Dev Markdown Check

Markdown Format Checker

Objectives

• Validate markdown syntax and structure
• Check for common formatting errors
• Ensure consistent style and conventions
• Verify links, images, and code blocks
• Improve markdown readability and quality

Quick Validation

Common Issues to Check

1. Headings:

   • Proper hierarchy (no skipped levels: H1 → H2 → H3)
   • Space after # symbols
   • Only one H1 per document
   • Consistent heading style

2. Lists:

   • Consistent bullet markers (-, *, or +)
   • Proper indentation (2 or 4 spaces)
   • Blank lines before/after lists
   • Nested lists properly indented

3. Links:

   • Valid syntax: [text](url)
   • No broken links
   • Relative paths correct
   • Reference-style links defined

4. Images:

   • Valid syntax: ![alt](path)
   • Alt text provided
   • Image files exist
   • Paths are correct

5. Code Blocks:

   • Properly fenced with ```
   • Language specified for syntax highlighting
   • Closing fence present
   • Inline code uses single backticks

6. Tables:

   • Header row present
   • Separator row with ---
   • Consistent column count
   • Proper alignment markers

7. Formatting:

   • No trailing whitespace
   • Consistent line endings
   • Blank line before/after blocks
   • Proper escaping of special characters

Validation Workflow

Step 1: Syntax Check

Read the markdown file and check for syntax errors:

def check_markdown_syntax(file_path):
    with open(file_path, 'r', encoding='utf-8') as f:
        lines = f.readlines()

    issues = []
    in_code_block = False
    code_block_start = 0

    for i, line in enumerate(lines, 1):
        # Check code blocks
        if line.strip().startswith('```'):
            if in_code_block:
                in_code_block = False
            else:
                in_code_block = True
                code_block_start = i

        # Skip checks inside code blocks
        if in_code_block:
            continue

        # Check heading format
        if line.startswith('#'):
            if not line.startswith('# ') and len(line) > 1:
                issues.append(f"Line {i}: Missing space after # in heading")

        # Check list format
        if line.strip().startswith(('-', '*', '+')):
            if not line.strip()[1:2] == ' ':
                issues.append(f"Line {i}: Missing space after list marker")

        # Check trailing whitespace
        if line.rstrip() != line.rstrip('\n'):
            issues.append(f"Line {i}: Trailing whitespace")

    # Check unclosed code blocks
    if in_code_block:
        issues.append(f"Line {code_block_start}: Unclosed code block")

    return issues

Step 2: Structure Check

Verify document structure:

def check_structure(file_path):
    with open(file_path, 'r', encoding='utf-8') as f:
        content = f.read()

    issues = []

    # Check heading hierarchy
    import re
    headings = re.findall(r'^(#{1,6})\s+(.+)$', content, re.MULTILINE)

    prev_level = 0
    for heading, text in headings:
        level = len(heading)

        # Check for skipped levels
        if level > prev_level + 1:
            issues.append(f"Heading '{text}': Skipped level (H{prev_level} → H{level})")

        # Check for multiple H1
        if level == 1 and prev_level == 1:
            issues.append(f"Multiple H1 headings found")

        prev_level = level

    return issues

Step 3: Link Validation

Check all links:

import os
from pathlib import Path

def check_links(file_path):
    with open(file_path, 'r', encoding='utf-8') as f:
        content = f.read()

    issues = []
    base_dir = Path(file_path).parent

    # Find all markdown links
    import re
    links = re.findall(r'\[([^\]]+)\]\(([^\)]+)\)', content)

    for text, url in links:
        # Skip external URLs
        if url.startswith(('http://', 'https://', 'mailto:')):
            continue

        # Check relative file paths
        if not url.startswith('#'):
            file_path = base_dir / url
            if not file_path.exists():
                issues.append(f"Broken link: [{text}]({url})")

    return issues

Common Fixes

Fix Heading Hierarchy

def fix_heading_hierarchy(content):
    """Ensure proper heading hierarchy"""
    lines = content.split('\n')
    fixed_lines = []
    prev_level = 0

    for line in lines:
        if line.startswith('#'):
            # Count heading level
            level = len(line) - len(line.lstrip('#'))

