he will know what you targetted.

[DylanW18]

Awesome thanks! Just wanted clarification +1

[ibtrickey]

It is so that opponent knows if they want to counter it or if it is an allowed target or whatever it is called so it would normally resolve:)

[Pleeb]

601.2c: The player announces his or her choice of an appropriate player, object, or zone for each target the spell requires. A spell may require some targets only if an alternative or additional cost (such as a buyback or kicker cost), or a particular mode, was chosen for it; otherwise, the spell is cast as though it did not require those targets. If the spell has a variable number of targets, the player announces how many targets he or she will choose before he or she announces those targets. The same target can't be chosen multiple times for any one instance of the word "target" on the spell. However, if the spell uses the word "target" in multiple places, the same object, player, or zone can be chosen once for each instance of the word "target" (as long as it fits the targeting criteria). If any effects say that an object or player must be chosen as a target, the player chooses targets so that he or she obeys the maximum possible number of such effects without violating any rules or effects that say that an object or player can't be chosen as a target. The chosen players, objects, and/or zones each become a target of that spell. (Any abilities that trigger when those players, objects, and/or zones become the target of a spell trigger at this point; they'll wait to be put on the stack until the spell has finished being cast.)
Example: If a spell says "Tap two target creatures," then the same creature can't be chosen twice; the spell requires two different legal targets. A spell that says "Destroy target artifact and target land," however, can target the same artifact land twice because it uses the word "target" in multiple places.

Declaring targets is part of the process for casting a spell. The fact that your opponent now knows what the spell is going to hit is a consequence of this process, not a reason for it.  Once it is cast and on the stack, everyone has a chance to respond to it.