rvben · chandlerc · Jul 15, 2026 · Jul 15, 2026 · Jul 15, 2026 · Jul 15, 2026
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -69,6 +69,8 @@ schemars = "1.1"
 unicode-width = "0.2"
 memory-stats = { version = "1.2.0", optional = true }
 phf = { version = "0.13", features = ["macros"] }
+markup_fmt = { version = "0.27.3", features = ["serde"], optional = true }
+dprint-plugin-typescript = { version = "0.96.1", optional = true }
 
 # LSP dependencies (native only)
 tower-lsp = { version = "0.20", optional = true }
@@ -94,7 +96,8 @@ clap_complete = "4.5.65"
 ec4rs = { version = "1.2.0", features = ["track-source"], optional = true }
 
 [features]
-default = ["parallel", "native"]
+default = ["parallel", "native", "html-fmt"]
+html-fmt = ["dep:markup_fmt", "dep:dprint-plugin-typescript"]
 parallel = ["rayon"]
 profiling = []
 native = [

diff --git a/README.md b/README.md
@@ -52,7 +52,7 @@ Python linting, rumdl brings similar speed and developer experience improvements
 It offers:
 
 - ⚡️ **Built for speed** with Rust - significantly faster than alternatives
-- 🔍 **<!-- RULE_COUNT -->82<!-- /RULE_COUNT --> lint rules** covering common Markdown issues
+- 🔍 **<!-- RULE_COUNT -->83<!-- /RULE_COUNT --> lint rules** covering common Markdown issues
 - 🛠️ **Automatic formatting** with `--fix` for files and stdin/stdout
 - 📦 **Zero dependencies** - single binary with no runtime requirements
 - 🔧 **Highly configurable** with TOML-based config files
@@ -526,7 +526,7 @@ The action ref (`rvben/rumdl@v0`) selects the GitHub Action version, while the o
 
 ## Rules
 
-rumdl implements <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> lint rules for Markdown files. Here are some key rule categories:
+rumdl implements <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> lint rules for Markdown files. Here are some key rule categories:
 
 | Category       | Description                              | Example Rules       |
 | -------------- | ---------------------------------------- | ------------------- |

diff --git a/docs/comparison.md b/docs/comparison.md
@@ -13,7 +13,7 @@ For detailed comparisons with specific tools, see:
 
 | Tool                  | Type          | Language | Rules                                     | Auto-fix | Flavors | Config format           | Plugins      | LSP |
 | --------------------- | ------------- | -------- | ----------------------------------------- | -------- | ------- | ----------------------- | ------------ | --- |
-| **rumdl**             | Lint + Format | Rust     | <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> | Yes      | 9       | TOML, JSON, YAML        | No           | Yes |
+| **rumdl**             | Lint + Format | Rust     | <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> | Yes      | 9       | TOML, JSON, YAML        | No           | Yes |
 | **markdownlint-cli**  | Lint          | Node.js  | 53                                        | Yes      | No      | JSON, JSONC, YAML, TOML | Yes (JS)     | No  |
 | **markdownlint-cli2** | Lint          | Node.js  | 53                                        | Yes      | No      | JSONC, YAML, JS         | Yes (JS)     | No  |
 | **remark-lint**       | Lint          | Node.js  | ~80 (via presets)                         | No       | No      | JS, JSON, YAML          | Yes (JS)     | No  |
@@ -33,7 +33,7 @@ cover common cases. No built-in auto-fix for lint violations (remark itself can
 
 **mado** is a Rust-based linter with 38 rules (33 stable, 5 unstable). It has no auto-fix and no plugin system.
 
-**rumdl** implements all 53 markdownlint rules plus <!-- RULE_COUNT_ADDITIONAL -->29<!-- /RULE_COUNT_ADDITIONAL --> additional rules (<!-- RULE_COUNT -->82<!-- /RULE_COUNT --> total). It supports
+**rumdl** implements all 53 markdownlint rules plus <!-- RULE_COUNT_ADDITIONAL -->30<!-- /RULE_COUNT_ADDITIONAL --> additional rules (<!-- RULE_COUNT -->83<!-- /RULE_COUNT --> total). It supports
 auto-fix for most rules and includes rules not found in other tools, such as relative link validation (MD057), footnote checks (MD066-MD068), nested code fence detection (MD070), and TOC validation
 (MD073).
 
