Compute CRC and Fletcher checksums for data integrity checks
Checksums answer a different question from cryptographic hashes: not "could someone forge this" but "did these bytes survive the trip intact". This calculator covers the classic CRC and Fletcher algorithms used by ZIP, PNG, gzip and many binary formats.
- Algorithms
- CRC-32, Adler-32, Fletcher-16
- Output
- Hex and decimal
- Input
- UTF-8 bytes
How to use it
- Enter the data Type or paste the bytes you want to checksum. The text is converted to UTF-8 before the checksum is computed, which is what a command line tool would do.
- Pick the algorithm CRC-32 is the one used by ZIP and PNG. Adler-32 is the faster checksum used by zlib. Fletcher-16 is a lightweight variant found in many simple protocols.
- Compare the value A matching checksum confirms the data is byte-identical. A mismatch means corruption somewhere between the two ends.
Questions people ask
Which checksum does ZIP use?
CRC-32, the IEEE polynomial. Each member of a ZIP archive stores its own CRC-32 in the central directory, which is how unzip can verify a member after extraction.
Is CRC-32 good for security?
No. It detects accidental corruption, not tampering. Anyone can deliberately craft two different inputs with the same CRC-32 in seconds, so it must never be used for authentication or signature purposes.
What is the difference between Adler-32 and CRC-32?
Adler-32 is simpler and faster but detects fewer error patterns, and it is weak against reordering. CRC-32 is what you want for general file integrity.
How are the bytes encoded before hashing?
As UTF-8. If you are checksumming binary data, this text-based calculator is the wrong tool — use a file utility such as cksum or md5sum, which read the raw bytes.
Why does my checksum differ from the one on a command line?
Most often the encoding differs, or a trailing newline was added or removed when the text was copied. A newline is a byte, and one extra byte changes the checksum completely.
Can I checksum a file here?
Not as a file upload — this tool works on text, and the point of a checksum utility is to check bytes exactly. Use your platform tool for files: cksum on macOS and Linux, Get-FileHash on Windows.
Details that catch people out
A CRC is short, fast and detects accidental corruption, but it is trivial to forge: you can construct a collision in seconds. A cryptographic hash is designed so that producing a matching value is computationally infeasible. Choose a CRC for integrity against noise, a hash for integrity against an adversary.
Where this earns its keep
Verifying a transferred payload
A CRC attached to a data frame detects truncation and bit flips in transit, which is exactly what a transport protocol needs and what a cryptographic hash does not do efficiently.
Debugging a corrupt archive
When a ZIP file refuses to open, comparing the CRC of each member against the value in the central directory tells you whether the archive itself is damaged or the data was altered.
Implementing a binary format
If you are writing a parser for a format that includes a checksum field, the exact algorithm and byte order matter, and this gives you a reference value to test against.
Last reviewed 2026-09-28. Every tool on DevSnap runs entirely in your browser, so whatever you paste here never reaches a server.