How to Lowercase JSON Key Names with JSON Marshal in Go

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To lowercase JSON key names with JSON Marshal in Go, you can “add a json tag to each field in your struct, specifying the desired lowercase key name”.

In Golang, the encoding/json package marshals structs into JSON using the field names as JSON key names. By default, it uses the field names as they appear in the struct. However, you can control the JSON key names using the json tag with the omitempty option.

Example

package main

import (
  "encoding/json"
  "fmt"
)

type Person struct {
  FirstName string `json:"firstName"`
  LastName string `json:"lastName"`
  Age int `json:"age"`
}

func main() {
  psn := Person{
    FirstName: "Krunal",
    LastName: "Lathiya",
    Age: 30,
  }

 // Marshal the Person struct into JSON
  jsonData, err := json.Marshal(psn)
    if err != nil {
      fmt.Println("Error marshaling JSON:", err)
      return
  }

  // Print the JSON data
  fmt.Println(string(jsonData))
}

Output

{"firstName":"Krunal","lastName":"Lathiya","age":30}

In this example, we defined a Person struct with FirstName, LastName, and Age fields.

We added the json tags to each field to specify the desired lowercase JSON key names.

When we marshal the Person struct into JSON using json.Marshal(), the resulting JSON object will have lowercase key names as specified in the json tags.

That’s it.

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