How do I open an .html file someone sent me?

On a desktop, double-click it — it opens in your default browser. If it opens blank or unstyled, the file is almost certainly missing the folder of assets that shipped with it, or it loads data over `fetch`, which browsers block on `file://` origins. On a phone, most mail apps won't open it at all. Publishing the file to a URL fixes all three cases at once.

Why does my HTML report open blank?

Two usual causes. The page loads its content as a module script or over `fetch`, and both are blocked from a `file://` origin by the browser's same-origin rules — nothing arrives, so nothing renders. Or the report was a folder and only `index.html` got sent, so every script and stylesheet reference points at files that aren't there.

How do I open an HTML file on an iPhone or Android?

You generally can't from the mail app — it previews the markup as text or offers a download that has nowhere to go. The reliable path is a URL: publish the file once and open the link, which renders in mobile Safari or Chrome like any other page.

Is it safe to open an HTML file from someone else?

Treat it like any attachment from that sender: HTML can carry scripts, and opening it locally runs them on your machine. Comma renders uploaded report HTML inside a sandboxed iframe with no same-origin access, so a script in a report can't read your session, cookies or storage — but that's a containment boundary, not a malware scanner. Don't publish files from senders you don't trust.

Is there a free way to turn an HTML file into a link?

Yes. Comma is free — drag the file (or the whole folder) in and you get a URL. You choose whether it's private, restricted to signed-in people, or open to anyone with the link.

Someone sent me an HTML file

It's a test report, a notebook export, a coverage summary or a dashboard someone generated. It's sitting in your downloads folder as report.html, and one of three things happens.

It opens, but it's blank or half-styled

The most common cause is that the file was never one file. nbconvert, genhtml, Playwright, Gatling, Sphinx and most of the tools that emit "an HTML report" actually emit a directory — index.html plus a sibling folder of CSS, JavaScript and JSON. Send only the .html and every one of those references resolves to nothing.

The second cause is the browser doing exactly what it should. A page opened from file:// has an opaque origin, so:

fetch() and XMLHttpRequest to a neighbouring file are blocked.
<script type="module"> won't load — module fetches follow CORS rules even locally.

Reports that load their results as JSON — Vitest's HTML reporter is the best-known example — are structurally unopenable this way. Their own docs tell you to run a local web server first.

It won't open at all on a phone

Mail clients on iOS and Android don't hand .html to the browser. You get a preview of the markup as plain text, or a download that lands somewhere you can't reach. There's no setting to fix this — the file needs to be at a URL.

It opens, and now you have a copy nobody else has

Even when it works, you've got a private artifact. Anyone who wants to look at the same numbers needs their own copy of the same file, and there is no way to say "the chart in section 3 is wrong" other than a screenshot with an arrow drawn on it.

The fix: give the file a URL

Drag the file — or the whole output folder, or a zip of it — into Comma:

index.html becomes the report body.
Every asset that came with it uploads alongside, and the relative references are rewritten to the uploaded copies. That's the step file:// can't do.
Scripts still run, inside a sandboxed iframe (allow-scripts, no allow-same-origin), so interactive reports stay interactive. See interactive HTML reports.

You get one URL. It opens on a laptop, on a phone, and for the person who doesn't have the file.

Who can see it

You pick, per report: private to you, your team, anyone signed in, or anyone with the link — with view, comment or edit rights for link holders. Full model in sharing & access control.

If the file came from outside your company and you're not sure what's in it, that decision matters more than usual — keep it private.

Then: comment instead of screenshot

Once it's a URL, feedback lands on the report itself. Select the number, leave a thread, and it stays anchored there across refreshes — see commenting on HTML.

Try it

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

Open your HTML file as a link →

Why the report lost its CSS — the styling case in detail
Email an HTML report · Share an HTML report
Stop screenshotting reports