Split a large file into parts, or join them again

A file report.pdf split into three parts gives report.pdf.001, report.pdf.002 and report.pdf.003, the same scheme as HJSplit and 7-Zip split volumes; the number always has three digits, from 001 up to 999. Joining is plain concatenation in number order: 7-Zip opens the .001 file. On macOS or Linux run cat report.pdf.[0-9][0-9][0-9] > report.pdf: the three-digit pattern takes every part from .001 to .999 in order and leaves out the .sha256 file (a shorter pattern such as report.pdf.0* would stop at .099). On Windows run copy /b report.pdf.001 + report.pdf.002 + report.pdf.003 report.pdf, naming every part in order. Afterwards check the result with sha256sum -c report.pdf.sha256 (shasum -a 256 -c on macOS), or join the parts here to have it verified.

When splitting, the tool writes report.pdf.sha256 with the SHA-256 checksum of the original file in the sha256sum format. When joining, add that file to the selection: the joined bytes are hashed on your device and compared, and a mismatch is reported instead of a download. Without the checksum file the parts are joined but not verified.

The tool checks that the numbers run from 001 without gaps and that all parts share the same base name before joining, and tells you which part is missing. One part chosen on its own, such as report.pdf.003, is recognised as a part: the tool switches to Join and asks for the other parts, instead of offering to split it.

Splitting does not copy the file: each part is a slice of the file you chose, and a file above 256 MB is checked in 4 MB pieces. A join above 256 MB keeps the parts as they are and checks them piece by piece; a smaller join is put together in memory. At most 999 parts are produced; choose a larger part size for very large files. Browsers download parts one by one, so each part appears as its own download link. Sizes count as 7-Zip counts them: a KB is 1,024 bytes, an MB 1,048,576 and a GB 1,073,741,824.

No. The page loads a small script into your browser and every operation runs on your device. You can check this yourself in the browser's network panel: after the page has loaded there are no upload requests. Closing the tab discards the file.

No. These basic tools are free and store nothing on our servers. The only limits are the tool's own: at most 999 parts per split. Within them, the practical limit is your device's memory.

Nothing you open or type. While the tab is open, the tool pages keep a short list of the steps taken in it, in the tab's session storage: the step (page opened, started, succeeded, first success, used again or failed), the tool's name, the time, how many files were used and, for a failure, an error code; never a file name, the contents of a file or your text. It holds at most the latest 200 steps, and the browser deletes it when the tab closes. The page never sends it. Where a Report a problem button is shown, you can attach the last 20 steps to your report; nothing is attached unless you tick that box. In local storage the page keeps only choices you made: a Light or Dark theme until you choose System again, the language you picked with the EN / 中文 switch if it differs from your browser's language, and this tool in your recently used list if you switched that list on at the tools page.