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Document format

HTM converter

.htm is the same HyperText Markup Language as .html, trimmed to three letters. The shorter extension exists because MS-DOS and Windows 3.x filesystems permitted only 8.3 filenames — eight characters, a dot, and a three-character extension — so early Windows web tools had no choice but to write INDEX.HTM.

Private for supported formats — processed in your browser

Convert supported files

Runs on your device

Drop HTM files here

Batch files can each use a different output. Nothing uploads for local conversions.

Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.

Where HTM comes from

When the web reached PCs in the early 1990s, the FAT filesystem's 8.3 naming limit collided with Unix's four-letter .html convention, and Microsoft tooling — including early IIS and FrontPage — settled on .htm instead. Long filenames arrived with Windows 95, yet the three-letter habit survives in legacy sites and IIS defaults to this day.

How HTM works

  • Byte-for-byte the same format as .html; only the filename differs.
  • Web servers map both extensions to the text/html MIME type, so browsers make no distinction.
  • IIS still lists Default.htm among its default documents, a living trace of the DOS constraint.
  • Renaming between .htm and .html changes nothing about the content — inbound links to the old name are the only thing that breaks.

When to use HTM

  • Maintaining legacy websites whose published URLs end in .htm.
  • IIS-hosted environments relying on Default.htm conventions.
  • Toolchains and embedded systems that still emit 8.3-style filenames.

Strengths and limitations

Strengths

  • Identical rendering support to .html in every browser.
  • Keeps decades-old bookmarks and inbound links working.
  • Interchangeable with .html by a simple rename, no conversion needed.

Limitations

  • Two extensions for one format invite duplicate-URL and SEO mistakes.
  • Some modern build tooling assumes .html and needs configuration to accept the short form.

Compatibility

Support is indistinguishable from .html: all browsers, editors, and servers accept it, and servers deliver it with the same MIME type. The choice between the two extensions today is purely a matter of convention and link preservation.

Convert HTM to another format