            # Fix skipped levels
            if level > prev_level + 1:
                level = prev_level + 1
                line = '#' * level + line.lstrip('#')

            prev_level = level

        fixed_lines.append(line)

    return '\n'.join(fixed_lines)

Fix List Formatting

def fix_list_formatting(content):
    """Ensure consistent list formatting"""
    lines = content.split('\n')
    fixed_lines = []

    for line in lines:
        # Fix list markers
        if line.strip().startswith(('-', '*', '+')):
            marker = line.strip()[0]
            rest = line.strip()[1:].lstrip()
            indent = len(line) - len(line.lstrip())
            fixed_lines.append(' ' * indent + f'{marker} {rest}')
        else:
            fixed_lines.append(line)

    return '\n'.join(fixed_lines)

Remove Trailing Whitespace

def remove_trailing_whitespace(content):
    """Remove trailing whitespace from all lines"""
    lines = content.split('\n')
    return '\n'.join(line.rstrip() for line in lines)

Markdown Linters

Use markdownlint (CLI)

# Install
npm install -g markdownlint-cli

# Check file
markdownlint document.md

# Fix automatically
markdownlint --fix document.md

# Check directory
markdownlint "**/*.md"

Use remark (CLI)

# Install
npm install -g remark-cli remark-preset-lint-recommended

# Check file
remark document.md

# Fix automatically
remark document.md --output

Python: markdown-it-py

uv add markdown-it-py

from markdown_it import MarkdownIt

md = MarkdownIt()
tokens = md.parse(content)

# Validate structure
for token in tokens:
    print(f"{token.type}: {token.tag}")

Best Practices

1. Consistent Style

• Use - for unordered lists
• Use **bold** not __bold__
• Use *italic* not _italic_
• Use fenced code blocks (```) not indented

2. Readability

• Add blank lines before/after headings
• Add blank lines before/after lists
• Add blank lines before/after code blocks
• Keep lines under 80-100 characters (optional)

3. Accessibility

• Provide alt text for all images
• Use descriptive link text (not "click here")
• Use proper heading hierarchy
• Add language to code blocks

4. Portability

• Use relative paths for local files
• Avoid platform-specific paths
• Use forward slashes / in paths
• Test on different markdown renderers

Validation Checklist

Before finalizing markdown:

• Run markdown linter
• Check all headings follow hierarchy
• Verify all links work
• Confirm all images display
• Test code blocks render correctly
• Check tables are properly formatted
• Remove trailing whitespace
• Ensure consistent list formatting
• Verify proper blank line spacing
• Test rendering in target platform

Quick Fix Script

def quick_fix_markdown(file_path):
    """Apply common fixes to markdown file"""
    with open(file_path, 'r', encoding='utf-8') as f:
        content = f.read()

    # Apply fixes
    content = remove_trailing_whitespace(content)
    content = fix_list_formatting(content)
    content = fix_heading_hierarchy(content)

    # Write back
    with open(file_path, 'w', encoding='utf-8') as f:
        f.write(content)

    print(f"✓ Fixed: {file_path}")

Integration with PDF Converter

After converting PDF to markdown:

1. Run syntax check
2. Fix common issues automatically
3. Validate structure
4. Check links and images
5. Generate validation report

Output Format

# Markdown Validation Report

**File:** `document.md`
**Date:** 2024-01-20

## Summary

- ✓ Syntax: Valid
- ⚠ Structure: 2 issues
- ✗ Links: 1 broken link
- ✓ Images: All valid

## Issues Found

### Structure Issues

1. Line 45: Skipped heading level (H2 → H4)
2. Line 78: Multiple H1 headings

### Broken Links

1. Line 123: `[Guide](../missing.md)` - File not found

## Recommendations

1. Fix heading hierarchy at line 45
2. Change second H1 to H2
3. Update or remove broken link at line 123

Tools Reference

For detailed linting rules: See references/linting_rules.md For style guide: See references/style_guide.md