• gin

package main:

import (
  "fmt";
  "net/http";
  "github.com/gin-gonic/gin";
);

func main() {
  r := gin.Default();
  r.GET("/", func(c *gin.Context) {
    fmt.Println("------ welcome to gin ------");
    // --- string ---
    // c.String(http.StatusOK, "Hello World");
    // --- json ---
    c.JSON(http.StatusOK, gin.H{ "message": "Hello World" });
  });
  r.Run(":3001");
}

• fiber

package main;

import (
  "fmt";
  "github.com/gofiber/fiber/v2";
);

func main() {
  app := fiber.New();
  app.Get("/", func(c *fiber.Ctx) error {
    fmt.Println("------ welcome to fiber ------");
    // --- string ---
    // return c.SendString("Hello World");
    // --- json ---
    return c.JSON(fiber.Map{
      "message": "Hello World",
    });
  });
}