Stock exchanges really cannot be expected to track numbers of outstanding shares.  One puts in a bid or an ask, indicating that one is willing to purchase or sell the given number at the given price, and an order type, indicating the manner to fulfil (fill-or-kill, limit to a certain price, take whatever outstanding offers are necessary...).  This is more than enough nuance for a professional product like a stock exchange that needs to operate at microsecond cadence.<p>If you want to validate whether an order makes sense or is a &quot;good idea&quot;, the place to do it on the client.