Verify Your Windows Update/KB File

Verify your Windows updates are safe and ready for install - in under a minute!

1

Windows Update Catalog Download

2

Select the file below

3

Paste Microsoft's hash

4

Click Verify - Done!

📘 Need help? Click "Guide" at the top for a quick tutorial and step-by-step instructions.

💾 Skip the website next time! Just right-click anywhere on this page and select "Save Page As..." (or press Ctrl+S).

Step 2: 📁 Select File

Drag and drop your Microsoft download here, or click to browse

Step 3: 📋 Paste Microsoft's Hash

⚙ Troubleshooting

Algorithm Override:

Auto-detect (Recommended) SHA-256 SHA-1

The tool automatically detects the hash algorithm based on length. Manual selection is only needed for troubleshooting.

Step-by-Step Guide

This short tutorial shows how to verify a Windows Update/KB file using the Windows Update Verifier. These steps can be done from any browser, operating system, and device. I've even tested this on my phone! Just make sure to delete the Windows Update file when you're done.

No installs, no scripts. Just this HTML text file in your browser.

⚠ Note: Images require an internet connection to view. The tool itself works 100% offline once loaded or if you save the HTML page.

STEP 1 Download the Update File from Windows

Visit the Microsoft Update Catalog.
(For this example, we're using Update Rollup 2 for Microsoft System Center 2012: Orchestrator Runbook Server, KB2702112.)
You'll see a page like this. Click Download.

A small popup window appears. Click the file link (purple highlight) to download the update file. Below, you'll see Microsoft's SHA1 and SHA256 hashes. You'll need these later.

STEP 2 Find and Copy the Microsoft Hashes

Locate the two hash values in the download window:

(SHA1: 4fE9xcwZeJQ9sD93v7bih24DIiE=) (SHA256: nAEw6UTrVlUGI6GptgfGl3iKJDmOE+2YTHuXbzwcViE=)

Tip: You can paste both hashes at once. The tool will automatically detect which algorithm each hash uses.

STEP 3 Using the Windows Update Verifier tool

Open the Update Verifier tool from online or directly from HTML.

Select your downloaded .cab file.

Paste Microsoft's hashes into the text box.

Click Step 4: ✓ Verify Hash.

Results:

✓ MATCH! The download file is an exact match to Microsoft's. It's safe and ready to install.

STEP 4 Force a Mismatch for Testing the Tool (Optional)

To test the tool's mismatch detection, just change a character in either or both hashes before clicking Verify.
(Leave the same file selected.)

For example, replace the current hashes with the following, in which exactly one character in each hash has been changed:

(SHA1: 4fE9xcwZeJQ9sD93v7bih44DIiE=)
(SHA256: nAEw6UTrVlUGI6GptgfGl3iKJDmOE+2YTHuXbfwcViE=)

You'll get a red "Not a Match" screen, with differences highlighted in the Technical Details section.

✗ NOT A MATCH! The file does not match Microsoft's published hash.

Done! 🎉

Congratulations! You've successfully verified a Microsoft update file using only your browser.

No installations, no command-line tools, and your file never leaves your device. Everything runs locally in your browser using the Web Crypto API.

Best Practice: Use this method to safely verify any Microsoft update or CAB/MSU/EXE file before installation.

About this Tool

TL;DR

This tool is an HTML file your browser displays, like opening a PDF. Your browser then uses its built-in calculator (Web Crypto API) to verify your file's hash.

That's it. Text File + Calculator. No coding, scripting, downloading, installing, or uploading involved. Everything runs locally on your device.

How It Works

When you open this tool, your browser simply displays an HTML file stored on your computer. Think of your browser as a universal file viewer. Just like it can show PDFs without Adobe or images without Photoshop, it displays this HTML file without needing any special software.

The "verification" part uses the Web Crypto API, which is built into every modern browser. This is essentially your computer's calculator doing math with your file's data. The calculation happens entirely within your browser window, which is called "client-side" processing. Your file never leaves your computer, and nothing gets saved or uploaded anywhere.

Think of it like using Windows Calculator to add numbers. You type 5 + 3, get 8, and nothing is sent online. Hash verification works the same way. Your browser reads your file, does the math, and shows you the result. All local, all offline, all safe.

Try It Yourself

Demo 1: Make a Simple HTML Web Page

Open Notepad.
Paste this text:

<!DOCTYPE html>
<html>
<head>
    <title>Hello World Page</title>
</head>
<body>
    <h1>Hello World!</h1>
    <p>This is my first HTML page.</p>
</body>
</html>

Save it as hello-world.html.
In the Save dialog, select "All Files," not .txt.
Double-click hello-world.html.

Takeaway: That's exactly how this hash verifier works. It's just an HTML file your browser displays. No internet, no installation, no magic.

