or click to choose. Compress several at once.
Add a CHM file to compress it. You can also look inside and pull out its pages as regular HTML.
Processed entirely in your browser. Your files are never uploaded.
This CHM compressor packs Windows Compiled HTML Help files into a .zip or .gz for sending and storage, checks that the copy is perfect, and tells you honestly how much it saved. It also opens the CHM so you can see what’s inside, and can pull every page out as plain HTML files that open in any browser on Mac, Linux, phones and tablets. Nothing is uploaded.
How to compress a CHM file
- Drop one or more
.chmfiles onto the left box, or click it to choose them. - Pick .zip (opens on every computer) or .gz, and a compression level. Compression starts right away.
- With Verify on, the tool unpacks the result again and confirms it matches the original byte for byte.
- Download the compressed file, or open Inside the file to browse the contents and download the pages as HTML.
Why CHM files barely shrink
A CHM is already a compressed archive. When the help file is built, Microsoft’s HTML Help compiler packs every page, image and stylesheet with LZX compression, which usually beats the compression ZIP uses. So zipping a CHM typically saves only 0–10%. The Inside the file tab shows how big the contents are unpacked, so you can see how much compression is already built in.
| What you want | Best option |
|---|---|
| Send a CHM by email or chat that blocks .chm files | Compress to .zip. Many services block .chm attachments but allow .zip. |
| Archive help files with checksums | Compress with Verify on, and keep the SHA-256 shown in the results. |
| Read a CHM on a Mac, phone or Chromebook | Use Download pages to get the HTML, then open the start page in a browser. |
| Make the CHM itself smaller | Rebuild it from the source project with smaller images. The compiled file can’t be squeezed much further. |
Pulling the pages out of a CHM
The Inside the file tab lists the help file’s title, language, start page and every file it contains. Click Download pages (.zip) to unpack the HTML pages, images, stylesheets and table of contents into a normal ZIP. The ZIP includes a START-HERE.html file that opens the help file’s home page, so you can read it in any browser. Links between pages keep working because the folder structure is kept as-is.
CHM opens blank or says “navigation to the webpage was canceled”
That’s Windows blocking a help file that came from the internet, not a broken file. Right-click the .chm, choose Properties, tick Unblock and click OK. Also make sure the file isn’t in a folder with a # in its name, and that it’s on a local drive rather than a network share. Compressing or unzipping the file doesn’t cause this.
Is it private?
Yes. Compression, verification and page extraction all happen in your browser. The files never leave your computer, and the help file’s pages and scripts are never opened or run.
Frequently asked questions
Will the CHM still work after unzipping?
Yes. The ZIP holds an exact copy of the original file, and with Verify on the tool proves it by unpacking the result and comparing it to the original.
Should I choose .zip or .gz?
Choose .zip unless you know you need .gz. Windows and macOS open .zip files with a double-click. .gz is common on Linux and slightly smaller, but Windows needs a tool like 7-Zip for it.
Why is my compressed file only a few percent smaller?
Because the CHM was already compressed when it was built. That’s normal. The results show the built-in compression ratio so you can see why.
Can I convert a CHM to PDF?
Not directly with this tool. Download the pages as HTML, open the start page in your browser and print the pages you need to PDF.
What are the files starting with # and $ inside?
Those are the CHM’s internal indexes, like the search index and the lists used for the table of contents. They’re listed for completeness but left out of the page download, since browsers don’t use them.