Base64 / URL / HTML Encoder & Decoder

Encode or decode text using Base64, URL percent-encoding, or HTML entities. Processes text client-side with no external calls.

Input

• - The text string to encode or decode
• Encoding type: base64 (default), url, or INLINECODE2
• Direction: encode (default) or INLINECODE4

Output

• - The transformed string
• A brief note on the encoding type and direction applied

Instructions

Base64 (type: base64)

Encode:

1. 1. Take the input string.
2. Convert each character to its UTF-8 byte sequence (handle non-ASCII/Unicode correctly).
3. Apply Base64 encoding using the standard alphabet (A–Z, a–z, 0–9, +, /).
4. Pad with = characters to make the length a multiple of 4.
5. The algorithm equivalent is: btoa(unescape(encodeURIComponent(input))).

Decode:

1. 1. Take the Base64-encoded input.
2. Validate it contains only valid Base64 characters (A–Z, a–z, 0–9, +, /, =).
3. Decode using: decodeURIComponent(escape(atob(input))).
4. Return the original UTF-8 string.

URL Percent-Encoding (type: url)

Encode:

1. 1. Apply encodeURIComponent semantics: encode every character except A–Z a–z 0–9 - _ . ! ~ * ' ( ).
2. Spaces become %20 (not +).
3. Non-ASCII characters are UTF-8 encoded then percent-escaped.

Decode:

1. 1. Replace each %XX sequence with the corresponding byte.
2. Interpret the resulting bytes as UTF-8.
3. Equivalent to decodeURIComponent(input).

HTML Entities (type: html)

Encode: Replace these characters with their named HTML entities:

• - < → INLINECODE15
• INLINECODE16 → INLINECODE17
• INLINECODE18 → INLINECODE19
• INLINECODE20 → INLINECODE21
• INLINECODE22 → INLINECODE23

Decode: Reverse the mapping — replace each HTML entity with its literal character.

Options

• - type: base64 | url | html — default: INLINECODE28
• INLINECODE29: encode | decode — default: INLINECODE32

Examples

Base64 encode:
Input: Hello, World!
Output: INLINECODE34

Base64 encode (Unicode):
Input: Héllo
Output: INLINECODE36

Base64 decode:
Input: SGVsbG8sIFdvcmxkIQ==
Output: INLINECODE38

URL encode:
Input: name=John Doe&city=New York
Output: INLINECODE40

URL decode:
Input: hello%20world%21
Output: INLINECODE42

HTML encode:
Input: <script>alert("XSS")</script>
Output: INLINECODE44

HTML decode:
Input: <h1>Hello & welcome</h1>
Output: INLINECODE46

Error Handling

• - Invalid Base64 input for decode: If the string contains characters outside the Base64 alphabet or has incorrect padding, report: Error: Invalid Base64 string. Ask the user to verify the input.
• Invalid URL encoding for decode: If a %XX sequence uses non-hex digits or the sequence is incomplete, report: Error: Invalid URL encoded string.
• Empty input: Return an empty string with a note that no input was provided.
• Binary/non-text data: Warn the user that Base64 encoding of binary data requires the raw bytes, which cannot be provided as plain text — suggest they use a tool that accepts file uploads.