This skill builds on render-markdown. Read it first for the supported syntax, AST, parser options, and renderer contracts.

TanStack Markdown — Production Pipeline Checklist

Run every section before deploying a blog, documentation site, or user-content renderer.

Trust Boundary Checks

Check: Classify every Markdown source

Expected:

import { renderHtml } from '@tanstack/markdown/html'

export function renderUntrustedMarkdown(
  source: string,
  sanitize: (html: string) => string,
): string {
  const rendered = renderHtml(source)
  return sanitize(rendered)
}

Fail condition: Untrusted input reaches allowHtml, an unaudited extension renderHtml hook, or an unaudited highlighter.

Fix: Separate trusted and untrusted entry points, keep trusted callbacks disabled for untrusted content, and enforce application link, image, and final-HTML policy.

Highlighting Checks

Check: Return trusted code contents only

Expected:

import { renderHtml } from '@tanstack/markdown/html'
import { createHighlighter } from '@tanstack/highlight/core'
import { plaintext } from '@tanstack/highlight/languages/plaintext'
import { ts } from '@tanstack/highlight/languages/ts'
import { createTanStackMarkdownHighlighter } from '@tanstack/highlight/markdown'
const highlighter = createHighlighter({ languages: [plaintext, ts] })
export const html = renderHtml('```ts {1}\nconst answer = 42\n```', {
  highlighter: createTanStackMarkdownHighlighter(highlighter),
})

Fail condition: The callback returns a complete <pre><code> tree, does not escape source code, or comes from an unreviewed transform.

Fix: Return only escaped markup for the renderer-owned <code> contents, and run highlighting during ingestion, build, or server rendering.

Compatibility Checks

Check: Validate the actual content corpus

Expected:

MARKDOWN_CORPUS_DIRS=../site/src/blog:../site/docs pnpm run test:corpus
pnpm run corpus:audit:tanstack
pnpm run corpus:audit:external

Fail condition: Adoption relies only on CommonMark examples or a comparison table instead of the site's Markdown.

Fix: Add downstream content directories, preserve practical regressions with focused fixtures, and require renderer and bundle accounting for new syntax.

Check: Verify deterministic output

Expected:

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

const source = '# Deterministic\n\n- one\n- two'
const firstDocument = JSON.stringify(parseMarkdown(source))
const secondDocument = JSON.stringify(parseMarkdown(source))
const firstHtml = renderHtml(source)
const secondHtml = renderHtml(source)

if (firstDocument !== secondDocument || firstHtml !== secondHtml) {
  throw new Error('Markdown output is nondeterministic')
}

Fail condition: Identical source and options produce different serialized AST or HTML.

Fix: Remove time, randomness, environment state, and unstable ordering from extensions and render callbacks.

Performance and Cache Checks

Check: Parse once with final options

Expected:

import type { MarkdownDocument } from '@tanstack/markdown'
import { renderHtml } from '@tanstack/markdown/html'
import { parseMarkdown } from '@tanstack/markdown/parser'

const cache = new Map<string, MarkdownDocument>()

export function renderCachedArticle(key: string, source: string): string {
  const cacheKey = `markdown-0.0.13:${key}`
  let document = cache.get(cacheKey)
  if (!document) {
    document = parseMarkdown(source, {
      frontmatter: true,
      headingIds: true,
    })
    cache.set(cacheKey, document)
  }
  return renderHtml(document)
}

Fail condition: Stable content is reparsed per request, or parser options/extensions change after the AST is cached.

Fix: Build the AST with final parse options, version persisted cache keys, invalidate stored ASTs when node contracts change, and use only narrow entry points.

Check: Enforce bundle budgets

Expected:

pnpm run size
pnpm test -- tests/bundle-size.test.ts

Fail condition: Any measured entry exceeds its checked gzip budget or starts bundling a highlighter.

Fix: Inspect the bundle diff and justify any syntax or dependency cost before adjusting a budget.

Release Checks

Check: Run the complete package gate

Expected:

pnpm run verify

Fail condition: Tests, typechecking, build, docs validation, conformance accounting, sizes, benchmarks, or the npm dry run fail.

Fix: Resolve every gate before publishing, including HTML/React/Octane parity; audit raw HTML, highlighter output, HTML hooks, and component replacements separately.

Common Production Mistakes

CRITICAL Enabling HTML for untrusted Markdown

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

export function renderComment(source: string): string {
  return renderHtml(source, { allowHtml: true })
}

Correct:

import { renderHtml } from '@tanstack/markdown/html'

export function renderComment(source: string): string {
  return renderHtml(source)
}

allowHtml emits raw nodes and is not a sanitization step.

Source: docs/core-concepts/security.md

HIGH Returning highlighter containers

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

function escapeCode(code: string): string {
  return code.replace(/[&<>]/g, (character) => ({
    '&': '&amp;',
    '<': '&lt;',
    '>': '&gt;',
  })[character] ?? character)
}

console.log(renderHtml('```ts\nconst x = 1\n```', {
  highlighter: (code) => `<pre><code>${escapeCode(code)}</code></pre>`,
}))

Correct:

import { renderHtml } from '@tanstack/markdown/html'

function escapeCode(code: string): string {
  return code.replace(/[&<>]/g, (character) => ({
    '&': '&amp;',
    '<': '&lt;',
    '>': '&gt;',
  })[character] ?? character)
}

console.log(renderHtml('```ts\nconst x = 1\n```', {
  highlighter: (code) => `<span class="token">${escapeCode(code)}</span>`,
}))

The renderer owns <pre><code>; the callback supplies only the code element's trusted contents.

