All four abilities are gated to the edit_posts capability (since 1.05). This is editorial tooling, so it follows the convention for editor-facing content operations rather than the install_plugins default used by developer tooling. The gate is deliberately coarse: it establishes that the caller edits content on this site and nothing more, so any ability that writes to a specific post does its own per-post check on top.
convert-to-blocks
HTML or Markdown in, serialized Gutenberg block markup out, suitable for post_content. Returns fallback diagnostics listing anything that could not be matched to a specific block and degraded to a generic wrapper, with the source tag, CSS selector and sanitized HTML for each, so the caller can see exactly what happened rather than discovering it later in the editor.
convert-from-blocks
The mirror: existing block markup in, HTML or Markdown out. Use it to read a block-based post into an editable format before revising it and converting back. Because it preserves what the blocks actually contain, the result can be converted back into equivalent blocks, which a rendered-HTML-and-regex approach cannot do.
convert-post-to-blocks
Converts an existing post’s raw-HTML content to blocks and saves it, in one server-side step. Takes only post IDs. Works on any post type. Each ID is checked individually against the caller’s edit_post capability and refused on its own if they cannot edit it, so a mixed batch reports exactly which IDs were declined instead of failing wholesale. Posts already containing block markup, and posts with empty content, are skipped rather than treated as errors. An already-published post is refused unless confirmed: true is passed on the same call.
get-pattern-guide
Static reference data describing the HTML and CSS shapes that reliably trigger the richer blocks (cover, columns, media-text, buttons), alongside the near-guaranteed plain element set. Call it before authoring HTML intended to produce a specific block, rather than guessing at markup and inspecting the fallback count afterwards. Requires no external library, since nothing in it calls the transformer.