Base64URL Decoder
The Base64URL Decoder converts any Base64URL-encoded string back into readable text — whether it is a JWT segment, a URL parameter or any other URL-safe encoded data.
What This Tool Does
Base64URL is the URL-safe variant of Base64: "+" becomes "-", "/" becomes "_" and padding "=" is omitted. JWTs use it for the header and payload. This tool reverses the encoding, restores padding automatically and prints the decoded content as text.
How to Use
- Paste a Base64URL string into the input field.
- The decoded text appears automatically.
- Copy or download the decoded output.
- Use Sample Data to load an example encoded string.
Key Features
- Decodes standard Base64URL including unpadded input
- Handles "-" and "_" URL-safe characters correctly
- Instant output as you type or paste
- Copy, download, sample and reset actions
- Useful for individual JWT header or payload segments
- Runs entirely client-side
Common Use Cases
- Decoding a single JWT segment copied from a log
- Reading URL-safe encoded parameters and tokens
- Debugging encoding issues between systems
- Learning the difference between Base64 and Base64URL
- Inspecting encoded data without writing a script
Base64 vs. Base64URL
Standard Base64 uses "+" and "/", which have special meaning in URLs. Base64URL (RFC 4648 §5) substitutes "-" and "_" and typically drops padding, making the output safe for URLs, filenames and HTTP headers.
Encoding is not encryption: Base64URL content is trivially reversible by anyone, so never use it to hide sensitive data.
Frequently Asked Questions
What is Base64URL encoding?
A URL-safe variant of Base64 that replaces "+" with "-", "/" with "_" and omits "=" padding. It is the encoding JWTs use for their segments.
Does the decoder handle missing padding?
Yes. Padding is restored automatically, so unpadded Base64URL strings decode correctly.
Can I decode a whole JWT with it?
Decode the segments individually — a full token contains dots that are not part of Base64URL. The JWT Decoder handles whole tokens in one step.
Why do I get garbled output?
The input may be standard Base64 (with "+" or "/") or not Base64 at all. Check the source encoding first.
Is Base64URL a form of encryption?
No. It is a reversible encoding with no key — anyone can decode it. Never treat encoded data as protected.
Is my input uploaded?
No. Decoding happens locally in your browser.
Related JWT Tools
- JWT Decoder — Decode JWT tokens to view header and payload
- JWT Payload Formatter — Pretty print JWT payload with proper indentation
- JWT Header Viewer — Display JWT header information only
- JWT Claims Viewer — View all JWT claims in a tree-style format