@@ -136,7 +136,7 @@ Cold start benchmark on the Rust Book (478 Markdown files), measured with [hyper
 
 **Notes:**
 
-- **mado** is faster in cold-start benchmarks because it does less work per file: fewer rules (38 vs <!-- RULE_COUNT -->82<!-- /RULE_COUNT -->), no fix generation, and no flavor detection.
+- **mado** is faster in cold-start benchmarks because it does less work per file: fewer rules (38 vs <!-- RULE_COUNT -->83<!-- /RULE_COUNT -->), no fix generation, and no flavor detection.
   The gap reflects feature surface area, not implementation quality.
 - **rumdl** supports result caching (`rumdl check` without `--no-cache`), which skips unchanged files on subsequent runs — typically under 50 ms, faster than mado's cold start.
 - **pymarkdown** performs well for a Python tool due to its efficient scanner architecture.
@@ -147,5 +147,5 @@ Cold start benchmark on the Rust Book (478 Markdown files), measured with [hyper
 
 - [Comparison with markdownlint](markdownlint-comparison.md) — detailed rule-by-rule comparison and migration guide
 - [Comparison with mdformat](mdformat-comparison.md) — formatting feature comparison and migration guide
-- [Rules Reference](rules.md) — complete list of rumdl's <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> rules
+- [Rules Reference](rules.md) — complete list of rumdl's <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> rules
 - [Markdown Flavors](flavors.md) — flavor configuration and per-rule adjustments
diff --git a/docs/configuration/index.md b/docs/configuration/index.md
@@ -10,6 +10,8 @@ Looking for something more specific?
   [Global Settings](../global-settings.md).
 - For per-document overrides via HTML comments, see
   [Inline Configuration](../inline-configuration.md).
+- For formatting HTML and scripts embedded in Markdown, see
+  [Embedded HTML Formatting](../embedded-html-formatting.md).
 
