Checking a token
Confirm an encoded token is valid Base64 before debugging why a decode step fails downstream.
Use Base64 Validator
Converts base64 to result in this tab, with nothing sent anywhere.
Runs entirely on your deviceThe conversion happens in this browser tab. Nothing you type is uploaded, logged or stored, which is worth knowing for anything you would not paste into a search box.
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Browse all developer and data toolsAbout Base64 Validator
A Base64 validator confirms whether a string is genuinely valid Base64 before you try to decode it. Base64 turns binary - an image, a key, a token - into text made only of letters, digits and a few symbols, padded to a length that is a multiple of four. A string that contains a stray character, the wrong padding, or a length that does not divide evenly is not valid Base64 and will fail to decode, often silently. This tool checks the alphabet, the padding and the length in your browser and tells you whether the string is valid, and how many bytes it decodes to. Running locally means a token or an encoded secret is checked without being sent anywhere.
Using Base64 Validator
- Paste the Base64 string. Whitespace is ignored, so a value wrapped across lines is fine.
- The tool checks that every character is in the Base64 alphabet, that the length is a multiple of four, and that padding is correct.
- If it is valid, the tool reports how many bytes it decodes to; if not, it says whether the problem is a stray character, the length or the padding.
Where base64 validator helps
Spotting bad padding
A string that will not decode turns out to be missing its '=' padding; the validator says so.
Validation is only the first check
A valid Base64 string can decode to arbitrary bytes, including a damaged file. For example, SGVsbG8= represents Hello, but accepting that alphabet and padding does not verify a file signature or authenticate the sender. After validation, decode into the expected format and check its structure. Do not paste an access token merely to see whether its encoding is valid; use a harmless sample with the same structural problem.
Before you use the result
- It validates standard Base64. URL-safe Base64, which uses '-' and '_' instead of '+' and '/', will be flagged as containing invalid characters.
- A valid Base64 string is not necessarily meaningful - it confirms the encoding is well-formed, not that the decoded bytes are what you expect.
- Validation is one-way; there is no reverse of a check, unlike the encoders and decoders elsewhere on the site.
Questions about Base64 Validator
What makes Base64 invalid?
A character outside A–Z, a–z, 0–9, + and /; a length that is not a multiple of four; or wrong '=' padding. The tool says which.
Does it handle URL-safe Base64?
This validates standard Base64. URL-safe variants use '-' and '_', which are flagged as outside the standard alphabet.
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