You can buy strawberry syrup in some grocery stores, but it’s usually thick – meant for pancakes rather than drinks – and may have a bunch of other additives you don’t need.
Like all fruit syrups, strawberry is made with strawberries, sugar, and water in a 4:2:1 ratio. Remove the strawberry caps and quarter the berries. Bring the ingredients together in a pot over medium-low heat and simmer for about 20 minutes, stirring occasionally and skimming off foam, until the fruit softens and breaks down. Strain out the fruit and return the liquid to a simmer, reducing it until it’s at a syrupy consistency. Let it cool, pour it in a jar, and store refrigerated for up to two weeks.