LH Content Converter converts content between Markdown, HTML and WordPress block markup, in any direction. It is infrastructure: it has no admin screens or content of its own, and exists so that every plugin that reads or writes content in these formats uses one engine and gets the same result.
Block conversion is done by automattic/blocks-engine-php-transformer, so Markdown or HTML lands as real, editable blocks (list items, nested lists, quotes, tables, code) rather than a lump of HTML, and anything that could not be mapped to a specific block is reported rather than silently lost. Other plugins call it through a small static PHP API.
It was previously called LH Markdown Converter, which only covered Markdown and HTML.
LH Knowledge Base, LH Tasks, LH AI Legibility, LH MCP Content Transformer and LH MCP General Abilities all depend on it, so install it alongside any of them. It needs PHP 8.2 or later, and composer install in its directory after any zip install.