URL Encoder / Decoder: Frequently Asked Questions

encodeURI encodes a complete URL, preserving structural characters like /, :, ?, and &. encodeURIComponent encodes a single value for use inside a URL, encoding everything including /, :, ?, and &. Use encodeURIComponent for parameter values; use encodeURI only for full URLs that need light sanitisation.

In query strings, HTML form submission encodes spaces as +. RFC 3986 percent-encoding uses %20. Both are widely accepted in query strings. In URL paths, only %20 is valid — a + in a path is a literal plus sign.

Double-encoding occurs when an already-encoded string is encoded again, turning %20 into %2520 (because % itself is encoded as %25). Always decode first to check if a string is already encoded before encoding it.

The @ in an email address does not need encoding in the mailto: address itself (mailto:user@example.com is valid). But if you pass the email as a query parameter value (e.g., ?to=user@example.com), the @ must be encoded as %40.

Unreserved characters that never need encoding: A–Z, a–z, 0–9, hyphen (-), period (.), underscore (_), tilde (~). Reserved characters are safe only in their structural positions (/ in paths, & between parameters) — as data values they must be encoded.

Browsers implement URL normalisation differently. Chrome may encode some characters that Firefox leaves unencoded, and vice versa. Both produce equivalent URLs that servers should handle identically, but the visual representation in the address bar differs.