Base64 Validator
Verify Base64 padding and character set, then preview decoded byte length and UTF-8 text when possible.
Check Base64 before you decode
Broken padding or stray characters cause confusing errors in APIs, JWT parsers, and data pipelines. Paste a candidate string to verify length rules, padding, and alphabet membership, then preview decoded byte length and UTF-8 text when the payload allows it.
Ready to transform data? Pair this checker with the Base64 Encoder or Base64 Decode tools on the site.
Frequently Asked Questions
Does valid Base64 always mean valid UTF-8 text?
No. Images, certificates, and compressed blobs decode to binary. The tool shows a UTF-8 preview only when the bytes form valid Unicode text.
Are URL-safe variants supported?
This validator expects standard Base64 with plus and slash symbols. URL-safe strings that use dashes and underscores should be normalized before validation.
Why must length be a multiple of four?
Base64 encodes three bytes into four characters. Padding equals signs restore that multiple when the source byte count is not divisible by three.
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