3 Easy Ways to Pretty Print JSON in Golang

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There are three ways to pretty print json in Go.

  1. Using “json.MarshalIndent()” function
  2. Using “json.Indent()” function
  3. Using “Encoder.SetIndent()” function

Method 1: Using json.MarshalIndent()

The json.MarshalIndent() function accepts in the interface we want to marshal as well as the prefix string and the indent string.

Example

package main

import (
  "encoding/json"
  "fmt"
)

func main() {
  sample_data := map[string]interface{}{
    "car": "Lamborghini",
    "company": "Volkswagen",
    "specs": map[string]string{
               "Fuel Type": "Petrol",
               "Transmission Type": "Automatic",
          },
  }
  formatted_data, err := json.MarshalIndent(sample_data, "", " ")
  
  if err != nil {
    fmt.Println(err)
    return
  }
  fmt.Println(string(formatted_data))
}

Output

{
  "car": "Lamborghini",
  "company": "Volkswagen",
  "specs": {
     "Fuel Type": "Petrol",
     "Transmission Type": "Automatic"
  }
}

The json.MarshalIndent() function accepts the JSON data(sample_data) as a byte slice and an optional prefix(“”) and indentation string(” “) and returns the indented JSON data as a byte slice.

Method 2: Using json.Indent()

The json.Indent() function is from a package json/encoding that beautifies the JSON string without indentation to JSON with indentation.

Example

package main

import (
  "bytes"
  "encoding/json"
  "log"
  "os"
)

func main() {
  type Company struct {
    Name string
    Number int
    Unit string
  }
  company := []Company{
      {"Lamborghini", 1, "million"},
      {"Buggati", 3, "million"},
  }

  bt, err := json.Marshal(company)
  if err != nil {
    log.Fatal(err)
  }

  var out bytes.Buffer
  json.Indent(&out, bt, "", " ")
  out.WriteTo(os.Stdout)
  println("\n")
}

Output

[
 {
   "Name": "Lamborghini",
   "Number": 1,
   "Unit": "million"
 },
 {
   "Name": "Buggati",
   "Number": 3,
   "Unit": "million"
 }
]

Method 3: Using Encoder.SetIndent()

The SetIndent() function instructs the encoder to format each subsequent encoded value as if indented by the package-level function. Using the json.Encode() function, you can set indentation through Encoder.SetIndent() method is similar to marshaling by defining a prefix and indent.

Example

package main

import (
  "bytes"
  "encoding/json"
  "fmt"
  "log"
)

func PrettyString(str string) (string, error) {
  var prettyJSON bytes.Buffer
  if err := json.Indent(&prettyJSON, []byte(str), "", " "); err != nil {
    return "", err
  }
  return prettyJSON.String(), nil
}

func main() {
  animalJSON := `{"type": "Cat", "name": "Fluffy", "age": 5}`
  res, err := PrettyString(animalJSON)
  
  if err != nil {
    log.Fatal(err)
  }
  fmt.Println(res)
}

Output

{
  "type": "Cat",
  "name": "Fluffy",
  "age": 5
}

That’s it.