eslint-plugin-markdown-preferences

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markdown-preferences/code-fence-length ​

enforce consistent code fence length in fenced code blocks.

  • ⚙️ This rule is included in plugin.configs.standard.
  • 🔧 The --fix option on the command line can automatically fix some of the problems reported by this rule.

📖 Rule Details ​

This rule enforces a consistent length for code fences (```, ~~~) in fenced code blocks. The opening and closing fence lengths must always match, regardless of configuration. This improves readability and consistency in Markdown files.

What This Rule Checks ​

  • The opening and closing code fence lengths must always match. (Always reported if not matched)
  • You can enforce a fixed fence length (e.g. always 3 backticks)
  • You can specify fallback behavior if the fixed length cannot be used (e.g. due to content)
  • You can override the length per language (info string)

Examples ​

Default (length: 3)

md
<!-- eslint markdown-preferences/code-fence-length: ['error', { "length": 3 }] -->

<!-- ✓ GOOD -->
```js
console.log("ok")
```

<!-- ✗ BAD -->

````
js
console.log("bad")
````

<!-- ✗ BAD (mismatched) -->
```js
console.log("bad")

````

With fallbackLength: "minimum"

md
<!-- eslint markdown-preferences/code-fence-length: ['error', { "length": 3, "fallbackLength": "minimum" }] -->

<!-- ✓ GOOD (content contains 3 backticks, so fence is 4) -->
````md
```
code
```
````

<!-- ✗ BAD (should use 4) -->

`````
md
```
code
```
`````

With overrides

md
<!-- eslint markdown-preferences/code-fence-length: ['error', { "length": 3, "overrides": [{ "lang": "md", "length": 4 }] }] -->

<!-- ✓ GOOD (markdown code block uses 4) -->
````md
```js
console.log("sample")
```
````

<!-- ✗ BAD (should use 4 for md) -->

```
md
# Sample
```
<!-- ✓ GOOD (js code block uses 3) -->
```js
console.log("js")
```

🔧 Options ​

json
{
  "markdown-preferences/code-fence-length": [
    "error",
    {
      "length": 3,
      "fallbackLength": "minimum",
      "overrides": [{ "lang": "md", "length": 4, "fallbackLength": "minimum" }]
    }
  ]
}
  • length (number, default: 3):
    Enforces a fixed code fence length (must be 3 or greater). The specified number of backticks (`) or tildes (~) will be used for code fences.
  • fallbackLength (number | "minimum" | "as-is", default: "minimum"):
    Specifies the fallback behavior if the fixed length cannot be used (for example, if the code block content contains a sequence of backticks/tilde of the same or greater length).
    • "minimum": Use the minimum required length (the longest sequence in the content plus one).
    • number: Use this number or the minimum required, whichever is greater.
    • "as-is": Allow the current length and do not report or fix.
  • overrides (Array<object>):
    Allows you to override length and fallbackLength for specific languages (info strings). Each item is an object with the following properties:
    • lang (string):
      The info string (language) to match for the code block (e.g., "js", "md", "sh"). If the code block's info string matches this value, this override is applied instead of the global setting.
    • length (number):
      The preferred code fence length for this language (must be 3 or greater).
    • fallbackLength (number | "minimum" | "as-is", optional):
      Fallback behavior for this language. If omitted, the global fallbackLength is used.

📚 Further Reading ​

🚀 Version ​

This rule was introduced in eslint-plugin-markdown-preferences v0.20.0

🔍 Implementation ​