What is an MHTML file?

MHTML (MIME HTML, RFC 2557) is a web page archived as a single file: the HTML plus its stylesheets, images and scripts, each stored as a part of a MIME multipart/related message, the same structure an email uses for attachments. The extensions are .mht and .mhtml. Chrome and Edge produce it with Save as → 'Webpage, Single File'.

How do I open an .mht or .mhtml file?

Open it from disk in Chrome or Edge on a desktop — drag it onto a window or use Open with. Firefox does not open MHTML without an extension, Safari uses its own .webarchive format instead, and phones generally have no app that renders it.

Why won't an MHTML file open from a website?

Chromium-based browsers only render MHTML loaded from a local file; an MHTML served over HTTP or HTTPS is downloaded or refused rather than rendered, because a multipart archive can claim content from any URL inside it. So an .mht cannot be hosted and linked like a normal page.

What is the difference between MHTML and HTML?

An .html file is one document that references its resources by URL. An .mhtml file packs the document and those resources together as MIME parts. A self-contained HTML file — resources inlined as , and data: URIs — achieves the same 'one file' goal while staying ordinary HTML that every browser opens.

How do I convert MHTML to HTML?

Open the .mhtml in Chrome or Edge and use Save as → 'Webpage, Complete' to get an .html plus a folder of resources; then fold that folder into one file with an HTML inliner. Or publish the folder as a link so it opens anywhere.

MHTML

MHTML (MIME HTML) is a format for saving a web page and every resource it needs — stylesheets, images, scripts, fonts — as a single file, using the MIME multipart/related structure from email. It is defined in RFC 2557 (1999). Files end in .mht or .mhtml.

How it works

An MHTML file is literally an email-shaped message:

From: <Saved by Blink>
Subject: Test report
MIME-Version: 1.0
Content-Type: multipart/related; type="text/html"; boundary="----MultipartBoundary--abc"

------MultipartBoundary--abc
Content-Type: text/html
Content-Location: https://example.com/report/

<!DOCTYPE html><html>…<link rel="stylesheet" href="style.css">…

------MultipartBoundary--abc
Content-Type: text/css
Content-Location: https://example.com/report/style.css

body { font-family: system-ui }

Each part carries a Content-Location. When the browser renders the HTML part and meets style.css, it resolves the URL and serves the matching part from inside the archive instead of the network. Binary parts are base64-encoded, which costs about a third more bytes — the same tax as a data URI.

Who makes it

Chrome and Edge: Save as → Webpage, Single File (.mhtml).
Internet Explorer originated it as Web Archive, single file (.mht).
Microsoft Word and Excel: Single File Web Page (.mht) — one reason old intranet reports still arrive in this format.
Safari does not; its single-file format is .webarchive, a property list that only Safari reads.

Where it fails

MHTML solves "keep it as one file" and then works almost nowhere else:

Opened from	Result
Chrome / Edge, local file, desktop	Renders
Firefox	Not supported without an extension
Safari	Not supported
iPhone or Android	No app renders it
Served from a website over HTTPS	Downloaded or refused, not rendered
Email attachment preview	Shown as text, or as a download

The server case is deliberate. An archive can contain parts whose Content-Location claims any URL, so rendering a downloaded MHTML as if it were those pages would be a spoofing hole. Chromium only renders MHTML from a local file.

That rules it out as a way to share a report: you can't host it, phones can't open it, and half of desktop browsers can't either.

The portable alternative: self-contained HTML

The goal MHTML is chasing — one file, nothing missing — is reached more portably by a self-contained HTML file: CSS in <style>, scripts in <script>, images and fonts as data: URIs. It is still ordinary HTML, so every browser on every device opens it, and it can be served from a URL.

To convert an .mhtml:

Open it in Chrome or Edge on a desktop.
Save as → Webpage, Complete. You get page.html plus page_files/.
Drop both into the free HTML inliner to fold them into one .html.

Or skip the file entirely: drop the folder into Comma and send a link that opens on any browser, phone included.

Try it

Comma is free — unlimited reports, unlimited commenters, unlimited revision history.

Turn a report into a link →

Self-contained HTML · Data URI
HTML inliner — fold a report folder into one file
Open an HTML file on Android · on iPhone
Outlook blocked an HTML attachment