Question 1

What is this tool used for?

Accepted Answer

This tool is primarily used for inspecting JWT (JSON Web Token) payloads and debugging Base64-encoded API responses. Many authentication systems and APIs encode structured JSON data as Base64 to make it URL-safe or to fit it into a header field. Pasting the Base64 segment here reveals the underlying JSON in a readable, formatted view.

Question 2

What happens if the decoded value is not valid JSON?

Accepted Answer

If the Base64 string decodes to something that is not valid JSON, the tool shows the raw decoded text along with a notice that the result is not parseable as JSON. This can happen when the Base64 string contains plain text, binary data, or a different structured format such as XML or CSV.

Question 3

How do I decode a JWT payload with this tool?

Accepted Answer

A JWT has three segments separated by dots: header.payload.signature. Copy only the middle segment (the payload) and paste it into this tool. The payload uses URL-safe Base64 without padding, so you may need to add = characters at the end. Add one or two = characters until the string length is divisible by 4, then decode. The result is the JSON claims object containing fields like sub, iat, exp, and any custom claims.

Question 4

Does decoding change the order of JSON keys?

Accepted Answer

The order of keys in the decoded JSON matches the order in the original JSON that was encoded. JSON itself does not guarantee key order, but in practice most serializers preserve insertion order. The formatter displays keys in the order they appear in the decoded string, so what you see reflects what was actually encoded.

Base64 to JSON Converter

Frequently asked questions

More JSON Tools

About Base64 to JSON Decoding