A configurable command-line tool written in Rust that parses Markdown files, extracts fenced code blocks, executes them via external arbitrary commands, and optionally replaces the content of the blocks with the command output.

Useful for:

• Validating Markdown tutorials with executable code
• Auto-updating examples and documentation
• Code formatting code blocks (e.g. black, nixfmt, shfmt, php-cs-fixer, etc)
• Linting code blocks (e.g. ruff, php -l, prettier, etc)

Features

• Clean configuration via a TOML file
• Fast and dependency-free thanks to Rust
• Scans fenced Markdown code blocks by language
• Configurable per-language command execution
• Optional block replacement based on command output
• --check mode for CI/linting use cases
• Markdown code blocks can opt-out using the mdcr-skip flag
• Placeholder support ({file}, {lang}, etc.)

Installation

git clone https://github.com/drupol/markdown-code-runner
cd markdown-code-runner
cargo build --release
./target/release/mdcr --help

Via nix

Available soon through markdown-code-runner package, the binary is called mdcr.

Usage

mdcr --config config.toml path/to/file.md

Check Mode (non-destructive)

mdcr --config config.toml --check path/to/file.md

This will:

• Execute configured commands for each code block
• Fail with exit code 1 if output differs from original (like a linter)
• Do not modify files

Configuration: config.toml

The configuration file defines which commands to run for which Markdown block languages.

Example

Save this file as config.toml:

[presets.ruff-format]
languages = ["python", "py"]
command = ["ruff", "format", "-"]

[presets.nixfmt]
language = "nix"
command = ["nixfmt"]

[presets.php]
language = "php"
# php-cs-fixer does not support STDIN, so we use a temporary file
command = [
  "sh",
  "-c",
  "php-cs-fixer fix -q --rules=@PSR12 {file}; cat {file}"
]
input_mode = "file"

[presets.rust]
language = "rust"
command = ["rustfmt"]

[presets.typstyle]
language = "typst"
command = ["typstyle"]

[presets.latex]
language = "latex"
command = ["tex-fmt", "--stdin"]

Input Modes

Each preset supports an optional input_mode, which defines how the code block is passed to the command:

• stdin (default): The code is passed via standard input (STDIN)
• file: The code is written to a temporary file and its path is passed, the temporary file is deleted immediately after execution

Output Modes

Each preset also supports an optional output_mode, which defines how the command output is used:

• replace (default): Replace the code block content with the command's output
• check: Check the command's exit code, if it is different from 0, the command failed, and the tool will return a non-zero exit code

If not specified, both input_mode and output_mode default to stdin and replace, respectively.

Markdown Syntax

The tool scans for fenced code blocks like:

```python
print( "hello" )
```

It will execute all matching commands whose language is python.

Skipping a code block

To exclude a block from processing, add mdcr-skip after the language:

```python mdcr-skip
print("don't touch this")
```

Supported Placeholders

You can use placeholders in the command field:

Safeguards

• Blocks with unsupported languages are skipped with a warning.
• {file} placeholder is only available in input_mode: "file" mode.

CI Integration

Recommended usage in continuous integration:

mdcr --config config.toml --check docs/

This runs all configured checks and returns a non-zero exit code if:

• Output differs from the original
• A command fails

The --check mode will not modify any files.

Logging

The CLI option --log allows you to control the verbosity and destination of log messages emitted during execution.

Usage

mdcr --config config.toml --log debug path/to/file.md

Available log levels

The logging system uses standard log levels, from most verbose to least:

By default, if no --log option is provided, the logging level defaults to warn.