Web
HyperText Markup Language is a web format commonly identified by .html, .htm. Use the listed signatures, MIME types, and structure notes to validate files beyond the extension.
3C 21 64 6F 63 74 79 70 65 <!doctypeSIGNATURE = bytes.fromhex("3c21646f6374797065")
OFFSET = 0
def is_html(path: str) -> bool:
with open(path, "rb") as f:
f.seek(OFFSET)
head = f.read(len(SIGNATURE))
return head == SIGNATUREconst SIGNATURE = [0x3c, 0x21, 0x64, 0x6f, 0x63, 0x74, 0x79, 0x70, 0x65];
const OFFSET = 0;
// bytes: a Uint8Array / Buffer holding the start of the file
export function isHtml(bytes) {
return SIGNATURE.every((byte, i) => bytes[OFFSET + i] === byte);
}package fileid
import "bytes"
var ishtmlSignature = []byte{0x3c, 0x21, 0x64, 0x6f, 0x63, 0x74, 0x79, 0x70, 0x65}
const ishtmlOffset = 0
func IsHtml(b []byte) bool {
end := ishtmlOffset + len(ishtmlSignature)
if len(b) < end {
return false
}
return bytes.Equal(b[ishtmlOffset:end], ishtmlSignature)
}const SIGNATURE: &[u8] = &[0x3c, 0x21, 0x64, 0x6f, 0x63, 0x74, 0x79, 0x70, 0x65];
const OFFSET: usize = 0;
fn is_html(bytes: &[u8]) -> bool {
bytes.get(OFFSET..OFFSET + SIGNATURE.len()) == Some(SIGNATURE)
}<?php
$signature = "\x3c\x21\x64\x6f\x63\x74\x79\x70\x65";
$offset = 0;
function is_html(string $bytes): bool {
global $signature, $offset;
return substr($bytes, $offset, strlen($signature)) === $signature;
}HyperText Markup Language is used for data exchange, imports, exports, parser testing, and validation workflows. Encoding, delimiters, versions, and container structure often change implementation behavior.
Untrusted input is not safe just because the format was detected. Account for parser exceptions, large files, unexpected encodings, and external references.
11 samples help test leading-byte detection, parser errors, upload limits, and download behavior.
Blue Sky HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
01-blue-sky.html3da0e54ffe7186921d2a037219ac03b1327b7577620940026310443163313586Flower Garden HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
02-flower-garden.html15223cb4d9e7c636861b0b5962036ead59ae9cddc063a0107e6023659047881fNavy Blue Sky HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
03-navy-blue-sky.html1744f855eb8576d2a4214de31d8e8d3bfdd10a74a859d59fa9beef5ac5ddba5bNature of the Sky HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
04-nature-sky.htmlb35642842f3519ebfeff7568034fbda82b01eaa8c9a01b09f7469d1c52fe348bSky Landscape HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
05-sky-landscape.htmld50339721c2fbfcc006ae76b198de485d019103bb70bd58fbfdef43f224fd6c8Starry Sky HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
06-starry-sky.html2a154d8e8e02c49a0483645749ee5d7078f143a9d66ceff82aeaf2c29eda3e08Blue Night Sky HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
07-blue-night-sky.htmlc2587341751a1e1e84dc0faf4faf3fac8a7b299635aeabc79ef38a7381f0d682Hibiscus Flower HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
08-hibiscus-flower.html6e078c2a2cff9855876aa42f18abdfb7113a8455794c9a44aabaa9af58ff6d2cArctic Sky HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
09-arctic-sky.html68603539b4b96df6f2131a7cc875e66f8b91cae9a7dba52202429c5efb52798cSunset Rays HTML is a HyperText Markup Language sample based on Wikimedia Commons. It can be used to test downloads, parsers, previews, and file type detection.
10-sunset-rays.html4637d3e25d6f3da6144f5d06afe94380772515c4c57080c1d77232a6335af455NASA Blue Marble HTML is a HyperText Markup Language sample based on NASA Image and Video Library. It can be used to test downloads, parsers, previews, and file type detection.
nasa-blue-marble-2012-east.htmlf7cee2a714ce3bf7b25a8dbeb549df87ffbe6b43accc032186bca5cc84e6fcc9HyperText Markup Language files begin with the byte signature 3C 21 64 6F 63 74 79 70 65 ("<!doctype"). Detect the format by reading these leading bytes rather than trusting the file extension alone.
The MIME type for HyperText Markup Language is text/html.
HyperText Markup Language files use the .html, .htm extension. The extension is a convention only and does not guarantee the file contents, so combine it with signature and structure checks.