Use a browser-based Base64 tool that encodes or decodes the text instantly on your own device. That matters more than it sounds, because the strings developers decode are often Basic auth headers, tokens or config secrets, exactly the things you should never paste into a site that processes them server-side.
Base64 maps binary data onto 64 printable characters so it can travel safely through text-only channels like HTTP headers, JSON strings and data URIs. Anyone can reverse it instantly, so it provides zero secrecy, and the encoded form is about a third larger than the original. If you see a long string ending in one or two equals signs, it is very often Base64.
A Basic auth header is literally username:password in Base64, and JWT segments, API payloads and Kubernetes secrets are Base64 too. Decoding those on a website that sends the input to its server means handing over a live credential. A client-side tool does the encoding and decoding in your browser, so the string never leaves your machine.
No. It is an encoding, not encryption, and anyone can decode it instantly. Never use it to protect secrets.
No. Encoding and decoding run entirely in your browser.
Base64 represents every 3 bytes as 4 characters, so output is roughly 33 percent larger than the input.