Good question, as there is no consensus or general rule really when it comes to tipping at a restaurant or in an establishment in Spain, nor is it mandatory. So to decide whether to tip (referred to as la propina) or not in Spain, let’s go by what is customary.  To understand what is customary, some background on the food and beverage landscape in Spain, where servers and staff are normally protected by the minimum wage, so tipping is not so much considered part of their more basic income, rather than a (nice) addition to it. So, it is really up to the client to decide whether to tip or not based on the quality of the service they receive. Also, some restaurants may already include service charge, so best to check out the bill beforehand, just in case. Either way, more often than not, it is a generalized practice to tip, usually between 5-10%, ideally 10%.