Base64 Encode & Decode — Mac, Linux, Windows, Browser (Quick Reference)

Platform Quick Reference

Task	Mac / Linux	Windows (PowerShell)
Encode text	echo -n "text" | base64	[Convert]::ToBase64String([Text.Encoding]::UTF8.GetBytes("text"))
Decode text	echo "dGV4dA==" | base64 -d	[Text.Encoding]::UTF8.GetString([Convert]::FromBase64String("dGV4dA=="))
Encode file	base64 file.png	[Convert]::ToBase64String([IO.File]::ReadAllBytes("file.png"))
Decode to file	base64 -d encoded.txt > file.png	[IO.File]::WriteAllBytes("file.png",[Convert]::FromBase64String($b64))

Note: Mac uses base64 -D (capital D) for decode, while Linux uses base64 -d (lowercase). This trips up everyone switching between systems.

Don't want to remember terminal syntax? The browser-based Base64 tool works on every platform — paste text or drop a file, get the result instantly.

When You Actually Need Base64

• Debugging API auth headers — the Authorization: Basic dXNlcjpwYXNz header is Base64. Decode it to see the credentials: user:pass. Use the Base64 tool or the JWT Decoder for full JWT tokens.
• Embedding images in CSS/HTML — small icons (under 5KB) as data:image/png;base64,... save HTTP requests. Encode the image file to get the Base64 string.
• Email debugging — MIME email attachments are Base64-encoded. Decode to recover the original file.
• Storing binary in JSON/XML — these formats only support text. Binary data (files, images) must be Base64-encoded to fit.

Common Gotchas

• Newlines in terminal output — echo "text" | base64 encodes a trailing newline. Use echo -n "text" | base64 to avoid it. This causes subtle bugs when encoding API credentials.
• URL-safe vs standard Base64 — standard Base64 uses + and / which break URLs. Base64URL uses - and _ instead. JWTs use Base64URL. The browser tool auto-detects which variant you paste.
• Padding (=) — Base64 output is padded with = to make the length a multiple of 4. Some systems strip padding. The tool handles both padded and unpadded input.
• It is NOT encryption — Base64 is trivially reversible. Anyone can decode it. Never use Base64 to "hide" sensitive data. Use the Text Encryptor (AES-256) for actual security.

Browser Tool vs Terminal — When to Use Each

Use the terminal when you are already in the command line (scripting, piping output, CI/CD). The one-liners above are fastest when you are already in a shell session.

Use the browser tool when:

• You want to encode/decode files (drag and drop vs remembering file I/O syntax)
• You are on a machine without terminal access (Chromebook, locked-down corporate laptop)
• You want to decode something without it appearing in your shell history (passwords, API keys)
• You are debugging a JWT — the JWT Decoder parses all three sections and converts timestamps