Base64 decoder

Decode a Base64 string back to its original text or binary form.

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Base64 Decoder: Decoding Base64 Strings

A Base64 decoder takes a Base64-encoded string and converts it back to its original form — whether that is plain text, binary data, or an image. Decoding is the reverse of encoding and is used to retrieve the original data from its Base64 representation.

How Base64 Decoding Works

The decoder reads the Base64 string, maps each character back to its 6-bit value, and reassembles the original bytes. Padding characters (=) are used to indicate the end of the data and are removed during decoding. The result is the exact original input, assuming the Base64 string was valid.

Common Uses of Base64 Decoding

Reading email attachments: MIME-encoded attachments are Base64 strings that need to be decoded to access the original file.
Extracting data from data URLs: Embedded images and resources in HTML/CSS are Base64-encoded and must be decoded to be used.
API responses: Some APIs return binary data as Base64 strings.
Debugging: Developers decode Base64 strings to inspect the original data.

Base64 Decoding Errors

If the input is not valid Base64, decoding will fail or produce garbled output. Common causes include:

Invalid characters (e.g., characters outside the Base64 alphabet).
Incorrect padding.
Truncated input.
URL-safe Base64 being decoded with a standard decoder (or vice versa).

When decoding, always ensure you are using the correct variant.

Decoding vs. Decrypting

Decoding is not decryption. Base64 is not encryption, so anyone can decode a Base64 string. If the original data was encrypted before being Base64-encoded, you need the decryption key to recover the plaintext. Base64 alone provides no security.

Practical Example

Decoding aGVsbG8= returns hello. Decoding SGVsbG8sIFdvcmxkIQ== returns Hello, World!. The process is fast and lossless.

Conclusion

Base64 decoding is a simple but essential operation for working with encoded data. It reverses the encoding process and restores the original input. Use it whenever you encounter Base64 strings in emails, APIs, or web resources.