How to Decode and Encode Base64 in Go

The Go standard library provides the encoding/base64 package for all Base64 operations. In Go, you work directly with predefined encoding objects like StdEncoding or URLEncoding.

Byte Slices vs Strings

In Go, standard Base64 functions take a byte slice ([]byte) as input, not a string. You will constantly cast between strings and byte slices using []byte("string") and string(bytes).

1. Encode a String to Base64 in Go

Use base64.StdEncoding.EncodeToString() to convert a byte slice into a Base64 string.

package main

import (
	"encoding/base64"
	"fmt"
)

func main() {
	text := "Hello, Go Base64!"
	
	// Convert string to byte slice and encode
	encoded := base64.StdEncoding.EncodeToString([]byte(text))
	
	fmt.Println("Encoded:", encoded)
	// Output: Encoded: SGVsbG8sIEdvIEJhc2U2NCE=
}

2. Decode a Base64 String in Go

Use base64.StdEncoding.DecodeString() to reverse the process. This function returns two values: the decoded byte slice and an error. You must explicitly check the error.

package main

import (
	"encoding/base64"
	"fmt"
	"log"
)

func main() {
	encoded := "SGVsbG8sIEdvIEJhc2U2NCE="
	
	// DecodeString returns []byte and an error
	decodedBytes, err := base64.StdEncoding.DecodeString(encoded)
	if err != nil {
		log.Fatalf("Failed to decode: %v", err)
	}
	
	// Cast the byte slice back to a string
	fmt.Println("Decoded:", string(decodedBytes))
	// Output: Decoded: Hello, Go Base64!
}

3. URL-Safe Base64 in Go

For URL-safe encoding (replacing + with - and / with _), Go provides the URLEncoding object. If you need to omit the padding (=) entirely, use RawURLEncoding.

package main

import (
	"encoding/base64"
	"fmt"
)

func main() {
	data := []byte("subjects?dir=/usr/local")
	
	// Standard URLEncoding (includes padding '=')
	urlSafe := base64.URLEncoding.EncodeToString(data)
	fmt.Println("URL Safe:    ", urlSafe)
	// Output: c3ViamVjdHM_ZGlyPS91c3IvbG9jYWw=
	
	// RawURLEncoding (omits padding '=') - highly recommended for JWTs
	rawUrlSafe := base64.RawURLEncoding.EncodeToString(data)
	fmt.Println("Raw URL Safe:", rawUrlSafe)
	// Output: c3ViamVjdHM_ZGlyPS91c3IvbG9jYWw
}

Debugging Base64 from Go?

If your Go application outputs a Base64 string that isn't decoding as expected, use our interactive toolkit to inspect the raw characters.

Go to the Base64 Converter Tool