Free Online URL Encoder and Decoder
↑URL encoding, also known as percent-encoding, is a mechanism for translating unprintable or special characters in URLs to a universally accepted representation that is safe to transmit across the internet. When you type a URL into your browser or make an API request, certain characters such as spaces, ampersands, question marks, and non-ASCII characters must be converted into a format that web servers and browsers can interpret without ambiguity. Our free online URL encoder and decoder tool lets you perform these conversions instantly in your browser using the built-in JavaScript functions encodeURIComponent and decodeURIComponent, with no data ever sent to an external server.
How URL Encoding Works
↑The URL encoding standard, defined in RFC 3986, specifies that certain characters are reserved for special purposes within a URI structure. For example, the forward slash separates path segments, the question mark begins the query string, and the ampersand separates key-value pairs in query parameters. When these reserved characters need to appear as literal data rather than structural delimiters, they must be percent-encoded. Percent-encoding replaces each unsafe character with a percent sign followed by two hexadecimal digits representing the character's byte value in UTF-8. A space becomes %20, an ampersand becomes %26, and a plus sign becomes %2B. The encodeURIComponent function in JavaScript handles this transformation automatically, encoding all characters except unreserved characters defined as uppercase and lowercase letters, decimal digits, hyphens, underscores, periods, and tildes.
When to Use URL Encoding
↑Developers frequently need to encode URLs when constructing query strings dynamically, embedding user-supplied values into API endpoints, or passing data through redirect URLs. Without proper encoding, special characters in parameter values can break the URL structure, cause unexpected behavior, or introduce security vulnerabilities such as injection attacks. For example, if a search query contains an ampersand, failing to encode it would prematurely terminate that parameter and start a new one. Similarly, when building OAuth callback URLs or constructing deep links for mobile applications, the entire redirect URL must be encoded so it can safely travel as a single parameter value within another URL. This tool makes it easy to verify your encoded strings are correct before deploying them in production code.
Decoding Percent-Encoded URLs
↑URL decoding is the reverse process, converting percent-encoded sequences back into their original characters. This is essential when inspecting URLs copied from browser address bars, reading server logs, debugging webhook payloads, or parsing query strings received from external services. The decodeURIComponent function in JavaScript handles this conversion, interpreting each percent-encoded triplet and replacing it with the corresponding Unicode character. If the encoded string contains a malformed sequence, such as a percent sign not followed by two valid hexadecimal digits, the function throws a URIError. This tool catches such errors and displays a clear message so you can identify and fix the problematic input. All processing happens entirely on the client side, ensuring your data stays private and secure.