Source: docs/guides/syntax-highlighting.md

CRITICAL Trusting arbitrary highlighter output

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

const source = '```html\n<img src=x onerror=alert(1)>\n```'
console.log(renderHtml(source, { highlighter: (code) => code }))

Correct:

import { renderHtml } from '@tanstack/markdown/html'

function escapeCode(code: string): string {
  return code.replace(/[&<>]/g, (character) => ({
    '&': '&amp;',
    '<': '&lt;',
    '>': '&gt;',
  })[character] ?? character)
}

const source = '```html\n<img src=x onerror=alert(1)>\n```'
console.log(renderHtml(source, { highlighter: escapeCode }))

Highlighter output is inserted without further escaping in every renderer.

Source: docs/core-concepts/security.md

MEDIUM Bundling highlighting into static clients

Wrong:

import { Markdown } from '@tanstack/markdown/react'
import { tokenize } from '@tanstack/highlight'

export function Article({ source }: { source: string }) {
  return <Markdown highlighter={(code) => String(tokenize(code))}>{source}</Markdown>
}

Correct:

import { renderHtml } from '@tanstack/markdown/html'
import type { CodeHighlighter } from '@tanstack/markdown'

export function renderStaticArticle(
  source: string,
  highlighter: CodeHighlighter,
): string {
  return renderHtml(source, { highlighter })
}

Tokenizer runtimes, grammars, and themes can outweigh Markdown parsing and should remain build-time or server-side for static content.

Source: docs/guides/performance.md

CRITICAL Treating defaults as a sanitizer

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

export function renderForEveryPolicy(source: string): string {
  return renderHtml(source)
}

Correct:

import { renderHtml } from '@tanstack/markdown/html'

export function renderWithPolicy(
  source: string,
  sanitize: (html: string) => string,
): string {
  return sanitize(renderHtml(source))
}

Core escaping and protocol filtering do not enforce application-specific outbound-link, image, or final-HTML policy.

Source: docs/core-concepts/security.md

HIGH Assuming complete CommonMark behavior

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

export function renderArbitraryMarkdown(source: string): string {
  return renderHtml(source)
}

Correct:

import { renderHtml } from '@tanstack/markdown/html'

export function renderControlledDocs(source: string): string {
  return renderHtml(source)
}

The package implements a documented docs/blog profile, not complete CommonMark, GFM, MDX, or arbitrary plugin behavior.

Source: docs/core-concepts/syntax-profile.md

MEDIUM Reparsing unchanged content

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

export function renderRequest(source: string): string {
  return renderHtml(source)
}

Correct:

import type { MarkdownDocument } from '@tanstack/markdown'
import { renderHtml } from '@tanstack/markdown/html'
import { parseMarkdown } from '@tanstack/markdown/parser'

export function compile(source: string): MarkdownDocument {
  return parseMarkdown(source)
}

export function renderRequest(document: MarkdownDocument): string {
  return renderHtml(document)
}

String render inputs parse the complete document, while a cached MarkdownDocument skips that work.

Source: docs/core-concepts/document-model.md

HIGH Injecting HTML into React

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

export function Article({ source }: { source: string }) {
  const html = renderHtml(source)
  return <article dangerouslySetInnerHTML={{ __html: html }} />
}

Correct:

import { Markdown } from '@tanstack/markdown/react'

export function Article({ source }: { source: string }) {
  return <article><Markdown>{source}</Markdown></article>
}

The HTML string adds a trusted insertion boundary and bypasses React component replacement.

Source: docs/guides/react.md

MEDIUM Expecting fence metadata to highlight

Wrong:

import { renderHtml } from '@tanstack/markdown/html'

const source = '```ts {1}\nconst answer = 42\n```'
console.log(renderHtml(source))

Correct:

import { renderHtml } from '@tanstack/markdown/html'

function escapeCode(code: string): string {
  return code.replace(/[&<>]/g, (character) => ({
    '&': '&amp;',
    '<': '&lt;',
    '>': '&gt;',
  })[character] ?? character)
}

const source = '```ts {1}\nconst answer = 42\n```'
console.log(renderHtml(source, { highlighter: escapeCode }))

Fence metadata enters the AST, but token markup requires an external highlighter.

Source: docs/core-concepts/syntax-profile.md

Tensions

Compatibility breadth versus bundle budget

Do not maximize conformance by default. Require target-corpus evidence, renderer coverage, and measured bundle cost before adding syntax.

Rich trusted output versus untrusted-content safety

Do not enable raw HTML, extension HTML, or highlighter markup globally to solve presentation needs. Scope each trusted callback to controlled content.

Parse-ahead performance versus option timing

Build cached ASTs with final parser options and document transforms. Keep required HTML render hooks active when rendering those cached documents.

Pre-Deploy Summary

• Every content source is classified as trusted or untrusted.
• Raw HTML, extension HTML, and highlighter output have explicit owners.
• Application link, image, and final-sanitization policies are enforced.
• The downstream corpus passes deterministic AST and renderer checks.
• Unsupported syntax is documented rather than silently assumed.
• Stable content is parsed once with final options and versioned cache keys.
• Highlighting runs at build time or on the server where possible.
• Narrow entry points and individual extensions are used.
• Bundle budgets and HTML/React/Octane parity tests pass.
• pnpm run verify passes before release.

Related Skills

• render-markdown for the supported profile, AST, parser options, and core HTML rendering.
• docs-features for docs metadata and code-fence behavior.
• custom-extensions for parser hooks and trusted HTML extension boundaries.
• react-rendering and octane-rendering for framework component policy and SSR parity.