OpenAnyFile
Works
Viewing, inspecting and verifying. You get a byte-level hex and ASCII dump alongside the detected signature, exact size and type analysis. File details, exact byte size and the detected signature are always shown.
How to open a .chm file
Opening a CHM file usually means tracking down special software. It does not have to. Here is what the format really is, and a browser-based way to read one right now.
What is a .chm file?
Compiled HTML Help is a binary & system format developed by Microsoft, first appearing in 1997. It is normally produced by Windows help authoring, older ebooks.
An ITSS-compressed bundle of HTML pages, images and a search index. Windows blocks CHM files opened from a network location, which is why a downloaded one so often shows blank white pages.
| Full name | Compiled HTML Help |
|---|---|
| File category | Binary & system |
| MIME type | application/vnd.ms-htmlhelp |
| Magic bytes (file signature) | 49 54 53 46 (ITSF) |
| Developer | Microsoft |
| Introduced | 1997 |
| Usually created by | Windows help authoring, older ebooks |
| OpenAnyFile engine | universal hex inspector |
| Opens without upload | Yes — parsed locally in your browser |
Open a .chm file in your browser
OpenAnyFile routes .chm to its universal hex inspector, which inspects a byte-level hex and ASCII dump alongside the detected signature, exact size and type analysis.
- Open the OpenAnyFile opener in this browser — nothing to download or sign up for.
- Drag your .chm file onto the drop zone, click to browse for it, or paste it with Ctrl+V.
- The extension is detected and the file is handed to the universal hex inspector.
- Your CHM opens on its own viewer page: a byte-level hex and ASCII dump alongside the detected signature, exact size and type analysis.
- Use fullscreen for a closer look, or download the file back out unchanged. No account, no upload, no watermark, no file-size gate.
What you can and cannot do with it here
Does not work
Full-fidelity rendering. This extension has no standard structure, so you get a byte-level inspection rather than a rendered view.
Why your {ext} file is never uploaded
Most online viewers work by sending your file to their server, processing it there, and leaving a copy behind on infrastructure you do not control. OpenAnyFile does not. Your .chm file is read through the browser's local File API and decoded by JavaScript and WebAssembly running on your own machine. There is no upload step and no server-side copy — open your browser's network tab while you do it and watch: the file never appears.
Frequently asked questions about CHM files
Can I open a .chm file without installing special software?
Yes. OpenAnyFile's universal hex inspector runs in your browser, so you can read a CHM file with nothing installed. You get a byte-level hex and ASCII dump alongside the detected signature, exact size and type analysis. It will not replace the original application for editing, but it answers 'what is in this file' in seconds.
How can I check a file really is a CHM file?
Look at the first bytes rather than the extension. A genuine CHM begins with 49 54 53 46 (ITSF). Opening the file in OpenAnyFile shows that signature in the file-details panel, so a file renamed to .chm by mistake is easy to spot.
Is it safe to open a CHM file online?
With OpenAnyFile, yes, because nothing is uploaded. The file is read locally through your browser's File API and never leaves your device, so there is no server copy to leak, log or retain. That matters most for the kind of file people are least willing to hand to a random converter site.
What is a .chm file, exactly?
Compiled HTML Help — an application/vnd.ms-htmlhelp format created by Microsoft since 1997. An ITSS-compressed bundle of HTML pages, images and a search index. Windows blocks CHM files opened from a network location, which is why a downloaded one so often shows blank white pages.
Does the same viewer handle formats related to CHM?
Yes — the same engine also opens .dll, .doc, .exe, so you can compare related files without switching tools.
Related formats
These open with the same engine, so if you have one of these sitting next to your .chm file, it will open too: