Base64 Decoder

What is Base64?

Base64 is an encoding that maps any sequence of bytes onto 64 printable ASCII characters — the letters A–Z and a–z, the digits 0–9, and the symbols + and /, plus = as padding. It was standardised in the 1980s to let binary data travel safely through systems that were designed only to handle text. Every three bytes of input become four Base64 characters, which is why Base64-encoded data is always about 33% larger than the binary it represents.

Why decode Base64?

You see Base64 in three places more than anywhere else:

• Email attachments and certificates. PEM-format TLS certificates, SSH keys and the multipart sections of an email are all wrapped in Base64. When something looks like a wall of gibberish letters with the occasional = at the end, decoding it usually reveals the real payload — text, a binary file header, or another encoded layer.
• API payloads. Many APIs return binary blobs (uploaded files, generated PDFs, signed responses) wrapped in Base64 inside a JSON string. The JSON itself is human-readable, but the interesting bit is one decode step away.
• JWTs and HTTP headers. JSON Web Tokens consist of three Base64-encoded segments separated by dots — header, payload, signature. Pasting just the middle segment into this decoder is the fastest way to inspect a token’s claims. HTTP Basic auth headers also pass username:password as Base64; decoding a captured header reveals what the client sent.

In every case the work is the same: paste, click, read.

How to decode Base64 on ToolJutsu

1. Paste your Base64 string into the input box. Whitespace and line breaks are fine — the decoder strips them before doing anything.
2. Click Load sample if you want to see what a successful decode looks like.
3. Read the result in the Decoded text box. As soon as the input is valid, the output updates live — there is no Convert button to click.
4. Click the Copy button to put the decoded text on your clipboard.
5. If the input is not valid Base64, you’ll see a friendly error telling you exactly what went wrong (most often a missing = padding character or a stray non-Base64 symbol).

Common decoding scenarios

When you need file content, not text, the full Base64 Encoder & Decoder tool offers a “decode to file” mode that builds a downloadable blob from the bytes. Use that for anything that decodes to a PNG, a PDF or any other binary payload — this landing is optimised for the single most-asked task, which is “I have a Base64 string and I want to see what it says.”

When you decode a JWT, paste only the middle segment (between the two dots). The first segment is the header (also Base64-encoded JSON), the third is the cryptographic signature (binary, not text). The sibling JWT Decoder splits all three for you and pretty-prints the JSON.

When the input is URL-safe Base64 (which substitutes - for + and _ for /, and may drop padding), this decoder rejects it. Run the input through Find & Replace first to swap the characters back, then come here.

Privacy

The decoder reads your input from the textarea, runs the browser’s built-in atob to turn each four-character group back into three bytes, then hands the bytes to a TextDecoder set to UTF-8. All three steps run synchronously in JavaScript on your device. The page makes no network requests after the initial JavaScript loads, so neither ToolJutsu nor anyone else sees your input — including the contents of any tokens, certificates or API responses you paste in.

Compatibility notes

Modern browsers ship atob and TextDecoder natively, so the decoder works in Chrome 38+, Firefox 19+, Safari 10+, Edge, and every mobile browser of the last decade. No polyfills, no fallbacks. If you need to decode programmatically rather than through a web page, the same one-line atob + TextDecoder('utf-8') recipe works in every JavaScript environment.