#483 · Developer Tool

Base64URL Decoder

Decode padded or unpadded Base64URL into UTF-8 text and hex bytes. The validator rejects mixed or impossible alphabet and length combinations. Processing stays in the browser, so the input is not sent to a conversion service.

Developer Input

Base64URL value
Ad space

How to use this developer tool

  1. Paste base64url value or load the sample.
  2. Choose any format-specific option shown above the run button.
  3. Select Decode Base64URL or press Ctrl/Cmd + Enter.
  4. Review the summary and download the result if it matches your target format.

What this developer tool does

It normalizes the URL-safe alphabet and restores required padding before decoding bytes.

- and _ are mapped to + and /. A length remainder of 1 is impossible and is rejected.

JWT payload decoding does not validate a JWT signature.

Example

Input

SGVsbG8sIPCfjI0h

Run the included sample to see the exact output and byte statistics produced by the current options.

Use cases

  • Check values copied from email, URLs, tokens, or configuration files.
  • Prepare deterministic test fixtures without a server-side dependency.
  • Inspect byte-level transformations before adding them to application code.

Tips for reliable output

  • Keep the original input beside the result while debugging.
  • Confirm the alphabet or MIME variant expected by the receiving system.
  • Use hexadecimal output when bytes are not valid text.
  • Test Unicode and empty-edge cases in your own integration.
  • Do not treat reversible encoding as a security control.

Processing details

Strict UTF-8 decoding separates textual payloads from arbitrary binary data.

Whitespace and standard Base64 alphabet characters are rejected to avoid ambiguous input.

Frequently asked questions

What input does the Base64URL Decoder accept?

Base64URL value is accepted as plain text in the input area.

How does the Base64URL Decoder handle invalid data?

Whitespace and standard Base64 alphabet characters are rejected to avoid ambiguous input.

Is output from the Base64URL Decoder encrypted?

No. The transformation is an encoding or inspection operation, not encryption.

Can I use the Base64URL Decoder with Unicode text?

Yes. Text input is converted with UTF-8 where the format requires bytes.

What should I verify before using the result?

JWT payload decoding does not validate a JWT signature.

Format notes

PropertyValue
InputBase64URL value
RunsLocally in the browser

Encoding and Decoding tools

Browse byte viewers, Unicode inspectors, and text encoding converters in the same category.

View category