Foundations · January 2025

What does “decode” mean? A simple explanation for developers

In software, decode means transforming data from an encoded representation back into its original form. Here’s what that means across common developer workflows.

Decode meaning across Base64, URL, JWT, hex, and binary — Decode converts encoded text back to its original bytes or characters.

What “decode” means

Decoding reverses an encoding. The goal is to read or process the original data. Depending on the context, decoding may be purely mechanical (Base64) or involve validation logic (JWT).

Common decoding contexts

Base64: Convert Base64 text back to the original bytes. Typical for attachments or binary fields.
URL: Turn percent-encoded strings like %3A into characters (:).
JWT: Read the token’s header and payload (Base64URL). Note: decoding does not verify signatures.
Hex: Translate hexadecimal pairs (e.g., 48 65 6C 6C 6F) into readable text.
Binary: Map bits to characters using an encoding like ASCII or UTF-8.

Decode vs. encode

Encode prepares data for transport or storage (e.g., Base64 to avoid binary in JSON). Decode restores the original. They form a reversible pair when no information is lost.

When decoding fails

Input isn’t valid for the expected format (wrong alphabet or padding).
Wrong expectation about text encoding (UTF-8 vs. Latin-1).
JWT-specific: payload is readable, but signature isn’t verified—never accept unsigned tokens.

Try it in the Json

Paste any Base64 string, URL, JWT, hex, or binary into our online Json. Everything runs client-side, so no data leaves your browser.