Tools
Test whether a ZIP file is intact
Choose an archive and we read every single file in it, checking the checksum against what the archive itself states. Nothing is uploaded, and nothing is written to your disk.
Choose the archive you want to test
The file is handled in your own browser. It is not sent to any server, and it is not left behind anywhere afterwards.
How the test works
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We read the table of contents at the back of the archive. It states which files should be there, how large they are, and which checksum each of them should have.
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Then every file is unpacked in memory, and the checksum is recalculated. If it does not match what the table of contents promises, the file is damaged.
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You get a list of what is in order and what is not. None of this is written to the disk along the way.
What the test answers — and what it does not do
A passed test means the archive can be read, and that every file comes out exactly as it was put in. It is a check that the transfer and the storage went well.
It says nothing about whether the content is safe. We are not an antivirus program, and a file can be both intact and harmful at the same time. If you are unsure about the sender, this test does not help you.
Why archives get damaged
- The download was interrupted. That is by far the most common cause, and usually gives an archive that is missing its end.
- The file was sent through something that changed it on the way — some email systems and file services alter content they believe is text.
- The storage medium has faults. A memory stick or an old hard drive can change single bytes without saying so.
- The archive was split into several files, and you only have the first one. Then most of the content is missing.
Locked and unknown entries
If a file in the archive is password protected, we cannot check it without the password. It is listed as skipped, not as failed — a difference that matters when you judge the result.
The same goes for entries packed with a method we do not support. To open a locked archive, go to Open ZIP file, which asks you for the password.
Questions and answers
Are my files uploaded?
No. The whole test runs in your own browser, on your own machine. You can check it yourself: open the developer tools in your browser, go to the Network tab, and see that no request goes out while the test runs.
How large an archive can I test?
The test reads one file at a time and drops it from memory afterwards, so the size of the archive itself is rarely the problem. The limit is 20,000 files in one archive. Archives over 4 GB are handled through the ZIP64 extension.
The test says the archive has errors. Can it be saved?
We do not repair archives, and we are not going to. What you can try is downloading the file again from the source — if the cause was an interrupted download, that solves it by itself. If the files still matter, there are dedicated repair programs, but the result is rarely complete.
What does it mean that a file was skipped?
That we could not check it — usually because it is password protected, or packed with a method we do not read. That is not the same as it being damaged. The rest of the archive may be perfectly fine.
Can I test RAR or 7z files?
No, the tool reads ZIP. If you have an archive in another format, use the program that belongs to it — 7-Zip has its own test function that does the same for its formats.