 ## Supported config files
 

diff --git a/docs/embedded-html-formatting.md b/docs/embedded-html-formatting.md
@@ -0,0 +1,85 @@
+# Embedded HTML Formatting
+
+rumdl includes built-in support for checking and formatting HTML blocks embedded inside your Markdown files. It can also format JavaScript and TypeScript code blocks inside `<script>` tags within
+those HTML blocks.
+
+All formatting is done directly in Rust via library calls (using the `markup_fmt` and `dprint-plugin-typescript` crates), without spawning any external subprocesses.
+
+## Overview
+
+- **Lint Mode** (`rumdl check`): Validates that HTML blocks and `<script>` blocks inside them are correctly formatted, emitting warnings if not.
+- **HTML Formatting**: Handled by `markup_fmt`.
+- **Script Formatting**: Handled by `dprint-plugin-typescript` (supports JS, TS, JSX, TSX).
+- **Subprocess-free**: Fast execution, entirely integrated into the binary.
+
+## Configuration
+
+Configure HTML formatting in the `[html]` section of your `rumdl.toml` (or `pyproject.toml` under `[tool.rumdl.html]`):
+
+```toml
+[html]
+# Master switch for HTML checking and formatting (default: true)
+enabled = true
+
+# Target line width for the HTML formatter (default: 80)
+print-width = 80
+
+# Indentation size for the HTML formatter (default: 2)
+indent-width = 2
+
+# Use tab characters for indentation (default: false)
+use-tabs = false
+
+# Quote character preference for HTML attributes: "double" or "single" (default: "double")
+quotes = "double"
+
+[html.script]
+# Whether to format JavaScript/TypeScript inside <script> tags (default: true)
+enabled = true
+
+# Semicolon style preference: "always", "prefer", or "asi" (default: "prefer")
+semi-colons = "prefer"
+
+# Quote style preference: "always-double", "always-single", "prefer-double", or "prefer-single" (default: "prefer-double")
+quote-style = "prefer-double"
+```
+
+## Behavior
+
+- **Block-level Only**: rumdl only formats HTML *blocks* (blocks of HTML parsed by the Markdown parser, such as a `<div>` starting on its own line). Inline HTML tags (like `This is <b>bold</b>`) are
+    ignored to prevent layout disruptions.
+- **JSX/Component Skipping**: In MDX documents, component tags (tags starting with an uppercase letter, e.g., `<Header />` or `<MyComponent>`) are recognized as JSX and automatically skipped,
+    preventing the HTML parser from failing on non-standard tags.
+- **Error Resiliency**: If an HTML block contains malformed HTML that fails to parse, rumdl skips formatting that block rather than failing the entire linting run.
+
+## Example
+
+Given the following unformatted Markdown:
+
+```markdown
+Some text.
+
+<div class="container">
+<p>Hello World</p>
+  <script>
+const a=1;
+  const b = "double";
+  </script>
+</div>
+```
+
+Running `rumdl check` will emit warnings pointing to the HTML block starting at `<div class="container">` and the script block inside it.
+
+Running `rumdl check --fix` will format the block in-place:
+
+```markdown
+Some text.
+
+<div class="container">
+  <p>Hello World</p>
+  <script>
+    const a = 1;
+    const b = 'double';
+  </script>
+</div>
+```
diff --git a/docs/getting-started/quickstart.md b/docs/getting-started/quickstart.md
@@ -145,5 +145,5 @@ Each line shows:
 ## Next Steps
 
 - [CLI Commands](../usage/cli.md) - Full command reference
-- [Rules Reference](../rules.md) - Explore all <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> rules
+- [Rules Reference](../rules.md) - Explore all <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> rules
 - [Configuration](../global-settings.md) - Advanced configuration options
diff --git a/docs/global-settings.md b/docs/global-settings.md
@@ -1557,3 +1557,4 @@ find . -name "*.md" -o -name "*.markdown" | head -10
 - [CLI Reference](../README.md#command-line-interface) - Command-line options
 - [Rule-specific Configuration](../README.md#configuration-file-example) - Configuring individual rules
 - [Code Block Tools](code-block-tools.md) - External linters/formatters for code blocks [preview]
+- [Embedded HTML Formatting](embedded-html-formatting.md) - Built-in checking and formatting of HTML and script blocks
diff --git a/docs/index.md b/docs/index.md
@@ -16,7 +16,7 @@ icon: lucide/file-check
 
     [:octicons-arrow-right-24: Benchmarks](#performance)
 
--   :mag:{ .lg .middle } **<!-- RULE_COUNT -->82<!-- /RULE_COUNT --> lint rules**
+-   :mag:{ .lg .middle } **<!-- RULE_COUNT -->83<!-- /RULE_COUNT --> lint rules**
 
     ---
 
@@ -76,7 +76,7 @@ With intelligent caching, subsequent runs are even faster - rumdl only re-lints
 ## Features
 
 - :zap: **Built for speed** with Rust - significantly faster than alternatives
-- :mag: **<!-- RULE_COUNT -->82<!-- /RULE_COUNT --> lint rules** covering common Markdown issues
+- :mag: **<!-- RULE_COUNT -->83<!-- /RULE_COUNT --> lint rules** covering common Markdown issues
 - :wrench: **Automatic formatting** with `--fix` for files and stdin/stdout
 - :package: **Zero dependencies** - single binary with no runtime requirements
 - :gear: **Highly configurable** with TOML-based config files
@@ -100,7 +100,7 @@ With intelligent caching, subsequent runs are even faster - rumdl only re-lints
 
 -   [:octicons-book-24: **Rules Reference**](rules.md)
 
-    Explore all <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> linting rules with examples.
+    Explore all <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> linting rules with examples.
 
