ide-coverage

name	ide-coverage
description	Test coverage heatmap from lcov or JSON coverage data. Finds coverage reports, parses line coverage per file, and renders a color-coded file-tree heatmap as HTML. Opens in the system browser.
argument-hint	[path to coverage file or directory]
effort	low

Generate a visual test coverage heatmap and open it in the browser.

This skill uses only built-in tools (Glob, Read, Write, Bash) and works in both IDE-connected and remote sessions.

Arguments

$ARGUMENTS can be:

• A path to a specific coverage file (coverage/lcov.info, coverage/coverage-summary.json)
• A directory to search within (coverage/)
• Empty — auto-discover coverage files in the workspace

Steps

Phase 1 — Locate coverage data

1. If $ARGUMENTS is a specific file path, use it directly.
2. Otherwise use the Glob tool with patterns: **/lcov.info, **/coverage-summary.json, **/coverage-final.json (exclude node_modules).
3. If multiple candidates found, prefer lcov.info > coverage-summary.json > coverage-final.json. If still ambiguous (multiple projects), list them and ask the user to specify.
4. If no coverage file found: report "No coverage data found. Run npm test -- --coverage (or equivalent) first." and stop.

Phase 2 — Parse coverage

5. Use the Read tool to read the located coverage file.
6. Parse based on format:
   • lcov.info: iterate SF: (source file), LF: (lines found), LH: (lines hit) records → { file, totalLines, hitLines, pct }
   • coverage-summary.json (Istanbul/NYC): each key is a file path with { lines: { pct, total, covered } }
   • coverage-final.json: compute line pct from statement map s and statement map statementMap
7. Build a list: { file: string (relative), pct: number, hitLines: number, totalLines: number }[]
8. Group files by directory for the tree layout. Compute directory-level aggregate coverage.

Phase 3 — Generate and open HTML

9. Construct a fully self-contained HTML document (no external URLs — must work from file://) containing:
   • A summary header: "Overall coverage: N% · M / K lines covered · P files"
   • Color scale: ≥80% = #22c55e (green), ≥50% = #eab308 (yellow), <50% = #ef4444 (red), no data = #94a3b8 (grey)
   • A collapsible directory tree using <details>/<summary> HTML elements (no JS needed for expand/collapse)
   • Each file as a row: [coverage bar] filename N% (hitLines/totalLines)
   • The coverage bar is an inline <span> with a CSS width: N% background — no canvas needed
   • Directory rows show aggregate coverage for the subtree
   • A legend at the top showing the color key
   • Clicking a file's name copies its relative path to clipboard (single JS event listener, ~10 lines)
   • Page title: "Coverage — "
10. Write the HTML to coverage-<timestamp>.html in the workspace root using the Write tool.
11. Open via Bash: open coverage-<timestamp>.html (macOS) or xdg-open (Linux). If openInBrowser MCP tool is available, use that instead.
12. Report: "Opened coverage heatmap — overall N% line coverage across M files. Saved to: "

HTML constraints

• No external URLs or CDN links
• All CSS in <style>, JS limited to the clipboard copy handler
• Target 250–400 lines of HTML