Microsoft Compiled HTML Help File (.chi)
.chi file signature | application/octet-stream
Microsoft Compiled HTML Help is a proprietary help file format developed and maintained by Microsoft for Windows-based documentation systems. It stores compressed HTML pages, images, and navigation data for application help manuals, reference materials, and software assistance. The format is now largely legacy, and compiled help files have historically been associated with security concerns because they may contain active content, so files from untrusted sources should be opened cautiously.
Magic Bytes
Offset 0
49 54 53 46
Sources: Gary Kessler
Extension
.chi
MIME Type
application/octet-stream
Byte Offset
0
Risk Level
Safe
Validation Code
How to validate .chi files in Python
def is_chi(file_path: str) -> bool:
"""Check if file is a valid CHI by magic bytes."""
signature = bytes([0x49, 0x54, 0x53, 0x46])
with open(file_path, "rb") as f:
return f.read(4) == signatureHow to validate .chi files in Node.js
function isCHI(buffer: Buffer): boolean {
const signature = Buffer.from([0x49, 0x54, 0x53, 0x46]);
return buffer.subarray(0, 4).equals(signature);
}How to validate .chi files in Go
func IsCHI(data []byte) bool {
signature := []byte{0x49, 0x54, 0x53, 0x46}
if len(data) < 4 {
return false
}
return bytes.Equal(data[:4], signature)
}API Endpoint
/api/v1/chi
curl https://filesignature.org/api/v1/chi
See the full API documentation for all endpoints and parameters.
Related Formats
Frequently Asked Questions
What is a .chi file?
A .chi file is a Microsoft Compiled HTML Help File file. Microsoft Compiled HTML Help is a proprietary help file format developed and maintained by Microsoft for Windows-based documentation systems. It stores compressed HTML pages, images, and navigation data for application help manuals, reference materials, and software assistance. The format is now largely legacy, and compiled help files have historically been associated with security concerns because they may contain active content, so files from untrusted sources should be opened cautiously.
What are the magic bytes for .chi files?
The magic bytes for Microsoft Compiled HTML Help File files are 49 54 53 46 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.
How do I validate a .chi file?
To validate a .chi file, read the first bytes of the file and compare them against the known magic bytes (49 54 53 46) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .chi files?
There is no officially registered MIME type for .chi files. Systems typically use application/octet-stream as a generic fallback when handling this format.
Is it safe to open .chi files?
Microsoft Compiled HTML Help File (.chi) files are generally safe to open. They are classified as low risk because they primarily contain data rather than executable code. However, always ensure files come from a trusted source.