 -   [:octicons-gear-24: **Configuration**](global-settings.md)
 

diff --git a/docs/markdownlint-comparison.md b/docs/markdownlint-comparison.md
@@ -10,22 +10,22 @@ rumdl offers **high markdownlint compatibility with intentional differences** wh
 
 - **Performance**: rumdl is significantly faster (30-100x in many cases) thanks to Rust and intelligent caching
 - **Rule Coverage**: All 53 markdownlint rules are implemented, with a small number of intentional behavioral differences documented below
-- **Unique Features**: <!-- RULE_COUNT_ADDITIONAL -->29<!-- /RULE_COUNT_ADDITIONAL --> additional rules (MD057, MD061-<!-- RULE_MAX -->MD088<!-- /RULE_MAX -->), built-in LSP server, VS Code extension, 6 Markdown flavors
+- **Unique Features**: <!-- RULE_COUNT_ADDITIONAL -->30<!-- /RULE_COUNT_ADDITIONAL --> additional rules (MD057, MD061-<!-- RULE_MAX -->MD089<!-- /RULE_MAX -->), built-in LSP server, VS Code extension, 6 Markdown flavors
 - **Configuration**: Automatic markdownlint config discovery and conversion
 
 ## Rule Coverage
 
 ### Implemented Rules
 
-rumdl implements **<!-- RULE_COUNT -->82<!-- /RULE_COUNT --> rules total**: all 53 markdownlint rules plus <!-- RULE_COUNT_ADDITIONAL -->29<!-- /RULE_COUNT_ADDITIONAL --> unique rules.
+rumdl implements **<!-- RULE_COUNT -->83<!-- /RULE_COUNT --> rules total**: all 53 markdownlint rules plus <!-- RULE_COUNT_ADDITIONAL -->30<!-- /RULE_COUNT_ADDITIONAL --> unique rules.
 
 **Markdownlint-compatible rules (53):** All markdownlint rules are implemented with full compatibility. See the [Rules Reference](rules.md) for the complete list.
 
 **Note:** Rule numbers MD001-MD060 have gaps (MD002, MD006, MD008, MD015-MD017 were never implemented in markdownlint). rumdl maintains these gaps for compatibility.
 
 ### Rules Unique to rumdl
 
-rumdl implements <!-- RULE_COUNT_ADDITIONAL -->29<!-- /RULE_COUNT_ADDITIONAL --> additional rules not found in markdownlint:
+rumdl implements <!-- RULE_COUNT_ADDITIONAL -->30<!-- /RULE_COUNT_ADDITIONAL --> additional rules not found in markdownlint:
 
 | Rule   | Name                           | Description                                                |
 | ------ | ------------------------------ | ---------------------------------------------------------- |

diff --git a/docs/md089.md b/docs/md089.md
@@ -0,0 +1,52 @@
+# MD089 - Embedded HTML blocks should be formatted
+
+Aliases: `embedded-html-fmt`
+
+This rule is enabled by default.
+
+## What this rule does
+
+Formats HTML blocks using `markup_fmt`. It can also format JavaScript/TypeScript inside `<script>` tags and Markdown inside HTML comments if configured.
+
+## Why this matters
+
+Consistent formatting improves readability of HTML blocks embedded in Markdown documents.
+
+## Examples
+
+### Incorrect
+
+```markdown
+<div>
+<p>Unformatted HTML</p>
+  </div>
+```
+
+### Correct
+
+```markdown
+<div>
+  <p>Formatted HTML</p>
+</div>
+```
+
+## Configuration
+
+This rule is configured via the `[html]` section in the configuration file.
+
+Options:
+- `enabled`: Enable or disable the rule (boolean, default: true)
+- `print_width`: Maximum line width for formatting (integer, default: 80)
+- `use_tabs`: Use tabs for indentation (boolean, default: false)
+- `indent_width`: Indentation width (integer, default: 2)
+- `quotes`: Quote style ("double" or "single", default: "double")
+- `format_comments_as_markdown`: Format Markdown inside HTML comments (boolean, default: false)
+
+Script formatting options (via `[html.script]`):
+- `enabled`: Enable script formatting (boolean, default: false)
+- `semi_colons`: Semicolon style ("always", "prefer", "asi", default: "always")
+- `quote_style`: Quote style ("always-double", "always-single", "prefer-double", "prefer-single", default: "prefer-double")
+
+## Automatic fixes
+
+This rule supports automatic fixes. Running `rumdl --fix` or `rumdl fmt` will format the HTML blocks in place.
diff --git a/docs/mdformat-comparison.md b/docs/mdformat-comparison.md
@@ -7,7 +7,7 @@ This document compares rumdl and mdformat, focusing on their formatting capabili
 Both tools format Markdown files, but serve different purposes:
 
