About CRC8 Checksum
CRC8 Checksum computes the eight-bit cyclic redundancy check for a piece of text and prints it as two hexadecimal digits. Type or paste a value and the page returns the check value for it, recalculated on every keystroke.
The implementation is the classic bit-by-bit form: the text is converted to UTF-8 bytes, each byte is exclusive-ORed into an accumulator, and eight shifts are applied with the polynomial folded in whenever the top bit is set. That is the same procedure the CRC-8 table is normally generated from, written out longhand rather than read from a table.
The parameters are the common concatenated one - polynomial 0x07, starting value zero, no reflection of the bits and no final exclusive-OR. That combination is what a spreadsheet or a library will call CRC-8/SMBUS, and it is the one you want when you are checking a short identifier or a sensor reading against a value a device reports.
If the device or format you are working with specifies a different set of those four values, the checksum it produces will differ from the one shown here even though both are called CRC-8 - see the notes below for which parameters to compare first.
How to use CRC8 Checksum
- 1 Paste or type the text you want a checksum for.
- 2 Read the two-character hexadecimal result, which updates as you type.
- 3 Compare it against the value reported by the device or program you are matching.
- 4 Check the parameters listed below if the two values do not agree.
Frequently asked questions
Can I use it to verify a downloaded file?
Not safely. An eight-bit check has only two hundred and fifty-six possible values, so roughly one in every two hundred and fifty-six random corruptions will still produce a matching checksum. It is designed to catch a flipped bit in a short frame, not to prove that a whole file arrived intact - a longer digest is the right tool for that.
Why does my device report a different value?
Almost certainly because it uses a different CRC-8 variant. The polynomial, the starting value, whether the input and output bits are reflected and the final exclusive-OR are all parameters, and changing any one of them changes every result. This page uses 0x07 with a zero start and no reflection or final XOR, which is the family usually labelled CRC-8/SMBUS or CRC-8/ATM.
Does it work on binary files?
It works on text. The panel accepts characters, not raw bytes, so there is no way to feed it a file directly or to enter a hexadecimal byte sequence - which makes it awkward to use as a debugging reference when you are comparing against a protocol that works in bytes.
Is the checksum a security feature?
No. A CRC is an error-detecting code and is trivial to compute for any input, so it offers no protection against deliberate tampering - an attacker who alters the data can simply recalculate it. If you need to detect a change you did not make, a keyed hash is what you want.
Free, online, and private
Free to use
CRC8 Checksum is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How CRC8 Checksum behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Input | a text panel; the sample value is "Hello world" |
| Encoding | the text is encoded to UTF-8 bytes first, so non-ASCII characters contribute more than one byte |
| Polynomial | 0x07 - the CRC-8/ATM polynomial, applied bit by bit rather than through a lookup table |
| Output shape | exactly two lowercase hexadecimal digits, zero-padded, from 00 to ff |
| Initial value | zero, with no final XOR and no reflection of input or output bits |
| Comparison | computed over the whole input each time the text changes, with no incremental update |
Compiled from the implementation of this tool and checked against it by itoolnet.
What CRC8 Checksum does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- It is not a general-purpose file checksum. CRC8 is an eight-bit value, which means one in every two hundred and fifty-six random alterations goes undetected - it is suited to catching a flipped bit in a short frame, not to proving that a download arrived intact. For that, a tool producing a longer digest is the right choice.
- One specific CRC-8 variant is implemented. The source uses polynomial 0x07 with a zero initial value and no final XOR or bit reflection - the parameter set usually called CRC-8/SMBUS or CRC-8/ATM. A device or library that specifies CRC-8 differently will not agree with the value shown here: CRC-8/MAXIM uses the same polynomial but reflects the input and output bits, and CRC-8/SAE-J1850 uses polynomial 0x1D with 0xFF as both the initial and the final XOR value.
- It reads text, not bytes. The editor takes typed or pasted characters, so there is no way to choose an arbitrary file, to select a hexadecimal input mode or to see the intermediate byte values that the checksum was taken over - which makes the tool hard to use as a reference when debugging a binary frame.
Tested and documented by itoolnet, the team that builds and maintains this site.