How to calculate MD5/SHA1/SHA256 checksums of a file without an external tool

Checksum is the easiest way to check if the content of a file is as it was expected to be or was changed/broken after a file transfer or an internet download.

A lot of websites (like CoolSoft) show the expected MD5/SHA1/SHA256 checksums beside each download link, so users can check "download health" after it completes.

After downloading a file you must calculate its checksum and compare it with the one reported beside the file.
If they are the same (you could also check only the first/last 8 chars) then you can be sure that the downloaded file is not corrupted.

There's a lot of free utilities available to calculate the checksum of a file, and one of them is already bundled in your Windows installation.
Below you'll find my suggestions.

Check with 7-zip

7-Zip is, IMHO, the best free & open source compression utility available on Windows; it can manage the well known .zip and .rar archives, but .7z file format is far better under many aspects.

It also has a great additional feature that allows user to calculate checksum of one or more files, straight from Windows Explorer.
Once installed, right click on a file then select the 7-Zip context menu and finally the CRC SHA submenu.
Select the checksum you'd like to calculate (or * to calculate them all) and a window is shown with the result… easy and clean 😉.

Check with certutil

certutil tool is (should be) already bundled in your Windows installation.

1. open Windows Explorer (Win+E) and go to the folder containing the downloaded file
2. while pressing the SHIFT key right click on an empty space into the folder
3. now choose "Open Powershell window here..." or "Open command prompt here"
4. a command prompt will open into the selected folder
5. now finally run certutil and make it calculate the required checksum (replace filename.exe with the filename you're going to check):

PS C:\testFolder> certutil -hashfile filename.exe MD5
MD5 hash of filename.exe:
2ffefb74864d962ef9fabde17031a4e7

PS C:\testFolder> certutil -hashfile filename.exe SHA1
SHA1 hash of filename.exe:
ade2405a022628835feac342c642a9113f630271

PS C:\testFolder> certutil -hashfile filename.exe SHA256
SHA256 hash of filename.exe:
4cc28a5be8dc7425a4c4fd23a75ca392f18be35d70232e777dce6d9f3b4d79ac

Supported checksums are: MD2, MD4, MD5, SHA1, SHA256, SHA384 and SHA512.