Base64 to File Decoder Online — Download

Read the first few characters. JVBERi means PDF, iVBORw0KGgo is PNG, /9j/ is JPEG, and UEsDB is ZIP or an Office file such as docx or xlsx. If the data: prefix survived, the MIME type is written in it. Otherwise keep file.bin and rename the download once you can see what it contains.

No. Everything before the comma is discarded and the remainder is decoded, and a bare string with no prefix works just as well. What matters more is copying the tail of the string — truncated Base64 produces a file that looks right but ends mid-stream, and the viewer will refuse it.

Only the memory available to the tab. A few megabytes decode in about a second, but a hundred-megabyte string can freeze the browser: Base64 inflates data by roughly a third, and both the text and the assembled file sit in memory at the same time. Very large attachments are safer to decode with a local tool.

Nowhere outside the tab. The decoding uses the browser's own built-in function and the download is served from a temporary object created on this page. No request carrying your data is sent, so work attachments can be unpacked without handing them to a third-party service.

Usually one of three things: the string was copied incompletely, stray characters came along from the interface (quotes, or the ellipsis from a shortened console dump), or the extension does not match the real format. Recopy from the source, delete the ellipses and try again with the right extension.

Use the companion File to Base64 page: it takes a file through a picker and hands back the string. The two together close the loop — one turns a string into a file, the other turns a file into a string you can drop into JSON, CSS or an email body.