ASCII Diagram Validator

Validate and fix alignment issues in ASCII box-drawing diagrams commonly used in architecture documentation, README files, and code comments.

Self-Evolving Skill: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.

Overview

ASCII diagrams using box-drawing characters (─│┌┐└┘├┤┬┴┼ and double-line variants ═║╔╗╚╝╠╣╦╩╬) require precise column alignment. This skill provides:

1. Validation script - Detects misaligned characters with file:line:column locations
2. Actionable fixes - Specific suggestions for correcting each issue
3. Multi-file support - Validate individual files or entire directories

When to Use This Skill

Invoke when:

• Creating or editing ASCII architecture diagrams in markdown
• Reviewing documentation with box-drawing diagrams
• Fixing "diagram looks wrong" complaints
• Before committing docs/ARCHITECTURE.md or similar files
• When user mentions "ASCII alignment", "diagram alignment", or "box drawing"

Supported Characters

Single-Line Box Drawing

Corners: ┌ ┐ └ ┘
Lines:   ─ │
T-joins: ├ ┤ ┬ ┴
Cross:   ┼

Double-Line Box Drawing

Corners: ╔ ╗ ╚ ╝
Lines:   ═ ║
T-joins: ╠ ╣ ╦ ╩
Cross:   ╬

Mixed (Double-Single)

╞ ╟ ╤ ╧ ╪ ╫

Quick Start

Validate a Single File

/usr/bin/env bash << 'PREFLIGHT_EOF'
uv run ${CLAUDE_PLUGIN_ROOT}/skills/ascii-diagram-validator/scripts/check_ascii_alignment.py docs/ARCHITECTURE.md
PREFLIGHT_EOF

Validate Multiple Files

/usr/bin/env bash << 'PREFLIGHT_EOF_2'
uv run ${CLAUDE_PLUGIN_ROOT}/skills/ascii-diagram-validator/scripts/check_ascii_alignment.py docs/*.md
PREFLIGHT_EOF_2

Validate Directory

/usr/bin/env bash << 'PREFLIGHT_EOF_3'
uv run ${CLAUDE_PLUGIN_ROOT}/skills/ascii-diagram-validator/scripts/check_ascii_alignment.py docs/
PREFLIGHT_EOF_3

Output Format

The script outputs issues in a compiler-like format for easy navigation:

docs/ARCHITECTURE.md:45:12: error: vertical connector '│' at column 12 has no matching character above
  → Suggestion: Add '│', '├', '┤', '┬', or '┼' at line 44, column 12

docs/ARCHITECTURE.md:67:8: warning: horizontal line '─' at column 8 has no terminator
  → Suggestion: Add '┐', '┘', '┤', '┴', or '┼' to close the line

Severity Levels

Level	Description
error	Broken connections, misaligned verticals
warning	Unterminated lines, potential issues
info	Style suggestions (optional cleanup)

Validation Rules

The script checks for:

1. Vertical Alignment - Vertical connectors (│║) must align with characters above/below
2. Corner Connections - Corners (┌┐└┘╔╗╚╝) must connect properly to adjacent lines
3. Junction Validity - T-joins and crosses must have correct incoming/outgoing connections
4. Line Continuity - Horizontal lines (─═) should terminate at valid endpoints
5. Box Closure - Boxes should be properly closed (no dangling edges)

Exit Codes

Code	Meaning
0	No issues found
1	Errors detected
2	Warnings only (errors ignored with --warn-only)

Integration with Claude Code

When Claude Code creates or edits ASCII diagrams:

1. Run the validator script on the file
2. Review any errors in the output
3. Apply suggested fixes
4. Re-run until clean

Example Workflow

/usr/bin/env bash << 'PREFLIGHT_EOF_4'
# After editing docs/ARCHITECTURE.md
uv run ${CLAUDE_PLUGIN_ROOT}/skills/ascii-diagram-validator/scripts/check_ascii_alignment.py docs/ARCHITECTURE.md

# If errors found, Claude Code can read the output and fix:
# docs/ARCHITECTURE.md:45:12: error: vertical connector '│' at column 12 has no matching character above
# → Edit line 44, column 12 to add the missing connector
PREFLIGHT_EOF_4

Limitations

• Detects structural alignment issues, not aesthetic spacing
• Requires consistent use of box-drawing characters (no mixed ASCII like +---+)
• Tab characters may cause false positives (convert to spaces first)
• Unicode normalization not performed (use pre-composed characters)

Bundled Scripts

Script	Purpose
scripts/check_ascii_alignment.py	Main validation script

Related

• ARCHITECTURE.md best practices
• Unicode Box Drawing block

---

Troubleshooting

Issue	Cause	Solution
Script not found	Plugin not installed	Verify plugin installed with claude plugin list
False positives with tabs	Tab characters misalign	Convert tabs to spaces before validation
Mixed ASCII not detected	Using +---+ style	Script only validates Unicode box-drawing chars
Column numbers off	Unicode width calculation	Use pre-composed characters, avoid combining marks
No issues but looks wrong	Aesthetic spacing not checked	Validator checks structure, not visual spacing
Exit code 2 unexpected	warnings only mode	Use --warn-only flag to treat warnings as success
Can't find validation error	Complex nested diagram	Check line numbers in output, validate section only
Unicode chars not rendering	Terminal font missing glyphs	Use font with full Unicode box-drawing support

Post-Execution Reflection

After this skill completes, check before closing:

1. Did the command succeed? — If not, fix the instruction or error table that caused the failure.
2. Did parameters or output change? — If the underlying tool's interface drifted, update Usage examples and Parameters table to match.
3. Was a workaround needed? — If you had to improvise (different flags, extra steps), update this SKILL.md so the next invocation doesn't need the same workaround.

Only update if the issue is real and reproducible — not speculative.