URL Decode Online (Live Percent-Decoder & Query Tool)

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Decode percent-encoded URLs, query string parameters, and API endpoints back into readable plain text. Automatically normalize + signs into spaces, safely recover truncated UTF-8 characters, unroll double-encoded strings, and inspect query parameters in a real-time table.

How Do You Decode a Percent-Encoded URL?

To decode a percent-encoded URL, locate every percent triplet (%XX) and convert the two hexadecimal digits back into their corresponding ASCII or UTF-8 byte. The browser reassembles these bytes into original text (e.g., %20 decodes to a space, %26 to an ampersand &, and %3D to an equals sign =).

Encoded URL / Query String Input: 78 characters

https%3A%2F%2Fexample.com%2Fsearch%3Fquery%3DWeb%20Tools%2BUtilities%26sort%3Dasc

Decode + as spaces (Form-encoded standard) Recursive decode (Unrolls double-encoded %2520)

Decoded Plaintext URL: Decoded Successfully

Ready

Extracted Query Parameters:

Parameter Key	Decoded Value

Malformed Sequence: The input contains incomplete percent triplets. Resilient parsing was applied to decode all valid characters.

How Percent-Decoding Works Under RFC 3986

Under RFC 3986, web browsers and HTTP proxy servers convert reserved and non-ASCII characters into hexadecimal triplets for transmission.

The decoding process reverses this operation:

1. Identify Percent Markers (%): The parser scans the string for the percent character delimiter.
2. Parse Hexadecimal Pairs: The two characters immediately following the % are read as an 8-bit base-16 number (e.g., 20 in hex is $2 \times 16 + 0 = \mathbf{32}$ in decimal, matching the ASCII space code).
3. Reconstruct UTF-8 Multibyte Sequences: For characters that span multiple bytes (such as accents or emojis), the decoder reads consecutive percent triplets (e.g., %C3%A9 → 0xC3 0xA9) and resolves them through the UTF-8 character table into a single character (é).

Common Percent-Encoded Triplets Reference Matrix

Character	Decoded Symbol	Percent-Encoded Triplet	URI Syntactic Role
Space	(space)	%20 or +	Word separation in query strings
Ampersand	&	%26	Separates multiple query parameters
Equals Sign	=	%3D	Assigns values to parameter keys
Question Mark	?	%3F	Indicates the start of query parameters
Forward Slash	/	%2F	Hierarchical path segment delimiter
Hash / Fragment	#	%23	Indicates anchor or client-side fragment

Double-Encoded URLs: How `%2520` Happens

A frequent architectural issue in web applications is double percent-encoding. This occurs when an already encoded URL passes through a secondary proxy, redirect handler, or API router that encodes the string again:

Original String:      "Hello World"
Single-Encoded:       "Hello%20World"
Double-Encoded:       "Hello%2520World"  (• The '%' of '%20' became '%25'!)

Standard decoders decode %2520 into %20 and stop. By enabling the "Recursive decode" checkbox in this tool, the engine applies iterative unrolling to restore the true underlying plaintext automatically.

Related URL & Encoding Utilities:

• URL Percent-Encoding Converter — Encode query parameters under RFC 3986 with encodeURIComponent vs. encodeURI options.
• Full URL Converter Hub — Master URL encoder and decoder.
• SEO URL Slug Generator — Convert headlines into lowercase, hyphenated URL permalinks.
• HTML Entity Converter — Escape DOM markup characters to prevent XSS.
• HTML Entities vs. URL Encoding Guide — Technical comparison of web encoding standards.

Frequently Asked Questions

How do I decode a URL with plus signs (+) instead of %20?

Keep the "Decode + as spaces" checkbox enabled. HTML form submissions use the application/x-www-form-urlencoded format, which replaces spaces with plus signs rather than %20. Our tool normalizes these into standard spaces automatically.

What causes a "URI malformed" error during URL decoding?

A "URI malformed" error occurs when a percent symbol (%) is not followed by two valid hexadecimal digits (0-9, A-F), or when a multibyte UTF-8 sequence is truncated. Our tool applies resilient parsing to prevent crashes.

How do I decode a double-encoded URL?

Enable the "Recursive decode" checkbox. The engine will iteratively unroll nested percent sequences (such as %2520 into spaces) until the underlying plaintext is reached.

Can this tool extract query parameters from a URL?

Yes. When you paste an encoded URL containing a query string (?key=value), the tool automatically parses and displays each parameter key and decoded value in an interactive table beneath the output.

Is my URL data logged or stored on a server?

No. All URL parsing, parameter extraction, and percent-decoding execute 100% locally inside your browser's runtime memory using JavaScript. No URLs, query parameters, or tokens are ever sent across a network or saved to any database.