Toolshed

YAML to JSON. POST a YAML document; the response is pretty-printed JSON. Anchors and aliases are resolved, and a multi-document stream converts as its FIRST document rather than as an array — the direction that bites, because YAML is the larger language.

JSON to YAML. POST any JSON value; the response is block-style YAML — the readable, indented form, not flow style. Any top-level shape is accepted, not just an object. There are no comments to preserve in either direction, because JSON has none.

HTML to Markdown. POST a saved page or an HTML fragment; the response is Markdown with ATX headings and fenced code. The page is parsed with a real DOM, so structure survives — but nav, ads and cookie banners convert too: pre-strip if you only want the article body.

CSV to JSON. POST a CSV file with a header row; the response is an array of objects keyed by that row. RFC 4180, so quoted commas and embedded newlines survive. Short rows are padded; a row with MORE fields than the header is an error, never a silent truncation.

NDJSON to a JSON array. POST newline-delimited JSON; the response is a pretty-printed array of the parsed values. Blank lines are skipped and a line that does not parse is refused naming the 1-based line number — which is the reason to run a parser over a log file instead of wrapping it in brackets.