portable-text-conversion

Convert HTML and Markdown content into Portable Text blocks for Sanity. Use when migrating content from legacy CMSs, importing HTML or Markdown into Sanity, building content pipelines that ingest external content, converting rich text between formats, or programmatically creating Portable Text documents. Covers @portabletext/markdown (markdownToPortableText), @portabletext/block-tools (htmlToBlocks), custom deserializers, and the Portable Text specification for manual block construction.

Portable Text Conversion

Convert external content (HTML, Markdown) into Portable Text for Sanity. Three main approaches:

markdownToPortableText — Convert Markdown directly using @portabletext/markdown (recommended for Markdown)
htmlToBlocks — Parse HTML into PT blocks using @portabletext/block-tools (for HTML migration)
Manual construction — Build PT blocks directly from any source (APIs, databases, etc.)

Portable Text Specification

Understand the target format before converting. PT is an array of blocks:

[
  {
    "_type": "block",
    "_key": "abc123",
    "style": "normal",
    "children": [
      {"_type": "span", "_key": "def456", "text": "Hello ", "marks": []},
      {"_type": "span", "_key": "ghi789", "text": "world", "marks": ["strong"]}
    ],
    "markDefs": []
  },
  {
    "_type": "block",
    "_key": "jkl012",
    "style": "h2",
    "children": [
      {"_type": "span", "_key": "mno345", "text": "A heading", "marks": []}
    ],
    "markDefs": []
  },
  {
    "_type": "image",
    "_key": "pqr678",
    "asset": {"_type": "reference", "_ref": "image-abc-200x200-png"}
  }
]

Key rules:

Every block and span needs _key (unique within the array)
_type: "block" is for text blocks; custom types use their own _type
markDefs holds annotation data; marks on spans reference markDefs[*]._key or are decorator strings
Lists use listItem ("bullet" | "number") and level (1, 2, 3...) on regular blocks

Conversion Rules

Read the rule file matching your source format:

Markdown → Portable Text: rules/markdown-to-pt.md — @portabletext/markdown with markdownToPortableText (recommended)
HTML → Portable Text: rules/html-to-pt.md — @portabletext/block-tools with htmlToBlocks
Manual PT Construction: rules/manual-construction.md — build blocks programmatically from any source

Note: @sanity/block-tools is the legacy package name. Always use @portabletext/block-tools for new projects. The API is the same.