 - **mdformat**: Pure formatter focused on consistent Markdown output
-- **rumdl**: Combined linter and formatter with <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> rules plus formatting
+- **rumdl**: Combined linter and formatter with <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> rules plus formatting
 
 **Key Differences:**
 
@@ -16,7 +16,7 @@ Both tools format Markdown files, but serve different purposes:
 | Primary purpose | Formatting only           | Linting + formatting            |
 | Language        | Python                    | Rust                            |
 | Performance     | Good                      | Faster (native + caching)       |
-| Linting rules   | ❌                        | ✅ <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> rules                     |
+| Linting rules   | ❌                        | ✅ <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> rules                     |
 | Extensibility   | Plugin ecosystem          | Built-in flavors                |
 | CommonMark      | Strict compliance         | Strict compliance               |
 
@@ -47,7 +47,7 @@ Both tools format Markdown to a consistent style:
 
 ### Linting (rumdl only)
 
-rumdl provides <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> linting rules that mdformat does not have:
+rumdl provides <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> linting rules that mdformat does not have:
 
 - **Broken link detection** (MD051, MD052, MD057)
 - **Accessibility checks** (MD045 - image alt text)
@@ -299,7 +299,7 @@ style = "atx"
 | Capability              | mdformat           | rumdl                  |
 | ----------------------- | ------------------ | ---------------------- |
 | Markdown formatting     | ✅ Primary focus   | ✅ Via `rumdl fmt`     |
-| Markdown linting        | ❌                 | ✅ <!-- RULE_COUNT -->82<!-- /RULE_COUNT --> rules            |
+| Markdown linting        | ❌                 | ✅ <!-- RULE_COUNT -->83<!-- /RULE_COUNT --> rules            |
 | Performance             | Good               | Faster (native binary) |
 | Extended syntax         | Plugins            | Built-in flavors       |
 | Editor integration      | Basic              | LSP + VS Code          |

diff --git a/docs/playground.md b/docs/playground.md
@@ -22,7 +22,9 @@ Try rumdl directly in your browser — no installation needed. Powered by [rumdl
       <option value="links">Links and images</option>
       <option value="clean">Clean document</option>
     </select>
-    <button id="pg-fix-btn" class="pg-btn pg-btn-primary" disabled>Fix all</button>
+    <button id="pg-fix-btn" class="pg-btn pg-btn-primary" disabled>
+      Fix all
+    </button>
     <button id="pg-clear-btn" class="pg-btn">Clear</button>
   </div>
 </div>
@@ -33,7 +35,12 @@ Try rumdl directly in your browser — no installation needed. Powered by [rumdl
       <span>Markdown input</span>
       <span id="pg-char-count" class="pg-meta"></span>
     </div>
-    <textarea id="pg-input" class="pg-editor" spellcheck="false" placeholder="Type or paste markdown here…"></textarea>
+    <textarea
+      id="pg-input"
+      class="pg-editor"
+      spellcheck="false"
+      placeholder="Type or paste markdown here…"
+    ></textarea>
   </div>
   <div class="pg-panel">
     <div class="pg-panel-header">