Is this a cryptographically secure checksum?

No, this is a simple additive checksum meant for education and basic integrity spot-checks — it's easy to construct different strings with the same checksum, so don't use it for security purposes.

Why take the sum modulo 256?

Modulo 256 wraps the result into a single byte (0-255), which is how many simple legacy checksum schemes represent their result compactly.

ASCII Checksum Calculator

Calculate a simple additive checksum for a string by summing the ASCII (character code) value of every character, with an optional modulo-256 wraparound. Useful for basic data integrity checks and understanding how simple checksum algorithms work.

Inputs

Results

Raw ASCII Sum: 131
Checksum (mod 256): 131

Try an example

Formula

Checksum = Σ (ASCII code of each character), optionally mod 256

Learn How This Works

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