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File Split & Join

Cut a file to a size you choose (around 18 MB suits a 25 MB mail limit), save it as name.ext.001, .002 … and put it back together on the same page. Multi-GB files are read in small pieces on your device, so memory stays flat. Missing or mixed-in parts are reported before joining, and a SHA-256 record confirms the result.

On-device・No upload

Your files and input are processed only inside your browser on this device and are never uploaded to our servers.

Drop the file to split (one file, any size)

or

Files are not uploaded — everything is processed on this deviceAccepts: Any formatPaste (Ctrl+V) also works

How to use

  1. In “Split”, drop the file or click “Choose file” (one at a time; there is no size limit).

  2. Set the size of each part (units are explicit: MB vs MiB) or the number of parts. Presets for email limits, such as 18 MB, are provided.

  3. Choose how to save: download one by one, save straight into a folder (desktop Chrome / Edge), or bundle everything into one ZIP. Keep “also create a .sha256” on to enable verification.

  4. The recipient opens “Join” and selects every part (and the .sha256), or drops the folder or ZIP. Parts are sorted by number automatically, and gaps, duplicates, wrong sizes and parts from another file are flagged.

  5. Press “Join and check” to rebuild the file. With a .sha256, a match or mismatch is shown — including which part number is damaged.

What it does

Flat memory, even for multi-GB files

The file is read 8 MiB at a time with Blob.slice and cut into parts while the hashes are updated. Neither splitting nor joining ever loads the whole file into memory. Progress, speed and time left are shown, and you can cancel.

Numbering compatible with 7-Zip and HJSplit

Names are name.ext.001, .002 … and grow to .1000 after 999, the same rule 7-Zip uses. Sets made by other tools can be joined here, and sets made here can be joined by 7-Zip, copy /b or cat.

Problems found before joining

After sorting by number, it reports gaps, duplicate numbers, a middle part with the wrong size and parts from a different file, showing exactly which are at fault. With a .sha256 it also checks the expected count and sizes.

SHA-256 records pinpoint a damaged part

The SHA-256 of the original and of every part are written to a sha256sum-compatible .sha256. If the joined file does not match, the part numbers that differ from the record are listed, so only that part needs to be sent again.

Choose where to save; ZIP64 supported

Desktop Chrome / Edge write straight into a folder or file with no size limit. Other browsers use per-part downloads or an uncompressed ZIP (ZIP64 records are added automatically above 4 GiB). A ZIP can be fed straight back into Join.

Use cases

  • Send a document or video that exceeds an email attachment limit (25 MB, for example) in several messages
  • Upload a large file to a service with an upload size cap by splitting it
  • Move a large file to a FAT32 USB drive, where one file can be 4 GB at most
  • Rebuild .001 .002 … files made by 7-Zip or HJSplit without installing anything
  • Confirm with SHA-256 that all received parts are present and undamaged

Supported formats

Files to split

Any format (bytes are cut as they are)One file at a time, no size limitUp to 9999 parts

Joinable

name.ext.001 sequences (this tool, 7-Zip, HJSplit …)A whole folder, or parts inside a ZIP.zip.001 → saved as ZIP / .7z.001 → saved as 7z.sha256 / SHA256SUMS checksum files

Saving

Individual downloadsSave to folder (desktop Chrome / Edge)Uncompressed ZIP (ZIP64 aware)

Capability matrix

FeatureSupportNotes
Split by part size or number of partsSupportedUnits MB / GB (1,000-based) and MiB / GiB (1,024-based). Up to 9999 parts
Join numbered parts (gap, duplicate, size and mix-up detection)SupportedSorted by number automatically. Joining is blocked while parts are missing or duplicated
Join .001 sets made by 7-Zip, HJSplit and othersSupportedPlain sequential splits only. .zip.001 is saved as a ZIP, .7z.001 as a 7z
SHA-256 verification (.sha256 or pasted value)SupportedIdentifying the damaged part works with a .sha256 made by this tool
Choosing the save location (write straight to folder / file)PartialOnly desktop Chrome / Edge (File System Access API). Firefox, Safari and phones save by download
Writing parts into an uncompressed ZIPPartialCapped at 8 GiB on desktop and 1 GiB on phones (a safety value set by this tool)
Joining parts stored in a ZIPPartialStored and Deflate only; no passwords. Deflated parts are unlimited when you choose the save location in a desktop browser, but capped at 1 GiB for download saves
Splitting several files at onceNot supportedOne file per run
Encryption, passwords or compressionNot supportedIt only cuts the bytes. Compress or encrypt first with another tool if needed
RAR .part1.rar / .r00, or ZIP / 7z native volumes (.z01)Not supportedOnly plain “.001” numbered sequences are supported
Resuming an interrupted run; offline usePartialNo resume (start again). Works without a connection once the page has been loaded

Limits & notes

  • One file can be cut into at most 9999 parts (a size that would exceed that is rejected). There is no file-size limit, but speed depends on the device and storage (roughly several hundred MB/s for reading plus hashing).
  • Where you cannot choose the save location (Firefox, Safari, phones), saving a joined file and building a ZIP are capped at 8 GiB on desktop and 1 GiB on phones and tablets. Splitting into individual downloads has no cap.
  • Safari on iPhone / iPad may ask for confirmation on each of several downloads and has little memory to spare. Prefer a ZIP when splitting there, and use a desktop browser for large files.
  • Up to 20,000 files can be added for joining; checksum files (.sha256) are read only up to 2 MB. Parts inside a ZIP joined without choosing a save location are limited to 1 GiB because of memory.
  • A .sha256 cannot protect against someone who rewrites the record itself. For important files, also pass the SHA-256 along through a separate channel.

Privacy & safety

Files are never uploaded. Your browser reads them directly to cut, join and hash them. File names, contents and hashes are not sent to or stored on any server. When saving to a folder, a new folder is created inside the place you choose and existing files are never overwritten.

FAQ

My mail limit is 25 MB — what part size should I use?
Around 18 MB. An email attachment grows by about 1.37× when it is Base64-encoded for sending, so a 25 MB limit fits roughly 18 MB of original data. Pick the “18 MB” preset. The unit selector makes the MB (1,000-based) versus MiB (1,024-based) difference explicit.
How does the recipient put the file back together?
The easiest way is to select or drop all the parts (and the .sha256) into “Join” on this page. With software: right-click the first part (.001) in 7-Zip and extract. On Windows, copy /b "name.001"+"name.002" "name" works; on Mac or Linux, cat name.0* > name.
What happens if one part is missing?
The Join view lists it by number as “Missing” and blocks joining until all parts are present. If a download was cut short, rows with a different size are warned about as well. With a .sha256, even a missing final part is noticed from the recorded count.
Can it join .7z.001 or .zip.001 made by 7-Zip?
Yes. Any “name.ext.001” sequence, including ones split with 7-Zip or HJSplit, is joined as is. The result is named “name.7z” or “name.zip”; extract it with the Archive tool. RAR .part1.rar and native ZIP .z01 volumes cannot be joined.
Will the browser freeze on multi-GB files?
The file is read 8 MiB at a time, so memory stays almost flat. Saving straight to a folder or file in desktop Chrome / Edge has no size limit either. In other browsers and on phones, building a ZIP or downloading the joined file is capped (8 GiB desktop, 1 GiB phones).
Is anything sent to a server?
No. The browser reads the files locally and nothing leaves your device. File names, contents and hashes are neither sent nor stored, and once loaded the tool also works offline.

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