Parsing#

Parsing is synchronous and deterministic:

import { parseMarkdown } from '@tanstack/markdown/parser'

const document = parseMarkdown(source, {
  frontmatter: true,
  headingIds: true,
})

Input normalization#

The parser normalizes line endings before extracting frontmatter, link definitions, footnote definitions, blocks, and inline content. It does not read files, load plugins, or perform asynchronous work.

Frontmatter#

A leading --- block is extracted by default:

---
title: Small Markdown
published: true
---

# Article

document.frontmatter contains the unparsed text between delimiters. Set frontmatter: false to treat the input as ordinary Markdown.

Heading IDs#

Headings receive lowercase, duplicate-safe IDs by default. Disable them or provide a custom function:

parseMarkdown(source, { headingIds: false })

parseMarkdown(source, {
  headingIds(text, sourceLine) {
    return `${sourceLine}-${text.toLowerCase().replaceAll(' ', '-')}`
  },
})

The second callback argument is the zero-based normalized parser line index. It is not a source-location API because frontmatter and definitions may already have been extracted.

Definitions and footnotes#

Link definitions are collected before block parsing and resolved case-insensitively. Footnotes are emitted in first-reference order, with collision-safe IDs and back-reference counts.

The references, footnotes, footnoteOrder, and footnoteCounts fields in ParseOptions carry parser state through nested parsing. Most consumers should leave them unset.

Extensions#

Extensions may claim a block, transform inline nodes, transform the completed document, or render custom HTML. They run in array order. See Extensions for lifecycle and examples.

Complexity bounds#

Block recursion is capped, inline scanning uses explicit budgets, and malformed-input behavior is covered by fixed-seed fuzzing and adversarial runtime tests. Inputs beyond a parser depth limit degrade to text content instead of recursing without bound.