Percent-Encoding Decoder

Percent-encoding, also known as URL encoding, is a mechanism for encoding information in a Uniform Resource Identifier (URI) under certain circumstances. Characters that are not allowed in a URI - such as spaces, non-ASCII characters, and characters with special meaning like ?, &, #, and %itself - are replaced with a %character followed by two hexadecimal digits representing the character's byte value. For example, a space character (ASCII 32, hex 20) is encoded as %20. The + character is also used as a space replacement in application/x-www-form-urlencoded form data (the HTML form encoding standard), where spaces in form field values are encoded as + rather than %20. Percent-encoding is defined by RFC 3986 (Uniform Resource Identifier) and is universally supported by all web browsers, servers, and HTTP libraries.

• %20 (Space): The most common percent-encoded character. Spaces are not allowed in URLs, so every space in a URL or query parameter must be encoded. In form data, spaces may also be encoded as +.
• %21 to %2F (Punctuation): Characters like ! (%21)," (%22), # (%23),$ (%24), % (%25), &(%26), ' (%27), ( (%28),) (%29), * (%2A), +(%2B), , (%2C), and / (%2F).
• %3A to %40 (More Punctuation): Including : (%3A),; (%3B), < (%3C),= (%3D), > (%3E),? (%3F), and @ (%40).
• %5B to %60 and %7B to %7E: Bracket characters [ (%5B),\\ (%5C), ] (%5D), ^(%5E), ` (%60), { (%7B),| (%7C), } (%7D), and ~(%7E).
• Multi-byte UTF-8 Sequences: Non-ASCII characters (Unicode) are first encoded as UTF-8 bytes, then each byte is percent-encoded. For example, the Euro sign € (U+20AC) encodes as %E2%82%AC (3 bytes), and emoji like 😀 (U+1F600) encode as %F0%9F%98%80 (4 bytes). Our tool automatically detects and decodes these multi-byte sequences.

1. Input Scanning: The tool scans every character in your input text, identifying %XX sequences (where X is a hexadecimal digit 0-9 or A-F) and+ characters. Each %XX sequence is validated for proper hex format, and malformed sequences are flagged and passed through as literals.
2. Multi-byte UTF-8 Detection: After finding a valid %XX byte, the tool checks if it forms a multi-byte UTF-8 sequence by examining subsequent bytes. A byte in the range 0xC0-0xDF starts a 2-byte sequence, 0xE0-0xEFstarts a 3-byte sequence, and 0xF0-0xF7 starts a 4-byte sequence. If the following bytes are valid continuation bytes (0x80-0xBF), the full Unicode code point is decoded. Otherwise, each byte is decoded individually.
3. Segmentation & Analysis: Each character in the output is tagged with metadata: whether it was encoded or literal, the original encoded representation, its Unicode code point, and a human-readable character name. Identical encoding patterns are grouped and counted, providing a comprehensive picture of what was encoded and how often.

Our Percent-Encoding Decoder processes everything locally in your browser. Text input and uploaded files are read using the browser's APIs and analyzed entirely in memory - no data is ever uploaded to any server. The tool is 100% free with no signup, no account, and no usage limits.

Supported input: Text pasted directly or uploaded from files (.txt, .html, .htm, .url, .csv, .xml, .json, .md) up to 10 MB. The tool detects both single-byte percent-encoding and multi-byte UTF-8 percent-encoding sequences. It also handles the+ to space conversion used in application/x-www-form-urlencoded form data.

Limitations: The tool decodes percent-encoding only - it does not encode text. For encoding, use a dedicated URL encoder. Very large files (over 10 MB) may cause browser memory issues. Binary files that are not valid UTF-8 may produce replacement characters (U+FFFD) when decoded as text. The character breakdown display shows up to 1,000 characters for performance.