URL Encoder / Decoder (percent-encoding, UTF-8 safe)
Use to embed text safely in URLs, query parameters, or form data. Handles spaces, special characters, and Unicode (including CJK and emoji) correctly.
How it works
What URL encoding is
URLs are restricted to a small set of ASCII characters. To include anything else — spaces, accents, Chinese characters, emoji, special symbols — you replace each unsafe byte with %XX where XX is its hexadecimal byte value. A space becomes %20, a slash %2F, the kanji 漢 becomes %E6%BC%A2 (its UTF-8 bytes percent-encoded).
This calculator uses the browser's built-in encodeURIComponent and decodeURIComponent. It encodes everything that isn't an unreserved character (letters, digits, -._~), which is the right behavior for query parameters and form data.
encodeURI vs encodeURIComponent
JavaScript has two encoders. encodeURI leaves URL structure characters (/ ? & # = + etc.) alone — use it on a full URL. encodeURIComponent escapes all of those — use it on the value inside a query parameter.
This tool uses encodeURIComponent, the safer choice for embedding arbitrary text into a URL. If you have a full URL with structure you want to preserve, encode only the parts that need it.
Common gotchas
Plus sign in URLs. Some servers treat '+' as a space (a legacy from form encoding). encodeURIComponent leaves '+' alone, but a server might decode it to space. To be safe, replace '+' with %2B if you're sending it as data.
Double encoding. Encoding an already-encoded string adds another layer (% becomes %25, so '%20' becomes '%2520'). Always check whether the input is already encoded before running encode again.
Length increase. UTF-8 multi-byte characters expand to 3-4 percent-codes each. A 100-character Japanese string easily becomes a 900+ character URL.
Frequently asked questions
›Why isn't my space '%20' decoding to space?
It should — but if you have '+' in a URL it might also represent space (legacy form encoding). Replace + with space first if needed.
›Does this handle emoji?
Yes. Emoji are encoded as their UTF-8 byte sequences (typically 4 bytes / 4 percent-codes per emoji).
›What's the difference between URL encoding and HTML encoding?
URL encoding uses % notation for URL contexts. HTML encoding uses < > etc. for HTML. Different contexts, different rules.
›When should I encode and when not?
Encode any value going into a URL query parameter, path segment containing user input, or form data. Don't encode an already-built URL — that double-encodes.
›Why does '%' in my decoded text cause an error?
A bare '%' followed by something that isn't valid hex is invalid percent-encoding. Encode '%' to '%25' before including it in a URL.
›Does the browser do this automatically?
Yes — when building URLs via URL or URLSearchParams APIs. This tool exposes the same logic for ad-hoc use.
›What characters are 'safe' and don't need encoding?
Letters (A-Z, a-z), digits (0-9), and these: - . _ ~ . Everything else gets percent-encoded by encodeURIComponent.
›Does the data leave my browser?
No. Encoding and decoding both run locally.
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