Decode Base64 and check whether the result is valid JSON
Base64 to JSON decodes an encoded text payload so you can inspect the underlying document. It verifies both the transport encoding and JSON syntax.
When should you use it?
- Inspect a Base64 field from an API response.
- Check whether encoded content is actually JSON.
- Recover a readable document for debugging.
Example: inspect an encoded document
The decoded bytes must be valid UTF-8 and a complete strict JSON document.
eyJhIjoxfQ=={"a":1}Decoding has three separate checks
The input must use the accepted standard Base64 form, the decoded bytes must be valid UTF-8, and that text must parse as strict JSON. Failure at any stage means a different problem. For example, a Base64-encoded image can be valid Base64 without being JSON. Check the producer and the expected content before trying to repair the decoded text.
Check for wrappers and different encodings
Paste the encoded value itself rather than a surrounding data URL or an entire JWT. JWT segments use Base64url conventions and have a dedicated decoder on this site. If a field contains another encoding layer after decoding, identify that contract explicitly instead of repeatedly decoding until the output happens to look readable.
How do I decode a Base64 field and verify that it contains JSON?
Paste standard padded Base64 text. The decoder checks the alphabet and padding, decodes bytes as UTF-8, and then validates the resulting text as one strict JSON value. A successful result is formatted for reading.
Base64 input and decoded JSON
texteyJhIjoxfQ== → {"a":1}A binary file or ordinary prose can be valid Base64 but still fail the UTF-8 or JSON check.
Why does a JWT segment fail here?
JWTs use base64url and often omit padding. This tool expects standard padded Base64; use JWT Decoder for compact tokens.
What should you check before using the result?
Arbitrary binary, invalid UTF-8, or plain text that is not JSON will fail. Decoding does not prove who created or transmitted the original data.
Understand JSON syntaxTechnical reference: Base64 alphabets and padding · RFC 4648