Markdown Frontmatter Parser

Static-site frameworks all put per-page metadata in a fenced block at the top of the file, and they disagree only about the fence. This tool detects whether that block is YAML between ---, TOML between +++ or a JSON object, parses it into a plain JSON object you can paste into a migration script, and shows the rest of the file as the body with word and character counts.

The block has to be the very first thing in the file. A blank line above it, a byte-order mark left by an editor, or a stray comment and the generator stops seeing frontmatter at all — a page that suddenly has no title and no date, with the raw --- showing in the rendered output, is almost always this. It is worth checking before anything else, because the failure looks like a template bug rather than a parsing one.

The parser is deliberately small: flat keys, primitive values, bracket arrays and simple block arrays. That covers the overwhelming majority of real frontmatter without loading a full YAML implementation, and it also sidesteps a category of YAML surprise. In YAML 1.1, no is the boolean false, on and off are booleans too, and 22:22 parses as a sexagesimal integer — the reason a country field containing Norway's code has bitten so many people that the behaviour has a nickname. Here those stay strings. That is safer, but it is also a divergence: what you see in this tool is not guaranteed to be what a YAML 1.1 generator does with the same file, so treat a disagreement as a signal to quote the value explicitly rather than as a bug in either.

Numbers have the ordinary caveat. 1.20 becomes 1.2 and loses its trailing zero, so a version string needs quotes to survive as text. Dates are left as strings rather than converted, which is what you want for a migration — a date that has already been parsed once has had a time zone guessed for it, and guessing twice is worse than not guessing at all. Everything runs in your browser.