Markdown is markup you can read with your own eyes, and the format language models read best. AsciiDoc is the markup that does what Markdown does not, without leaving plain text. pandoc sits between the two, and this page says exactly what happens to an MD file on the way to becoming an AsciiDoc one.
What runs when an MD file becomes AsciiDoc
pandoc in two passes, on a machine we rent and watch. Your MD file is uploaded once, pandoc runs once, the AsciiDoc comes back, and neither file is kept. MD to AsciiDoc 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 MD into the AsciiDoc
The heading hierarchy. pandoc parses the MD file into its own document tree and writes that tree out as AsciiDoc, so a level two heading is still a level two heading and not merely bold text.
Tables, rebuilt in AsciiDoc 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 MD file through pandoc rather than through a printer.
Lists from the MD file, nesting included, plus code blocks, block quotes and links, all re-expressed in AsciiDoc.
Images: pandoc extracts them out of the MD file into a working directory and re-embeds them in the AsciiDoc, so nothing ends up pointing at a file that no longer exists.
What MD to AsciiDoc costs you
The presentation layer. pandoc does not translate the MD file into AsciiDoc, 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 MD and AsciiDoc files come from
AsciiDoc. Written at IBM in 2002 and kept alive because Markdown stops where technical documentation starts: it has no standard for tables that span pages, no admonition blocks, no way to include one file from another. AsciiDoc has all three. It is what the Linux kernel, Git and Fedora write their documentation in.
If a model is going to read the AsciiDoc
Structure is what survives from the MD file, and structure is what a model needs. MD in, AsciiDoc out, with the heading tree intact instead of flattened into one long paragraph.
MD to AsciiDoc, measured rather than promised
Running MD to AsciiDoc against the real engine with a real file, pandoc wrote 267 bytes of AsciiDoc in under a tenth of a second, machine otherwise idle. That is one MD file on one day and not an average, which is why the number is given together with the file that produced it.
The MD to AsciiDoc verdict was reached by finding a marker unique to the format, and the witness word with it, meaning the output carries a marker no other format writes, and the witness word planted in the source is still in it. Nothing can read these targets back, so both were required: the word alone would prove the text travelled, the marker alone that the shape is right. 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 AsciiDoc file has anything inside it.
The same MD file, sent somewhere else
Other outputs the probe measured out of an MD file, so the cost of choosing AsciiDoc can be read against something. Sizes do not compare across engines, because each family was probed with its own MD witness file.
MD to PDF: 25,764 bytes in 1.9 seconds, verified by a format signature.
MD to DOCX: 10,106 bytes in 0.1 seconds, verified by a pandoc round trip.
MD to EPUB: 5,034 bytes in 0.1 seconds, verified by a pandoc round trip.
MD to TXT: 264 bytes in under a tenth of a second, verified by reading the text back.
MD to HTML: 4,018 bytes in 0.1 seconds, verified by a pandoc round trip.
MD to RTF: 687 bytes in under a tenth of a second, verified by a pandoc round trip.
What we will not pretend about MD to AsciiDoc
An MD file over 25 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
An MD to AsciiDoc 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 MD to AsciiDoc 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 AsciiDoc 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 MD file goes through LibreOffice or calibre, both of which genuinely can.
One MD file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
MD to AsciiDoc: what people ask
What actually converts my MD file to AsciiDoc?
pandoc does it, in two passes, on a machine we rent and watch. Not a browser trick and not somebody else service: the MD file is uploaded once, pandoc runs once, the AsciiDoc comes back, and neither file is kept afterwards.
How long does MD to AsciiDoc take?
On the file the probe used, pandoc took under a tenth of a second and wrote 267 bytes of AsciiDoc. That is one real measurement on one real MD file, not an average and not a promise about yours: a larger MD takes longer, and past 60 seconds the run is stopped.
What do I lose going from MD to AsciiDoc?
The one to know about first: The presentation layer. pandoc does not translate the MD file into AsciiDoc, 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 MD file still tables in the AsciiDoc?
Yes. pandoc reads the MD tables into its own document tree and writes them back out in AsciiDoc syntax, so what you get is a table a machine can parse rather than a picture of one.
Is MD to AsciiDoc free?
There is a free allowance every month, and one MD to AsciiDoc 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 AsciiDoc.