In a small saucepan over medium heat, combine the water and granulated sugar. Stir until the sugar dissolves completely, creating a simple syrup base.
Sift the unsweetened cocoa powder and gradually whisk it in, ensuring there are no lumps. Continue stirring until the mixture becomes smooth and well combined.
Pour in the strong brewed coffee and vanilla. Keep stirring to maintain a smooth consistency. Add a pinch of salt.
Allow the mixture to simmer for about 5-7 minutes, allowing the flavors to meld and the syrup to thicken slightly. Stir occasionally to prevent sticking.
Once the mocha syrup reaches your desired consistency, remove it from heat and let it cool. Transfer the cooled mocha syrup into a clean, airtight container. Store it in the refrigerator for up to a month.