markdown-table-validator

Markdown Table Validator

Scan Markdown files for the structural problems that silently demote a GFM table to a plain paragraph on GitHub / VS Code preview, and optionally auto-escape the single most common cause (an unescaped | inside a cell).

Self-Evolving Skill: This skill improves through use. If the detector misses a real broken-table case, the --fix heuristic guesses wrong, or a path/flag has drifted — fix this file (and the detector SSoT) immediately, don't defer. Only update for real, reproducible issues.

Why tables break (the one rule that matters)

GFM ignores whitespace between pipes, so alignment is never the cause. What breaks rendering is structure — overwhelmingly an unescaped | inside a cell. GFM's table tokenizer treats a | as a column delimiter even inside a `code span`, so a regex/code cell like `a | b | c` inflates that row's cell count and the whole table collapses. The fix — escaping it as \| — changes meaning, so no formatter does it for you (Prettier actively corrupts such tables: prettier#10164 / #11410). This skill detects it and can apply the escape under review.

Quick start

SCAN=${CLAUDE_PLUGIN_ROOT}/skills/markdown-table-validator/scripts/scan_markdown_tables.ts

# Report problems in one file (exit 1 if any render-breaking error)
bun "$SCAN" path/to/FILE.md

# Audit a whole tree
bun "$SCAN" "docs/**/*.md" "plugins/**/*.md"

# Opt-in auto-fix: escape over-count pipes, then re-align with prettier
bun "$SCAN" --fix path/to/FILE.md
prettier --write path/to/FILE.md

What it detects

Code	Severity	Meaning
column-overflow	error	A row has more cells than the header → unescaped | in a cell.
header-mismatch	error	Header and separator row have different column counts → won't render.
indented-table	error	Table indented ≥4 spaces → parsed as a code block.
alignment-colon-in-row	error	An alignment token like :--: sits in a data row (misplaced separator).
short-row	info	Row has too few cells; GFM pads and markdownlint --fix repairs.
missing-blank-line	info	No blank line before/after the table; the formatter auto-fixes.

Fenced code blocks ( ```) are skipped, so example broken tables shown inside docs don't trip the scan.

Output

Compiler-style path:line: severity: message [code]. Exit 0 when no error remains (info nits never fail the run), 1 otherwise — usable as a gate.

--fix heuristic (always review the diff)

For a row with more cells than the header, the genuine columns are assumed to be the first N; every pipe beyond column N is treated as literal content and escaped as \|. This exactly fixes the common case (regex/code in the last cell) but can guess wrong when a pipe was a genuinely missing delimiter — so review the diff, then run prettier --write to re-align.

Relationship to the automatic guard

This skill is the manual, repo-wide counterpart to the per-edit itp-hooks PostToolUse guard (posttooluse-markdown-table-guard.ts), which reminds Claude to fix the same errors the moment a .md file is written. Use the skill to clean existing docs in bulk; the hook prevents new breakage. Both share the same detection algorithm (SSoT: plugins/itp-hooks/hooks/lib/markdown-table-detector.ts).

Suppress the per-edit hook on a file by adding a comment containing MD-TABLE-OK.

References

• algorithm.md — the detection algorithm + the pipe-escaping rationale.

Post-Execution Reflection

After this skill completes, reflect before closing the task:

0. Locate yourself. — Find this SKILL.md's canonical path before editing.
1. What failed? — A missed broken table or a false positive → fix the detector (markdown-table-detector.ts) and its mirror here.
2. What worked better than expected? — Promote to recommended practice.
3. What drifted? — Keep the self-contained scanner copy in parity with the itp-hooks detector SSoT.
4. Log it. — Note the trigger, fix, and evidence.

Do NOT defer. The next invocation inherits whatever you leave behind.