How to set http.ResponseWriter Content-Type header globally for all API endpoints?
You can define middleware for mux router, here is an example: func main() { port := “:3000” var router = mux.NewRouter() router.Use(commonMiddleware) router.HandleFunc(“/m/{msg}”, handleMessage).Methods(“GET”) router.HandleFunc(“/n/{num}”, handleNumber).Methods(“GET”) // rest of code goes here } func commonMiddleware(next http.Handler) http.Handler { return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { w.Header().Add(“Content-Type”, “application/json”) next.ServeHTTP(w, r) }) } Read more in the documentation