Base64 Decoder & Encoder

What is Base64?

Base64 is a binary-to-text encoding that represents arbitrary bytes using 64 printable ASCII characters (A-Z, a-z, 0-9, '+', '/'), with '=' padding so the output length is always a multiple of 4. It's used wherever binary data needs to travel through text-only channels, such as email attachments, data URLs, and JSON/JWT payloads. Because Base64 can represent any bytes, decoding binary data (an image, a compressed file, encrypted bytes) won't produce valid UTF-8 text, so this tool shows a hex dump of the decoded bytes instead. You can also encode a file directly (up to 5MB) using the browser's FileReader API.

Base64 vs. Base64URL: why do JWTs use the URL-safe flavor?

Base64URL swaps '+' for '-' and '/' for '_', and conventionally drops '=' padding, producing output that's safe to embed directly in a URL, filename, or HTTP header without percent-encoding. JWTs (see what is a JWT and how does it work) are base64url-encoded for exactly this reason. Try the JWT decoder to see it in action.

Is Base64 the same as encryption?

No, Base64 is an encoding, not encryption. It is fully and instantly reversible by anyone, with no secret key involved. See security lingo explained: encode vs. encrypt vs. hash for the distinction. Never rely on Base64 alone to keep data confidential.

Encoding/decoding Base64 and Base64URL in .NET

.NET has had Convert.ToBase64String / Convert.FromBase64String for standard Base64 for a long time. For Base64URL, .NET 9 added a dedicated System.Buffers.Text.Base64Url type so you don't have to hand-roll the character substitution and padding yourself:

using System.Buffers.Text;

byte[] bytes = Encoding.UTF8.GetBytes("hello world");

// Standard Base64
string standard = Convert.ToBase64String(bytes);

// Base64URL (.NET 9+), the flavor JWTs use
string urlSafe = Base64Url.EncodeToString(bytes);
byte[] roundTrip = Base64Url.DecodeFromChars(urlSafe);