HTML file mode

Route: Spread → File tab

File mode is the escape hatch when URL mode can't reach your page — auth walls, SPA hydration, intranet hosts.

How it works

1. Toggle to the File mode at the top of the Spread page.
2. Click the file picker; choose a .html or .htm file from disk.
3. Tostada reads the file text-only — no upload, no network round-trip.
4. Click Spread to run the same pipeline as URL mode, applied to the file's HTML.
5. Drag the slider to compare.

Getting the HTML

Several options depending on the source:

• Browser "Save As" — File → Save Page As → "Webpage, Complete." Use the saved .html file. Assets (images, CSS) won't be inlined; the spread preview shows broken images, which is fine for evaluating the design but not for sharing the output.
• curl — curl https://example.com > page.html for any page that can be fetched server-side.
• Pre-render an SPA — many SPA toolchains have a prerender or static-build mode that outputs HTML files. Run that, then drop the result in.
• Hand-craft — paste any HTML into a file. Useful for previewing how your library handles a specific component or pattern.

Size and format limits

• Plain text HTML only (text/html MIME).
• No size limit beyond what the browser allows for FileReader.readAsText (in practice, tens of MB).
• Binary files are rejected.

Asset paths

Relative paths in the HTML (<img src="logo.png">) will fail to load — there's no base URL for relative paths to resolve against. Two workarounds:

1. Make paths absolute. Edit the HTML so paths are https://example.com/logo.png.
2. Inline the assets. Inline images as data: URIs, fonts as base64 in CSS. Tools like inline-html automate this.

For a quick preview where missing images are acceptable, neither is necessary.

When to use file mode vs URL mode

What still doesn't work

The same limitations as URL mode — see URL mode → What doesn't work today. The bottleneck is the spread pipeline, not the source.