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Base64 Decoder

Base64 Decoder turns a standard Base64 string into text in the browser. URL-safe minus and underscore characters need a swap before they decode.

Standard Base64. A URL-safe alphabet needs a character swap first.
SGk=
Hi

Processing: runs in your browser, nothing uploaded

✓ Free to use✓ No sign-up needed✓ Nothing to install

About Base64 Decoder

APIs, JWTs, and config files hide short text inside Base64. Paste the standard alphabet here and read the text back without sending the string to a server.

Standard Base64 versus base64url

This decoder uses the browser’s atob path on the standard alphabet: A–Z, a–z, 0–9, plus, and slash. A base64url string swaps plus for minus and slash for underscore so it can sit in a URL. Those two characters will fail here until you put plus and slash back. Padding with equals signs belongs on standard Base64; if the tail was stripped, add equals until the length is a multiple of four, then try again. This page does not flip the URL-safe alphabet for you.

Text, not a picture

The result is decoded as text. A Base64 image, font, or PDF will look like garbage characters, not a preview. For a picture, use Base64 to Image and paste the payload or the data URI there. If the string starts with data:image and a comma, delete that prefix before decoding text. JWT Decoder is the right page when the value is three dot-separated parts: it splits header and payload instead of treating the whole token as one blob.

Round-trip and secrets

Encode with Base64 Encoder when you need the opposite direction, including non-English text. Hex Decoder is for hex bytes, not this alphabet. Decoding does not mean the content is safe to paste into chat. Tokens and passwords are still secrets after they become readable. Decode them locally, copy what you need, and clear the box. A string that fails with an invalid character error often still has a line break or a data-URI prefix attached.

How to use

  1. 1

    Paste a standard Base64 string, without a data: prefix.

  2. 2

    If the alphabet is URL-safe, swap minus to plus and underscore to slash, and restore equals padding.

  3. 3

    Run the decoder and copy the text. Use Base64 to Image instead when the payload is a picture.

Privacy

Decoding runs in the browser. The string is not sent to FileToolsHub.

Frequently asked questions

Can this base64url decoder accept minus and underscore?

Not directly. Replace minus with plus and underscore with slash, then add equals padding if the length is not a multiple of four.

Why does my image look like random text?

This page decodes to text. Use Base64 to Image when the payload is a picture or a data URI.

Do I include the data: prefix?

No. Delete everything through the comma so only the Base64 payload remains.

Is padding required?

Standard Base64 is defined in groups of four characters. If the tail was stripped, add equals signs before you decode.

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