JWT Decoder vs Base64 Encoder
Choose this if
you are looking at a token and want the claims read out, with the expiry checked against now
Choose this if
you have one Base64 string, or are encoding rather than decoding
How they compare
| Criterion | JWT Decoder | Base64 Encoder and Decoder |
|---|---|---|
| Handles the three-part structure | Splits on the dots and decodes the header and payload separatelyBetter here | Treats the whole thing as one string and fails on the dots |
| Padding | Restores it automatically: JWT segments drop it by convention | Restores it too, though many Base64 tools reject unpadded input outright |
| Claim meanings | Labels the registered claims: iss, sub, aud, exp, nbf, iat, jtiBetter here | None. You get raw JSON and interpret it yourself |
| Timestamps | Converts exp, iat and nbf to readable UTC dates and says whether the token has expiredBetter here | Shows a ten-digit number |
| Breadth of use | Tokens only | Any Base64 at all, and it encodes as well as decodesBetter here |
Which is best for you
Use the JWT decoder when debugging authentication
An API is rejecting a token and you need to see what it actually claims. The decoder splits the segments, pretty-prints both JSON objects, explains what each registered claim means, and converts the expiry to a real date compared against your clock. Doing that with a Base64 decoder means three separate operations and mentally converting Unix timestamps.
Use the Base64 tool for everything that is not a token
Decoding a data URI, reading a Base64-encoded config value, encoding text for an email header, or checking what a particular string decodes to. It handles Unicode correctly in both directions and offers the URL-safe alphabet, which is, incidentally, exactly the alphabet a JWT uses.
The recommendation
Use the JWT decoder for tokens. You can absolutely decode the segments individually with a Base64 tool, and it is a useful thing to understand, but doing it by hand means splitting on dots, decoding twice, and converting Unix timestamps in your head, every time. The more important point is one both tools should make you aware of: decoding is not verifying. Anyone holding a JWT can read its payload, so nothing confidential belongs in one.
Frequently asked questions
Is a JWT encrypted?
No. The header and payload are Base64url-encoded, which is a transport encoding with no key. That is exactly why a plain Base64 decoder can read them. Never put anything confidential in a JWT payload. If the contents must be hidden you need JWE, which is a different specification.
Why does Base64 decoding a JWT segment sometimes fail?
Because JWT uses the URL-safe alphabet and drops the padding. Segments contain - and _ where standard Base64 has + and /, and the trailing equals signs are gone. A decoder that does not restore the padding and translate the alphabet will refuse the input.
Can either tool tell me whether a token is genuine?
Neither. Verifying a signature needs the signing secret or public key, which belongs on your server and must never be pasted into a web page. Both tools show you what a token claims; only your server can establish whether the claims are trustworthy.