When you eat at a restaurant- check the bottom of the bill for taxes and service fees. It is standard to tip 10%. Some restaurants add a service or gratuity to the final bill and some do not  but this does not equate to a tip for the service staff. 

Be aware that your waitperson receives none of the service charge. It is simply additional profit for the restaurants, which keep the entire amount. Many restaurants also keep any cash tips left on the table.

Even at many fine dining establishments, most servers make SGD $6 (about USD $4.80) per hour in Singapore. If you wish to leave a tip specifically for them, it is best to hand cash directly to them while thanking them for their service. 

At hotels and spas, it is not customary to tip other than bellhops.  It is also not customary to tip taxi drivers or tour guides in Singapore.