Base64 decoder

Paste your payload into the text area and this free base64 decoder converts it back to plain text. You get the raw string immediately without signing up.

How the base64 decoder processes input

Base64 takes binary data and maps it to a 64-character ASCII alphabet. Every three bytes of input become four encoded characters. When you run a base64 to text conversion, the tool reverses this math. It reads four characters, looks up their six-bit values, and stitches the bits back into eight-bit bytes. This process guarantees that binary data survives transit through systems that only handle plain text.

The alphabet uses A-Z, a-z, 0-9, plus, and slash. If your input length isn't a multiple of four, the decoder expects padding. You will see one or two equals signs at the end. Those equals signs tell the parser how many missing bits to ignore when reconstructing the final byte.

Practical situations for an online base64 decoder

Developers hit this tool when debugging HTTP headers or inspecting JSON Web Tokens. A JWT payload sits in the middle of the token, separated by dots. You copy that middle section, paste it here, and read the claims. It saves you from writing a quick script just to read a token.

You also need it for data URIs. Images embedded directly in CSS start with a prefix containing the text data:image/png;base64. Stripping that prefix leaves the raw encoded image data. Pasting the remainder into a free base64 decoder reveals the underlying binary structure.

• Debugging Basic Authentication headers in network tabs.
• Extracting configuration payloads from obfuscated scripts.
• Reading SAML assertions during single sign-on troubleshooting.

Edge cases and decoding limits

This tool expects standard RFC 4648 encoding. It will fail if you paste URL-safe Base64 without converting the hyphens and underscores back to plus and slash first. Whitespace usually gets ignored, but stray newline characters in the middle of a block can sometimes break strict parsers. Always strip surrounding whitespace if the decode fails unexpectedly.

You must also handle character encoding on your end. The decoder outputs raw bytes. If those bytes represent UTF-8 text, your browser will render them correctly. If they represent UTF-16 or a legacy code page, you will see mojibake. The tool doesn't guess your text encoding, so you need to know what you are decoding.

How to use the base64 decoder

1. Copy the encoded string from your source code or network inspector.
2. Paste the text directly into the main input textarea.
3. Remove any data URI prefixes before decoding.
4. Click the decode button to process the payload.
5. Read the resulting plain text in the output area below.

Base64 character set reference

The standard encoding relies on a specific 64-character alphabet plus a padding character.

Frequently asked questions

how to decode base64 with padding errors?

The decoder requires the input length to be a multiple of four. If your string is short by one or two characters, add the missing equals signs to the end. Missing padding is the most common reason a decode operation throws an invalid length error.

does the free base64 decoder work on mobile?

Yes. The interface is fully responsive and runs entirely in your browser. You can paste long encoded strings from your mobile clipboard and get the decoded text without needing a desktop environment.

why does the output show weird symbols instead of text?

You are likely looking at raw binary data or a different character encoding. The tool outputs the exact bytes it reconstructs. If the original data was an image or a UTF-16 string, your terminal or browser will display garbage characters instead of readable English text.

can I decode URL-safe base64 strings here?

Not directly. URL-safe encoding replaces the plus and slash characters with hyphens and underscores. You need to swap those characters back to the standard alphabet before pasting the string into this online base64 decoder, or it will throw an invalid character error.