In a medium saucepan, whisk together the cocoa powder, cane sugar, and salt. Break up any clumps in the cocoa powder to ensure a smooth syrup.
Slowly add the water to the dry ingredients while whisking continuously. Keep whisking until the mixture is fully combined and smooth.
Place the saucepan over medium heat and bring the mixture to a boil. Stir frequently to avoid burning or sticking. Once it reaches a boil, stir constantly for 2-3 minutes to thicken.
Remove the saucepan from heat and stir in the vanilla extract.
Let the syrup cool to room temperature in the saucepan. Once cooled, transfer it to a clean jar or container with a lid.