Base64 Encoder & Decoder
Encode text or files to Base64 and decode Base64 back to text — side by side, live. URL-safe Base64 (RFC 4648), MIME line wrapping (76 chars, RFC 2045), file drag-and-drop, data URI auto-strip and encode-each-line mode. 100% client-side.
Base64 Encoder and Decoder Tool
URL-safe Base64, MIME wrap, file encode, data URI strip — features most Base64 tools skip
Most Base64 tools offer one text box and a button. This tool gives you a live split-view with simultaneous encode and decode, URL-safe Base64 for JWT and web APIs, MIME line wrapping for email and PEM, file drag-and-drop, and automatic data URI prefix stripping for one-click decoding of image embeds.
data:image/png;base64,iVBOR... into the Base64 panel, the decoder automatically strips the prefix before decoding. No manual editing needed.How to encode and decode Base64 online
Base64 variants and when to use them
| Variant | Characters used | Standard | Use case |
|---|---|---|---|
| Standard | A-Z a-z 0-9 + / = | RFC 4648 §4 | General encoding, data storage, HTML data URIs |
| URL-safe | A-Z a-z 0-9 - _ (no padding) | RFC 4648 §5 | URL query params, cookies, filenames, JWT tokens |
| MIME (76-char wrap) | Standard + CRLF every 76 chars | RFC 2045 | Email attachments, MIME content encoding |
| PEM (64-char wrap) | Standard + newline every 64 chars | RFC 7468 | TLS certificates, SSH keys, PGP blocks |
| Each line separately | Standard per line | Custom | Multiple independent values, one per line input |
Base64 Encoder & Decoder — A Complete Guide
Base64 is a binary-to-text encoding scheme that represents binary data as a string of ASCII characters. It converts every three bytes of binary data into four printable characters from a 64-character alphabet: A–Z, a–z, 0–9, + and /. The result is approximately 33% larger than the original data but safe to transmit through any text-based medium — email, JSON, XML, HTTP headers, URLs — without binary data being corrupted or misinterpreted.
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Base64 appears in almost every part of modern web and application development. HTML data URIs use Base64 to embed images directly in CSS and HTML without a separate file request. JWT tokens (JSON Web Tokens) use URL-safe Base64 to encode their header and payload. HTTP Basic Authentication encodes credentials as Base64 in the Authorization header. SMTP email attachments are Base64-encoded by MIME. TLS certificates, SSH keys and PGP blocks use PEM format — Base64 with 64-character line wrapping. API payloads that need to transmit binary data (images, audio, documents) often encode them as Base64 strings inside JSON.
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Standard Base64 uses two characters that have special meaning in URLs: “+” (which URL-encodes as %2B) and “/” (which URL-encodes as %2F). The “=” padding character also causes issues in some URL contexts. URL-safe Base64 (RFC 4648, section 5) solves this by substituting “-” for “+” and “_” for “/”, and typically omitting the “=” padding. The result is a string that can be placed directly in a URL query parameter, cookie value or filename without any percent-encoding. JWT tokens always use URL-safe Base64 for this reason.
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Decoding Base64 reverses the encoding process: it takes four Base64 characters and converts them back to three bytes of binary data. For text data, the bytes are then interpreted as UTF-8. The decoder must handle several common variations: line breaks inserted by MIME (every 76 characters) must be stripped before decoding; URL-safe characters “-” and “_” must be converted to “+” and “/”; missing padding “=” signs must be restored. A robust decoder — like this one — handles all these automatically so you can paste any Base64 variant without pre-processing it.
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Base64-encoded images are embedded in HTML and CSS as data URIs in the format data:[MIME type];base64,[encoded string]. A 1KB PNG icon becomes roughly 1.37KB as a Base64 string. For small images — icons, logos, inline SVGs — the tradeoff is worthwhile: the image loads with the page, requires no separate HTTP request, and is always available even if the CDN is unreachable. For large images the 33% overhead outweighs the benefit. Drop any image file onto the file drop zone in this tool to get the Base64 string; prefix it with the appropriate data URI header to embed it in your CSS or HTML.
Binary to Base64 converter
Any binary file — image, PDF, audio, video, archive — can be Base64-encoded. The encoding treats the file as a stream of raw bytes regardless of format. The FileReader API in modern browsers can read any file as an ArrayBuffer and the btoa function (or TextEncoder/TextDecoder chain) converts the binary data to Base64. This tool uses the FileReader API to read dropped files locally, never uploading them to a server. The output is a raw Base64 string (not a data URI) that you can use in any context that expects Base64-encoded binary data.
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MIME (Multipurpose Internet Mail Extensions, RFC 2045) defines how email messages encode attachments and non-ASCII characters. MIME Base64 has one important formatting requirement: lines must be no longer than 76 characters, separated by CRLF (carriage return + line feed). This prevents older email systems from truncating long lines and ensures compatibility with all SMTP implementations. Select “76 chars (MIME)” in the line wrap dropdown to produce MIME-compliant Base64 output suitable for use in email headers, MIME parts and legacy systems that require line-wrapped Base64.