ASCII Table Alignment Skill

THE PROBLEM

LLMs cannot align markdown tables correctly because:

1. Token-by-token generation - No spatial awareness during output
2. Variable character widths - Even in monospace fonts:
   • CJK characters = 2 cells wide
   • Emoji = variable width
   • Combining characters = 0 width
3. No backtracking - Cannot adjust previous output based on later content

No amount of prompt engineering fixes this. The problem is fundamental to how LLMs generate text.

THE SOLUTION

Two-phase approach:

1. Generation Phase (LLM) - Focus on content, not alignment
2. Formatting Phase (Script) - wcwidth-based column alignment

MANDATORY PROTOCOL

When generating markdown tables, you MUST follow this protocol:

Step 1: Generate Table Content

Focus on correctness and completeness. Do NOT waste effort on manual alignment.

| Column A | Column B | Column C |
|---|---|---|
| Short | Much longer content here | X |
| Another row | Data | More data |

Step 2: Run Formatter (MANDATORY)

After generating any markdown table, you MUST run:

python3 ~/.claude/scripts/md-table-formatter.py /path/to/file.md

Or for stdin/stdout:

echo "table content" | python3 ~/.claude/scripts/md-table-formatter.py

Step 3: Verify Output

Check stderr for verification report:

TABLE_FORMAT_CHECK:
- Tables processed: N
- Column widths: [W1, W2, W3, ...]
- Status: ALIGNED

GENERATION GUIDELINES

When creating table content:

1. Use simple separators - |---|---|---| not |:---:|:---:|:---:|
2. Content first - Get the data right, formatting comes later
3. One table at a time - Easier to verify
4. Preserve semantics - Formatter only adjusts spacing

What the Formatter Does

• Calculates display width of each cell using wcwidth
• Finds maximum width for each column
• Pads cells with spaces to align columns
• Normalizes separator rows

What the Formatter Does NOT Do

• Change cell content
• Reorder rows/columns
• Add/remove cells
• Touch non-table content

EXAMPLES

Before Formatting

| Name | Description | Price |
|---|---|---|
| Widget | A small widget | $10.00 |
| Super Mega Deluxe Widget Pro | The ultimate widget | $99.99 |
| X | Minimal | $1 |

After Formatting

| Name                         | Description          | Price  |
|------------------------------|----------------------|--------|
| Widget                       | A small widget       | $10.00 |
| Super Mega Deluxe Widget Pro | The ultimate widget  | $99.99 |
| X                            | Minimal              | $1     |

Unicode Example (Before)

| Language | Greeting | Notes |
|---|---|---|
| English | Hello | Common |
| Japanese | こんにちは | Formal |
| Emoji | Hello! 👋 | Casual |

Unicode Example (After)

| Language | Greeting   | Notes  |
|----------|------------|--------|
| English  | Hello      | Common |
| Japanese | こんにちは | Formal |
| Emoji    | Hello! 👋  | Casual |

ERROR HANDLING

No Input Provided

Usage: md-table-formatter.py <file.md>
       cat file.md | md-table-formatter.py

Malformed Table

Tables with inconsistent column counts are skipped with a warning:

WARNING: Skipping malformed table at line 15 (inconsistent column count)

INTEGRATION WITH OTHER SKILLS

• alignment-verification: Use TABLE_FORMAT_CHECK pattern for verification output
• using-loaded-knowledge: Follow the mandatory protocol pattern (no skipping steps)

WHEN TO APPLY

ALWAYS apply when:

• Generating any markdown table
• Editing existing markdown tables
• Copying tables from external sources

DO NOT SKIP because:

• "The table is small" - Even 2x2 tables benefit
• "I'll be careful" - Manual alignment always fails
• "It looks okay" - Subjective, not measured

FAILURE MODES THIS PREVENTS

Failure: Manual Alignment Drift

| Name | Age |
|---|---|
| Alice | 30 |
| Bob | 25 |       <-- Looks aligned in editor
| Charlie | 35 |   <-- Breaks in different font

Failure: Copy-Paste Corruption

Tables from external sources have unpredictable spacing. Formatter normalizes them.

Note: Unicode Width Calculation

CJK characters are 2 cells wide. The formatter uses wcwidth if available, or a pure-Python fallback that handles common cases correctly.

ANTI-PATTERNS (FORBIDDEN)

VERIFICATION

After formatting, the script reports to stderr:

TABLE_FORMAT_CHECK:
- Tables processed: 2
- Table 1: 3 columns, widths [28, 22, 8]
- Table 2: 4 columns, widths [12, 15, 10, 8]
- Status: ALIGNED

This format follows the ALIGNMENT_CHECK pattern from alignment-verification skill.

DEPENDENCIES

Required:

• Python 3.x (standard library only)

Optional (for better CJK/emoji support):

• wcwidth library - install with one of:
  • pip3 install --user wcwidth (user install)
  • pipx install wcwidth (via pipx)
  • The script works without it using a pure-Python fallback

Script location:

• ~/.claude/scripts/md-table-formatter.py

Last Updated: 2026-02-04 Purpose: Eliminate markdown table misalignment through mandatory post-processing Success Metric: Zero misaligned tables in generated output