Free Base64 Encoder/Decoder Online

Base64 is the duct tape of the web. It is the encoding that lets you stuff binary data — images, fonts, certificates, file attachments — into places that only accept plain text, like JSON payloads, HTML attributes, CSS files, email MIME bodies, and URL query strings. Our free online Base64 Encoder / Decoder gives you a fast, no-fuss way to convert in either direction. Paste a string into the input box, pick Encode or Decode, and the result appears instantly in the output panel ready to copy. The conversion runs locally in your browser tab, which means even sensitive payloads (API tokens, signed JWTs, credential blobs, snippets of an OAuth response) never leave your device. There is no server round-trip, no logging, and no rate limit. The tool handles plain ASCII as well as full Unicode — UTF-8 multibyte characters like accented letters, emoji, Chinese, Cyrillic, and Arabic round-trip cleanly because the encoder converts text to UTF-8 bytes first and then to Base64, which is the standard most modern systems expect. For decoding, the tool accepts both standard Base64 and URL-safe Base64 (the variant that swaps `+` and `/` for `-` and `_`, used in JWT headers and S3 presigned URLs), and it tolerates input with or without padding `=` characters. Common scenarios this tool covers: turning a small image into a `data:image/png;base64,...` URI for embedding in CSS without an HTTP request; decoding the middle segment of a JWT to read the claims while debugging an auth bug; converting a credential string from a config file back to its plaintext form; preparing a binary blob for inclusion in a JSON request body; and round-tripping a Unicode string to make sure your encoding pipeline preserves it correctly. The output panel includes a length counter so you can see at a glance whether your encoded string fits inside a length-limited field (URL parameters and DNS labels both have limits). For developers debugging an API integration, this is the kind of tool you keep open in a tab next to your terminal. For students learning how data moves between systems, it is a quick way to see exactly what Base64 looks like at the character level — the alphabet of 64 ASCII characters, the padding rules, and how four output characters represent every three input bytes.

Three concrete examples this tool handles in seconds. (1) **Embedding a small icon in a CSS file**: convert the SVG/PNG to Base64, prefix with `data:image/png;base64,`, and paste into a `background-image` rule — one fewer HTTP request on page load. (2) **Debugging a JWT in a failing OAuth flow**: copy the middle segment from your auth header, paste it here, decode, and read the claims (`exp`, `iat`, `sub`, `aud`) to spot the wrong audience or expired token. (3) **Decoding a credential blob from a Kubernetes secret**: `kubectl get secret -o yaml` returns base64-encoded values; paste one in to verify the decoded password matches what you expect before you ship a deployment.

Why use this instead of `base64` on the command line or another website? The CLI tool (`base64` on macOS/Linux, `certutil -encode` on Windows) is excellent if you have a terminal open, but it has subtle gotchas around line wrapping and trailing newlines that bite people writing one-off pipelines. Many other web encoders quietly use UTF-16 internally, which corrupts non-ASCII inputs (paste an emoji and watch the round-trip break). This page uses UTF-8 on both sides, accepts both standard and URL-safe variants on input, and runs entirely locally so even sensitive payloads (tokens, secrets, signed claims) never reach a server. For related encoding work, the [HTML Encoder/Decoder](/tools/html-encoder) handles HTML entities (`&`, `<`, etc.), the [Character Encoding Converter](/tools/character-encoding) translates between UTF-8, ASCII, and ISO-8859-1, and the [JSON Formatter](/tools/json-formatter) is the right next stop after you decode a JWT payload and want to read the claims with proper indentation.