Base64 URL Encoder Decoder

Paste UTF-8 text or a URL-safe token into the Base64 URL Encoder Decoder below to convert between plain text and RFC 4648 Section 5 Base64URL with configurable '=' padding.

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Enter the inputs, then select Run Base64URL.

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How Base64 URL Encoder Decoder works

The Base64 URL Encoder Decoder converts your input string into a UTF-8 byte array, encodes 24-bit groups into 6-bit symbols using the URL-safe alphabet (A-Z, a-z, 0-9, '-', '_'), and either strips or preserves '=' padding.

Index 62: '+' -> '-'; Index 63: '/' -> '_'; Unpadded length = ceil(UTF8_bytes * 4 / 3).

Side-by-side cards show both the Base64URL string and the standard Base64 equivalent so you can spot exactly which characters were substituted.

Base64 URL Encoder Decoder workflow overview — Workflow overview for Base64 URL Encoder Decoder.

Base64 URL Encoder Decoder Quick Reference & Input Guide

Review the input parameters, allowed value ranges, and worked reference cases for the Base64 URL Encoder Decoder below before running your calculation.

Parameter / Scenario	Default / Sample Value	Rule or Allowed Range	Output / Usage Note
Input: Operation mode	encode	Options: Encode UTF-8 text -> Base64URL, Decode Base64URL -> UTF-8 text	Required workspace parameter
Input: Input string	https://aitoolsfree.net/tools/?q=...	Input text or Base64URL payload.	Required workspace parameter
Input: Padding ('=') policy when encoding	unpadded	Options: Omit '=' padding (RFC 7515 JWT / URL-safe default), Keep '=' padding (4-character block alignment)	Required workspace parameter
Worked Case 1: Encoding a URL with query parameters (46 UTF-8 bytes)	Preloaded / test values	Base64URL(bytes) = StandardBase64(UTF8(text)).replace('+', '-').replace('/', '_').rstrip('=')	Encoding 'https://aitoolsfree.net/tools/?q=a+b&mode=full' yields 62 unpadded Base64URL characters ('aHR0cHM6Ly9haXRvb2xzZnJlZS5uZXQvdG9vbHMvP3E9YStiJm1vZGU9ZnVsbA') vs. 64 padded characters ending in '=='.
Worked Case 2: Decoding an unpadded JWT payload segment	Preloaded / test values	Base64URL(bytes) = StandardBase64(UTF8(text)).replace('+', '-').replace('/', '_').rstrip('=')	Switching to Decode mode and pasting 'eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIn0' restores the missing '=' padding and outputs '{"sub":"1234567890","name":"John Doe"}'.

How to use Base64 URL Encoder Decoder step by step

Encode URL parameters, OAuth state strings, or decode JWT header/payload segments locally.

Select Encode or Decode mode

Pick 'Encode UTF-8 text -> Base64URL' or 'Decode Base64URL -> UTF-8 text'.

Run Base64URL

Base64 URL Encoder Decoder step 1: Select Encode or Decode mode — Step 1 workflow overview for Base64 URL Encoder Decoder.

Paste your UTF-8 string or Base64URL token

Paste the raw text, JSON object, or URL-safe Base64 token into the input box.

Run Base64URL

Base64 URL Encoder Decoder step 2: Paste your UTF-8 string or Base64URL token — Step 2 workflow overview for Base64 URL Encoder Decoder.

Choose padding policy and copy the result

Select Omit '=' padding (standard for JWTs and URLs) or Keep '=' padding, then click Run Base64URL.

Run Base64URL

Base64 URL Encoder Decoder step 3: Choose padding policy and copy the result — Step 3 workflow overview for Base64 URL Encoder Decoder.

Worked examples for Base64 URL Encoder Decoder

See how URL query strings and JWT payloads convert cleanly without percent-encoding issues.

Encoding a URL with query parameters (46 UTF-8 bytes)

Encoding 'https://aitoolsfree.net/tools/?q=a+b&mode=full' yields 62 unpadded Base64URL characters ('aHR0cHM6Ly9haXRvb2xzZnJlZS5uZXQvdG9vbHMvP3E9YStiJm1vZGU9ZnVsbA') vs. 64 padded characters ending in '=='.

Run Base64URL

Base64 URL Encoder Decoder example 1: Encoding a URL with query parameters (46 UTF-8 bytes) — Worked example 1 for Base64 URL Encoder Decoder.

Decoding an unpadded JWT payload segment

Switching to Decode mode and pasting 'eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIn0' restores the missing '=' padding and outputs '{"sub":"1234567890","name":"John Doe"}'.

Run Base64URL

Base64 URL Encoder Decoder example 2: Decoding an unpadded JWT payload segment — Worked example 2 for Base64 URL Encoder Decoder.

Inspecting '+' and '/' substitutions

The breakdown cards count how many '+' and '/' symbols from standard Base64 were replaced with '-' and '_' in Base64URL.

Run Base64URL

Base64 URL Encoder Decoder example 3: Inspecting '+' and '/' substitutions — Worked example 3 for Base64 URL Encoder Decoder.

How to interpret the Base64 URL Encoder Decoder output

Compare the unpadded Base64URL output, padded Base64URL output, and standard Base64 output.

The main result displays the converted string. Breakdown cards report UTF-8 byte length, output character length, padding characters stripped/restored, and URL-safe symbol replacements ('-' and '_').

Run Base64URL

How to interpret Base64 URL Encoder Decoder results — Result interpretation guide for Base64 URL Encoder Decoder.

Input limits, assumptions, and related tools

Verify character validity and encryption vs. encoding boundaries.

Base64URL is an encoding scheme, not encryption; anyone can decode a Base64URL string without a key. In Decode mode, inputs with length % 4 == 1 or characters outside [A-Za-z0-9-_+/=] are rejected with a validation error.

Run Base64URL

Scope limits and assumptions for Base64 URL Encoder Decoder — Assumptions and input boundaries for Base64 URL Encoder Decoder.

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Base64 URL Encoder Decoder: common questions

Answers about using Base64 URL Encoder Decoder and understanding its results.

How does Base64URL differ from standard Base64?

Standard Base64 (RFC 4648 Section 4) uses '+' at index 62, '/' at index 63, and '=' for padding, all of which have special meanings in URLs and filenames. Base64URL (Section 5) replaces '+' with '-' (hyphen) and '/' with '_' (underscore), and typically omits trailing '=' padding.

Why do JWTs (JSON Web Tokens) use unpadded Base64URL?

RFC 7515 (JSON Web Signature) specifies unpadded Base64URL so tokens can be passed safely inside HTTP query parameters, Authorization headers, and URL paths without percent-encoding.

How does this tool handle multi-byte UTF-8 characters like emojis or accented letters?

Unlike window.btoa() alone, which throws an error on non-Latin1 characters, this tool encodes text to UTF-8 bytes via TextEncoder before applying the Base64URL alphabet, and decodes via TextDecoder('utf-8').

Can the decoder read a Base64URL string that has no '=' padding at the end?

Yes. In Decode mode, the parser automatically calculates the modulo-4 remainder (length % 4) and restores the required '=' padding before decoding.

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Run Base64URL