developer utility
Base64URL Decoder
Decode Base64URL strings — the URL-safe Base64 variant used inside JWTs and OAuth tokens, which swap + and / for - and _.
What is Base64URL Decoder?
Decode Base64URL strings — the URL-safe Base64 variant used inside JWTs and OAuth tokens, which swap + and / for - and _. Everything runs 100% client-side in your browser — no data is ever uploaded to a server, nothing is logged or stored, and the tool is completely free with no signup required.
Quick Answers
- Does this Base64URL decoder tool work offline?
- Once the page has loaded, yes. Encoding and decoding run entirely with browser-native JavaScript APIs, so no request ever leaves your device.
- Why does decoding sometimes fail with an error?
- Base64 strings must have a length that's a multiple of 4 (after padding) and only contain valid characters. Copy/paste errors, stray whitespace, or URL-safe variants (using - and _ instead of + and /) are the most common causes of decode failures.
- Is Base64 the same as encryption?
- No. Base64 is an encoding scheme, not encryption — it makes binary data safe to transmit as text, but anyone can decode it instantly with no key required. Never use Base64 alone to protect sensitive data.
All decoding happens entirely in your browser. No data is ever sent to a server — nothing you paste here is transmitted, logged, or stored.
Frequently asked questions
Does this Base64URL decoder tool work offline?
Once the page has loaded, yes. Encoding and decoding run entirely with browser-native JavaScript APIs, so no request ever leaves your device.
Why does decoding sometimes fail with an error?
Base64 strings must have a length that's a multiple of 4 (after padding) and only contain valid characters. Copy/paste errors, stray whitespace, or URL-safe variants (using - and _ instead of + and /) are the most common causes of decode failures.
Is Base64 the same as encryption?
No. Base64 is an encoding scheme, not encryption — it makes binary data safe to transmit as text, but anyone can decode it instantly with no key required. Never use Base64 alone to protect sensitive data.
Can I convert Base64 to a PDF, image or other file?
Yes in principle — a PDF or image sent as Base64 is just its raw bytes encoded as text, so decoding those bytes and saving them with the right extension (.pdf, .png, .zip…) recreates the file. This tool decodes Base64 into readable text, which is perfect for JSON, XML, config strings and UTF-8 payloads. Binary files contain null bytes that don't display, so for exact file recovery use a dedicated 'Base64 to file' converter or the file's own application.
Quick comparison
Base64 vs Base64URL — the difference that matters in URLs
Standard Base64 uses +, /, and = padding, which are problematic inside URLs. Base64URL swaps + and / for - and _, and strips padding, producing strings that are safe in URLs and filenames without percent-encoding.
| Aspect | Base64 (standard) | Base64URL |
|---|---|---|
| Characters | A-Z a-z 0-9 + / = | A-Z a-z 0-9 - _ |
| URL safety | Needs percent-encoding for + / = | Safe as-is in URLs and filenames |
| Padding | Uses = padding | Padding removed |
| Used by | Email, data URLs, generic encoding | JWTs, OAuth tokens, modern APIs |
| Interchange | Standard everywhere | Not interchangeable — must convert |
How to decode Base64URL in 3 steps
Base64URL is the URL-safe variant of Base64: it swaps + for - and / for _, and drops the = padding. JWTs use exactly this format for their header and payload segments.
- 1Paste a JWT segment or a Base64URL string. It may contain - and _ characters, which regular Base64 decoders reject.
- 2The tool decodes using the URL-safe alphabet automatically, so you do not need to convert anything by hand first.
- 3Copy the result. This is the same decoding applied to the middle segment of a JWT to read its payload.