ZIP Integrity Checker
Verify the CRC-32 of every entry in a .zip and flag any file that no longer matches.
What is Integrity Checker?
A verifier for ZIP archives. Every entry is checksummed and compared against the CRC-32 stored in the archive's central directory when the file was created.
How it works
The central directory supplies the expected CRC-32 for each entry. The entry is then decrypted if needed, inflated, and checksummed with the same CRC-32 algorithm, and any mismatch is reported with both values. A plain-text report is available for the record.
- Add your files. Drop files (or a whole folder) onto the drop zone. Browsers hand the contents straight to the page, so nothing is uploaded.
- Choose the options. Pick the format, compression, naming rule or split size. Any change re-computes the preview immediately.
- Download the result. Run the tool and grab the archive, the extracted files or the report. Multi-file results come back as a single .zip.
Examples
A 240 MB photo folder → a 52 MB .zip
JPEGs are already compressed, so the archive only saves 10–15% — but adding the folder structure and a manifest makes the upload verifiable.
A download cut off at 1.4 GB
The File Splitter cuts it into 500 MB chunks that fit the host's limit, and the File Joiner reassembles them, refusing any set with a missing part.
A release bundle with checksums
The Manifest Generator writes sha256sum-style lines next to the files, so the recipient can prove the download arrived intact.
Common mistakes
Expecting ZIP to shrink photos, video or audio
Those formats are already compressed; deflate typically saves single digits on them. ZIP is at its best on text, JSON, CSV, logs and source code.
Treating ZipCrypto as real encryption
Traditional ZIP encryption is legacy and breakable. It stops casual snooping only — for secrets, encrypt the contents with AES-256 first.
Renaming extensions to convert a file
Changing .png to .jpg does not change the bytes inside. Some programs will refuse the file, or display garbage. Use a real converter when the format must change.
Splitting without keeping the suffixes
The parts carry .001, .002 … suffixes on purpose: the joiner orders them by number and fails loudly when one is missing, instead of producing a corrupt file.
Frequently asked questions
What does a CRC mismatch actually mean?
The bytes on disk are not the bytes that were archived — a truncated download, a bad copy, a failing disk or a corrupted transfer. Re-download the archive from the source rather than trusting the damaged copy.
Does CRC-32 prove a file is safe?
No. It detects accidental corruption, not tampering — an attacker can change a file and recompute the checksum. For provenance, verify a SHA-256 manifest from a trusted source, or a signature.
Why do encrypted entries need a password?
The data must be decrypted before it can be checksummed. A wrong password is reported separately from a CRC failure, so you can tell the two apart.