Base64 Decoder
Decode any Base64 string back to plain text instantly. Free, no signup.
How to use this tool
- Enter base64 to decode in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your decoded text and the full breakdown beneath it.
Base64 Decode converts a Base64-encoded string back into its original text form.
How it works
This tool decodes a Base64-encoded string back into its original plain text. Base64 decoding is the reverse of encoding: the tool takes a string of Base64 characters and reconstructs the original bytes, then displays them as readable text.
Paste a Base64 string into the input field and click Decode. The tool validates that the input is valid Base64 (correct character set and padding), converts each group of four characters back to three bytes, and displays the decoded result as UTF-8 text.
You will use this when you receive a Base64 payload and need to read it, such as inspecting a JWT token's payload, reading an encoded configuration value from an environment variable, checking what credentials are stored in a Basic Auth header, or previewing the content of a data URI.
Decoding runs entirely in your browser with no server contact. If the input contains characters outside the Base64 alphabet (spaces, punctuation other than + and /, or extra line breaks), the tool will flag the error so you can clean up the input.
Worked example
Read the payload of a JWT token
- Copy the middle segment of your JWT (between the first and second dot)
- Paste it into the decoder input
- Click Decode
- Read the JSON payload showing user ID, roles, and expiry
{"sub":"12345","role":"admin","exp":1893456000}
Common mistakes to avoid
- Pasting the full JWT including the header and signature dots instead of just the payload segment.
- Not removing whitespace or line breaks from the input, which causes an invalid-character error.
- Expecting the decoded output to always be readable text -- binary content will appear as garbled characters.
Key terms
- Base64 alphabet
- The 64 characters used in Base64 encoding: A-Z (26), a-z (26), 0-9 (10), plus (+) and slash (/), plus equals (=) as a padding character.
- JWT
- JSON Web Token -- a compact, URL-safe token whose payload is Base64url-encoded JSON, commonly used for authentication.
Frequently asked questions
- Why does Base64 decoding fail?
- Decoding fails when the input contains characters outside the Base64 alphabet or has incorrect padding. Ensure the string ends with the right number of '=' characters.