# encode(_:) Encodes raw bytes using the URL-safe unpadded Base64 alphabet. ``` static func encode(_ data: Data) -> String ``` ## Parameters `data` The bytes to encode. May be empty; the empty input produces the empty string. ## Return Value A Base64URL string consisting solely of characters from the 64-symbol URL-safe alphabet plus no padding. Round- tripped via [`decode(_:)`](/documentation/OpenSSL/Base64URL/decode(_:)) to recover the original bytes. ## Discussion Emits the encoding defined in [RFC 4648 §5](https://datatracker.ietf.org/doc/html/rfc4648#section-5): the standard Base64 alphabet with `+` replaced by `-`, `/` replaced by `_`, and the trailing `=` padding stripped. The output is safe to drop into URL path segments, query parameter values, HTTP header fields, JSON string values, JWS/JWT segments, and filename components without further escaping. Implementation detail: this is a thin layer over Foundation’s `Data.base64EncodedString()` followed by alphabet translation and padding removal. It does not call into `libcrypto`. > Note: Not constant-time with respect to the input length or > content. Do not use on side-channel-sensitive material.