Demo 2: Using a Web Browser as a Display Window

Find any PDF file on your computer.
Right-click it.
Select "Open With" and choose a web browser.
Is the PDF now online or still on your computer?
Hint: Look at the address bar. It should say something like file:///C:/Users/YourName/Documents/example.pdf.

Takeaway: Your browser can display files from your computer without putting them online. It's just showing the file, not sending or hosting it.

Demo 3: Download and Use This Tool Offline

Let's prove this tool works completely offline by downloading it from the internet first, then using it without any connection.

In Chrome, navigate to https://kbcheck.toolboxtinker.com/
Right-click anywhere on the page.
Select Save Page As....
Name the file local_index.html.
Make sure the filetype is html or htm (not txt/text).

Now test that it works offline:

Turn off your internet and/or enable Airplane Mode.
Confirm no internet by trying to Google something (it should fail).
Open File Explorer and find local_index.html where you saved it.
Double-click local_index.html to open it in your browser.

The tool opened in your browser, but it's not online. Look at the URL. It should show file:///C:/Users/YourName/.../local_index.html. This is just like when we opened a PDF in the browser.

Now try using the tool as you normally would. Select a file, paste hashes, verify. It still works perfectly!

Takeaway: You've just proven the tool requires no internet connection. Everything runs locally on your computer.

Demo 4: Math Without a Calculator App

Your computer already knows how to do math natively. Here's how to prove it.

PowerShell:

5 + 3

Command Prompt (CMD):

set /a 5+3

Takeaway: That's exactly how your computer does math internally. The browser simply asks it to do the same thing (just with file data instead of numbers) and shows the results.

Summary

Your browser isn't the internet. It's just a tool that can display files and has its own built-in calculator (among other functions).

The Windows Update Verifier uses those built-in abilities:

Display an HTML page (just formatted text, viewed in browser like a PDF)
Use the browser's built-in calculator (Web Crypto API) to do math
Display the result right on the screen

Everything stays local, safe, and offline.

Frequently Asked Questions

Does this tool need to be installed?

No. It's just an HTML file, the same kind of file every webpage uses. When you open it, your web browser displays it for you, just like a normal webpage. If you've got the HTML file saved locally, you can use it directly.

There's nothing to download, install, set-up, nor scripts to run.

Does it need the internet?

If you open the tool from https://kbcheck.toolboxtinker.com, you'll need internet to load it. However, once you've got the page loaded, the tool then works entirely offline. The browser doesn't contact any website or send your file anywhere. Everything happens locally.
You can also right-click and save this page for immediate offline use.

Check out Demo 3 under "Try It Yourself" on the "About" page to test this yourself.

What does the browser actually do?

The browser is just a window that displays the tool (the HTML file). Inside that window, it uses your computer's built-in "calculator" (the Web Crypto API) to do some simple math that verifies your file's authenticity. Nothing gets uploaded, saved, or modified.

Why Verifying Files Matters

The Simple Answer

You're making sure the file you downloaded is exactly what Microsoft published, byte-for-byte.

Even a single byte difference means the file is corrupted or incomplete, and installing it could brick your system. Hash verification catches these problems before they cause damage.

What Can Go Wrong?

File corruption from network and system issues is more common than you think - especially with legacy systems, slow networks, and large files:

Network issues: Slow connections, momentary drops, or bandwidth spikes can corrupt files during download
System lag: Older hardware under load can cause disk write errors
Storage problems: Failing drives or bad USB sectors introduce invisible single-byte errors
Wrong file version: Accidentally downloading the wrong update build

Even a single corrupted byte can brick your system. Hash verification catches these problems before installation, preventing crashes, boot failures, and costly downtime.

Real-World Example

You're installing a 500MB update on a critical production system over a slow, congested network. The download takes 20 minutes, with occasional connection drops.

Without verification: If even one byte got corrupted during download or USB transfer, installing it could brick the system. Friday afternoon emergency recovery scenario.

With verification (30 seconds): If the hash matches, you install with confidence. If it doesn't match, you download a clean copy first. Either way, you avoid bricking a critical system.

How Hash Verification Works (Simple Version)

When Microsoft creates a Windows update, they run it through a mathematical formula that creates a unique "fingerprint" (the hash). This fingerprint is published on their official update catalog.

When you verify the file:

You run the same mathematical formula on your downloaded file
You compare your result to Microsoft's published fingerprint
If they match exactly, the file is identical to what Microsoft created
If they don't match, even by one character, something is wrong

This mathematical formula is designed so that even the tiniest change to the file (changing one bit out of billions) will produce a completely different hash. It's virtually impossible for two different files to have the same hash.

Bottom Line

Hash verification is insurance that takes 30 seconds.

You get mathematical certainty that your file is exactly what Microsoft published. No corruption, no wrong version, no bricked systems. On legacy systems and slow networks, file corruption is common - this catches it before installation.

You're not clicking "trust me" - you're mathematically proving the file is correct.