Source: https://mactoolbox.app/glossary/checksum

# What is a checksum?

By Nikhil Barik · Published November 3, 2026

## Quick answer

A checksum, or hash, is a short string calculated from a file's contents. If even one byte changes, the checksum changes, so it can confirm a download is complete and unaltered.

## What it is

Common algorithms are MD5, SHA-1, SHA-256 and SHA-512. Developers publish the expected checksum next to a download.

## Why it matters on a Mac

Comparing the published value with your own tells you whether the file arrived intact. MD5 and SHA-1 are fine for catching corruption but not for security. Use SHA-256 or longer when security matters.

## How to check it on macOS

In Terminal, run shasum -a 256 /path/to/file. Compare the output with the published value.

## How Toolbox handles it

Hash Generator computes MD5, SHA-1, SHA-256, SHA-384 and SHA-512 of text or files. Paste the expected checksum into Compare and it tells you which algorithm matches, or that it does not match. Find Duplicates also uses a SHA-256 of the whole file to confirm true duplicates.

## Frequently asked questions

**Is a checksum the same as encryption?**

No. A hash cannot be reversed to get the file back.

**What if the checksum does not match?**

Download the file again. If it still differs, do not trust it.

**Can I hash large files?**

Yes. Hash Generator reads files in chunks.

## Tools mentioned

- [**Hash Generator**: MD5, SHA-1 and SHA-2 checksums of text or files of any size, and check them against an expected hash.](https://mactoolbox.app/hash-generator-mac)
- [**Find Duplicates**: Find identical files across folders and move the extras to the Trash.](https://mactoolbox.app/find-duplicate-files-mac)

## Keep reading

- [Hash Generator](https://mactoolbox.app/hash-generator-mac)
- [Find Duplicates](https://mactoolbox.app/find-duplicate-files-mac)
- [Gatekeeper](https://mactoolbox.app/glossary/gatekeeper)