Base64 Encode & Decode in Swift

Encode or decode below — it runs locally in your browser — then grab the canonical Swift code. Foundation's Data type provides Base64 support: encode a string to Data with .data(using: .utf8), then call .base64EncodedString(), and decode with Data(base64Encoded:).

Encode and decode a string

Encode a String by converting it to Data first, then call base64EncodedString():

import Foundation

// Encode
let encoded = "Hello, world!".data(using: .utf8)!.base64EncodedString()
print(encoded)  // SGVsbG8sIHdvcmxkIQ==

// Decode
let s = "SGVsbG8sIHdvcmxkIQ=="
let decoded = String(data: Data(base64Encoded: s)!, encoding: .utf8)
print(decoded!)  // Hello, world!

URL-safe Base64

Foundation has no built-in URL-safe encoder. Swap +// for -/_ and strip the = padding:

import Foundation

extension Data {
    func base64URLEncodedString() -> String {
        return base64EncodedString()
            .replacingOccurrences(of: "+", with: "-")
            .replacingOccurrences(of: "/", with: "_")
            .trimmingCharacters(in: CharacterSet(charactersIn: "="))
    }
}

let url = "Hello 🌍".data(using: .utf8)!.base64URLEncodedString()

Encode an image (iOS/macOS)

On iOS, get PNG bytes from a UIImage; for any file, read it with Data(contentsOf:):

import Foundation
#if canImport(UIKit)
import UIKit

let base64 = image.pngData()?.base64EncodedString()
#endif

// Any file by URL
let fileData = try Data(contentsOf: fileURL)
let fileBase64 = fileData.base64EncodedString()

Frequently asked questions

How do I Base64 encode a string in Swift?

Convert the string to UTF-8 Data, then encode: "Hello, world!".data(using: .utf8)!.base64EncodedString() returns "SGVsbG8sIHdvcmxkIQ==".

How do I Base64 decode in Swift?

String(data: Data(base64Encoded: s)!, encoding: .utf8) returns the text; Data(base64Encoded:) gives back the bytes.

How do I do URL-safe Base64?

Encode normally, then .replacingOccurrences(of: "+", with: "-") / ("/", "_") and trim the = padding.

Why does Data(base64Encoded:) return nil?

It's a failable initializer — it returns nil for malformed Base64 (bad length, missing padding, invalid characters). Unwrap safely instead of forcing it.