RTF is rich text that almost every word processor ever written can open. HTML is the markup of the web, with native headings and tables. pandoc sits between the two, and this page says exactly what happens to an RTF file on the way to becoming an HTML one.
What runs when an RTF file becomes HTML
pandoc in two passes, on a machine we rent and watch. Your RTF file is uploaded once, pandoc runs once, the HTML comes back, and neither file is kept. RTF to HTML is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the RTF into the HTML
The heading hierarchy. pandoc parses the RTF file into its own document tree and writes that tree out as HTML, so a level two heading is still a level two heading and not merely bold text.
Tables, rebuilt in HTML syntax rather than screenshotted. That is the difference between a table a machine can read and a picture of one, and it is the whole reason to send an RTF file through pandoc rather than through a printer.
Lists from the RTF file, nesting included, plus code blocks, block quotes and links, all re-expressed in HTML.
Images: pandoc extracts them out of the RTF file into a working directory and re-embeds them in the HTML, so nothing ends up pointing at a file that no longer exists.
What RTF to HTML costs you
The presentation layer. pandoc does not translate the RTF file into HTML, it rebuilds it from its own document tree, so custom styles, page setup, headers and footers do not cross over. The structure does, and that is what the tree is made of.
Where RTF and HTML files come from
RTF. Almost everything can write it, and that is the point: an RTF is plain text you can open in a text editor and read. It was the interchange format before there was an open standard, and it survives in exports from software too old or too small to ship anything better.
If a model is going to read the HTML
Structure is what survives from the RTF file, and structure is what a model needs. RTF in, HTML out, with the heading tree intact instead of flattened into one long paragraph.
RTF to HTML, measured rather than promised
Running RTF to HTML against the real engine with a real file, pandoc wrote 3,985 bytes of HTML in 0.1 seconds, machine otherwise idle. That is one RTF file on one day and not an average, which is why the number is given together with the file that produced it.
The RTF to HTML verdict was reached by a pandoc round trip, meaning the output was read back by pandoc and had to still contain a witness word planted in the source, which proves the content travelled and not merely the container. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the HTML file has anything inside it.
The same RTF file, sent somewhere else
Other outputs the probe measured out of an RTF file, so the cost of choosing HTML can be read against something. Sizes do not compare across engines, because each family was probed with its own RTF witness file.
RTF to PDF: 11,917 bytes in 1.1 seconds, verified by a format signature.
RTF to MD: 265 bytes in under a tenth of a second, verified by a pandoc round trip.
RTF to DOCX: 5,422 bytes in 1.1 seconds, verified by a format signature.
RTF to EPUB: 5,033 bytes in 0.1 seconds, verified by a pandoc round trip.
RTF to TXT: 263 bytes in under a tenth of a second, verified by reading the text back.
RTF to ODT: 12,670 bytes in 1.2 seconds, verified by reading the internal type and finding a witness word.
Other ways into HTML, and what they measured
Among the published routes into HTML, RTF is the sixth largest output of the 12 measured. The witness files differ, so this ranks the probe run and not your document.
TXT to HTML: 3,896 bytes in 0.1 seconds.
DOC to HTML: 1,626 bytes in 1.1 seconds.
XLSX to HTML: 2,269 bytes in 1.1 seconds.
PPTX to HTML: 14,373 bytes in 1.5 seconds.
XLS to HTML: 2,101 bytes in 1.0 seconds.
What we will not pretend about RTF to HTML
An RTF file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
An RTF to HTML run that passes 60 seconds is killed, and the pandoc process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
32 of the 935 pairs probed in the family that serves RTF to HTML failed, and this pair is not one of them. They fail for reasons worth knowing: a writer that cannot carry what the document is made of, or output the engine could not read back. They are counted here rather than hidden, because a pair that fails quietly is worse than one that fails loudly.
pandoc never writes the HTML through a TeX engine here, and it never writes PDF at all: the eleven engines it would need are not on this machine and a TeX distribution weighs several gigabytes. Anyone who wants a PDF out of an RTF file goes through LibreOffice or calibre, both of which genuinely can.
One RTF file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
RTF to HTML: what people ask
What actually converts my RTF file to HTML?
pandoc does it, in two passes, on a machine we rent and watch. Not a browser trick and not somebody else service: the RTF file is uploaded once, pandoc runs once, the HTML comes back, and neither file is kept afterwards.
How long does RTF to HTML take?
On the file the probe used, pandoc took 0.1 seconds and wrote 3,985 bytes of HTML. That is one real measurement on one real RTF file, not an average and not a promise about yours: a larger RTF takes longer, and past 60 seconds the run is stopped.
What do I lose going from RTF to HTML?
The one to know about first: The presentation layer. pandoc does not translate the RTF file into HTML, it rebuilds it from its own document tree, so custom styles, page setup, headers and footers do not cross over. The structure does, and that is what the tree is made of.
Are the tables in my RTF file still tables in the HTML?
Yes. pandoc reads the RTF tables into its own document tree and writes them back out in HTML syntax, so what you get is a table a machine can parse rather than a picture of one.
Is RTF to HTML free?
There is a free allowance every month, and one RTF to HTML conversion costs half a credit against it. When the allowance runs out the tool says so and stops, rather than quietly handing you a worse HTML.