Markdown Viewer with cmux

Use this skill to display markdown files in a dedicated panel with rich formatting and live file watching. Requires cmux environment ($CMUX_WORKSPACE_ID). Outside cmux, this skill's features are unavailable.

Core Workflow

1. Write your plan or notes to a .md file.
2. Open it in a markdown panel.
3. The panel auto-updates when the file changes on disk.

# Open a markdown file as a split panel next to the current terminal
cmux markdown open plan.md

# Absolute path
cmux markdown open /path/to/PLAN.md

# Target a specific workspace
cmux markdown open design.md --workspace workspace:2

When to Use

• Displaying an agent plan or task list alongside the terminal
• Showing documentation, changelogs, or READMEs while working
• Reviewing notes that update in real-time (e.g., a plan file being written by another process)

Live File Watching

The panel automatically re-renders when the file changes on disk. This works with:

• Direct writes (echo "..." >> plan.md)
• Editor saves (vim, nano, VS Code)
• Atomic file replacement (write to temp, rename over original)
• Agent-generated plan files that are updated progressively

If the file is deleted, the panel shows a "file unavailable" state. During atomic replace, the panel retries within a short window. If the file returns later, close and reopen the panel.

Agent Integration

Opening a plan file

Write your plan to a file, then open it:

cat > plan.md << 'EOF'
# Task Plan

## Steps
1. Analyze the codebase
2. Implement the feature
3. Write tests
4. Verify the build
EOF

cmux markdown open plan.md

Updating a plan in real-time

The panel live-reloads, so simply overwrite the file as work progresses:

# The markdown panel updates automatically when the file changes
echo "## Step 1: Complete" >> plan.md

Routing

# Open in the caller's workspace (default — uses CMUX_WORKSPACE_ID)
cmux markdown open plan.md

# Open in a specific workspace
cmux markdown open plan.md --workspace workspace:2

# Open splitting from a specific surface
cmux markdown open plan.md --surface surface:5

# Open in a specific window
cmux markdown open plan.md --window window:1

Deep-Dive References

Reference	When to Use
Commands	Full command syntax and options
Live Reload	File watching behavior, atomic writes, edge cases

Rendering Support

The markdown panel renders:

• Headings (h1-h6) with dividers on h1/h2
• Fenced code blocks with monospaced font
• Inline code with highlighted background
• Tables with alternating row colors
• Ordered and unordered lists (nested)
• Blockquotes with left border
• Bold, italic, strikethrough
• Links (clickable)
• Horizontal rules
• Images (inline)

Supports both light and dark mode.

Gotchas

• File watcher does NOT auto-reconnect after a file is deleted and recreated — close and reopen the panel to pick up the new file.
• Large files (100KB+) may cause brief UI hitches during re-render. Keep plan files concise.
• Write the full plan file first, then open it — opening while still writing exposes a partially rendered state.
• Don't delete and recreate files rapidly — prefer overwriting in place or using atomic replacement (write to temp + rename).