md040.md

MD040 - Fenced code blocks should have a language specified

Tags: code, language

Aliases: fenced-code-language

Parameters:

• allowed_languages: List of languages (string[], default [])
• language_only: Require language only (boolean, default false)

This rule is triggered when fenced code blocks are used, but a language isn't specified:

```
#!/bin/bash
echo Hello world
```

To fix this, add a language specifier to the code block:

```bash
#!/bin/bash
echo Hello world
```

To display a code block without syntax highlighting, use:

```text
Plain text in a code block
```

You can configure the allowed_languages parameter to specify a list of languages code blocks could use. Languages are case sensitive. The default value is [] which means any language specifier is valid.

You can prevent extra data from being present in the info string of fenced code blocks. To do so, set the language_only parameter to true.

Info strings with leading/trailing whitespace (ex: js ) or other content (ex: ruby startline=3) will trigger this rule.

Rationale: Specifying a language improves content rendering by using the correct syntax highlighting for code. More information: https://cirosantilli.com/markdown-style-guide#option-code-fenced.