Base64 Encode & Decode in Go

Encode or decode below — it runs locally in your browser — then grab the canonical Go code. Go's standard-library encoding/base64 package gives you several encodings behind one API: StdEncoding, URLEncoding, and RawURLEncoding.

Encode and decode a string

Convert the string to a []byte, encode it, and on the way back check the error before using the result:

package main

import (
    "encoding/base64"
    "fmt"
)

func main() {
    // Encode
    encoded := base64.StdEncoding.EncodeToString([]byte("Hello, world!"))
    fmt.Println(encoded) // SGVsbG8sIHdvcmxkIQ==

    // Decode
    decoded, err := base64.StdEncoding.DecodeString(encoded)
    if err != nil {
        panic(err)
    }
    fmt.Println(string(decoded)) // Hello, world!
}

URL-safe Base64

For JWTs, URLs, and filenames, use the URL-safe alphabet (- and _ instead of + and /). RawURLEncoding omits padding, which is what JWTs expect:

package main

import (
    "encoding/base64"
    "fmt"
)

func main() {
    data := []byte("a+b/c=d")

    // URL-safe, padded
    fmt.Println(base64.URLEncoding.EncodeToString(data))

    // URL-safe, no padding (JWT-style)
    encoded := base64.RawURLEncoding.EncodeToString(data)
    fmt.Println(encoded)

    // Decode with the matching decoder
    decoded, _ := base64.RawURLEncoding.DecodeString(encoded)
    fmt.Println(string(decoded))
}

Encode bytes / files

Read the file into a byte slice with os.ReadFile, then encode it like any other []byte:

package main

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

func main() {
    data, err := os.ReadFile("image.png")
    if err != nil {
        panic(err)
    }
    encoded := base64.StdEncoding.EncodeToString(data)

    // As a data URI for HTML/CSS:
    fmt.Println("data:image/png;base64," + encoded)
}

Frequently asked questions

How do I Base64 encode a string in Go?

Convert it to a byte slice and encode: base64.StdEncoding.EncodeToString([]byte("Hello, world!")) returns "SGVsbG8sIHdvcmxkIQ==".

How do I Base64 decode in Go?

base64.StdEncoding.DecodeString(s) returns ([]byte, error); check the error, then use string(decoded) for text.

What is the difference between StdEncoding and URLEncoding?

StdEncoding uses + and /; URLEncoding uses - and _; RawURLEncoding is URL-safe with no padding.

How do I do URL-safe Base64?

Use base64.URLEncoding (padded) or base64.RawURLEncoding (no padding, for JWTs), and decode with the matching decoder.