MMD Debugging Skill

Overview

This skill specializes in troubleshooting and debugging MIDI Markdown files. It provides systematic approaches to identify and fix errors, validation issues, and unexpected behavior.

Quick Diagnosis

When encountering an MMD error, follow this diagnostic sequence:

1. Check Syntax First

# Fast syntax check
mmdc check file.mmd

# Or use validation script
python .claude/skills/mmd-writing/scripts/validate_syntax.py file.mmd

Common syntax issues:

• Missing frontmatter (---)
• Missing timing markers before commands
• Invalid timing format
• Missing - before commands
• Missing @end after loops/aliases

2. Full Validation

# Complete validation with details
mmdc validate file.mmd --verbose

Common validation issues:

• Values out of range (>127)
• Channels outside 1-16
• Timing going backwards
• Invalid note names
• Missing required frontmatter fields

3. Inspect Events

# See what events are generated
mmdc inspect file.mmd

# Filter specific types
mmdc inspect file.mmd --type note_on
mmdc inspect file.mmd --type cc

Look for:

• Missing events
• Incorrect timing
• Wrong channels or values
• Unexpected event sequences

Error Categories

Timing Errors

Symptom: "Time X is before previous event at time Y"

Causes:

1. Timing markers not monotonically increasing
2. Loop timing overlaps
3. Using absolute timing after musical timing

Debug approach:

# Extract all timing markers
mmdc inspect file.mmd | awk '{print $1}' | sort -c

# Check if times are sequential
mmdc inspect file.mmd | head -20

Solutions:

• Use relative timing [+duration] to avoid conflicts
• Ensure absolute times increase: [00:05.000] → [00:10.000]
• Use musical timing consistently: [1.1.0] → [2.1.0]

---

Value Range Errors

Symptom: "Value X exceeds maximum allowed (Y)"

MIDI value ranges:

• Most values: 0-127
• Channels: 1-16
• Notes: 0-127 (C-1 to G9)
• Pitch bend: -8192 to +8191 or 0 to 16383

Debug approach:

# Export to CSV and check values
mmdc compile file.mmd --format csv -o debug.csv

# Find values > 127
awk -F',' '$5 > 127 {print}' debug.csv

Quick fixes:

# Wrong
- cc 1.7.255        # Max is 127

# Correct
- cc 1.7.127        # Use max value

---

Syntax Errors

Symptom: "Unexpected token at line X"

Common causes:

1. Missing dash:

   # Wrong
   [00:00.000]
   note_on 1.C4 100 1b
   
   # Correct
   [00:00.000]
   - note_on 1.C4 100 1b
   

2. Invalid timing format:

   # Wrong
   [1:30]         # Missing milliseconds
   [1-1-0]        # Wrong separator
   
   # Correct
   [00:01.500]    # mm:ss.ms
   [1.1.0]        # bar.beat.tick
   

3. Missing @end:

   # Wrong
   @loop 4 times at [1.1.0] every 1b
     - note_on 1.C4 100 1b
   # Missing @end!
   
   # Correct
   @loop 4 times at [1.1.0] every 1b
     - note_on 1.C4 100 1b
   @end
   

---

Import/Alias Errors

Symptom: "Import file not found" or "Undefined alias"

Debug approach:

# Check if device library exists
ls devices/quad_cortex.mmd

# Verify import syntax
grep "@import" file.mmd

Common issues:

1. Missing quotes: @import devices/... → @import "devices/..."
2. Wrong path: @import "quad_cortex.mmd" → @import "devices/quad_cortex.mmd"
3. Alias before import: Move @import statements before alias usage

---

Random Values Issues

Symptom: "random() not supported in this context"

NOT allowed:

[00:08.random(-10,10)]              # Timing
@define VEL random(40,60)           # Variables
- note_on 10.42.random(80,100) 1b   # Numeric note IDs

Allowed:

- note_on 1.C4 random(70,100) 0.5b  # Velocity ✓
- note_on 1.random(C3,C5) 80 0.5b   # Note range ✓
- cc 1.74.random(50,90)             # CC value ✓

---

Variable Errors

Symptom: "Variable not defined" or "Invalid variable name"

Requirements:

• Names must be UPPERCASE_WITH_UNDERSCORES
• Define before use
• Use ${} syntax for references

Debug approach:

# List all variable definitions
grep "@define" file.mmd

# List all variable uses
grep "\${" file.mmd

Example:

# Define first
@define MAIN_TEMPO 120
@define VERSE_PRESET 5

# Use later
[00:00.000]
- tempo ${MAIN_TEMPO}
- pc 1.${VERSE_PRESET}

Debugging Techniques

Binary Search for Errors

When error location is unclear:

1. Comment out half the file:

   /*
   [00:10.000]
   - note_on 1.C4 100 1b
   ...
   */
   

2. Test validation: mmdc validate file.mmd

3. If error persists: Problem is in uncommented half If error gone: Problem is in commented half

4. Repeat until error isolated

Minimal Reproduction

Create smallest file that reproduces error:

---
ppq: 480
tempo: 120
---

[00:00.000]
# Add problematic command here

This helps isolate the issue from surrounding code.

Event Inspection

Check event count:

mmdc inspect file.mmd | wc -l

Check timing distribution:

mmdc inspect file.mmd | awk '{print $1}' | sort | uniq -c

Check channels used:

mmdc inspect file.mmd | grep -o "ch:[0-9]*" | sort | uniq -c

Find specific commands:

mmdc inspect file.mmd | grep "note_on"
mmdc inspect file.mmd | grep "cc"

Comparison with Working Examples

Compare your code with similar working examples:

# Find relevant example
ls examples/

# Compare structure
diff -u examples/00_basics/01_hello_world.mmd your_file.mmd

Export and Analyze

Export to different formats for analysis:

# JSON for detailed inspection
mmdc compile file.mmd --format json -o debug.json
cat debug.json | jq '.events[] | select(.type == "note_on")'

# CSV for spreadsheet analysis
mmdc compile file.mmd --format csv -o debug.csv
# Open in spreadsheet or analyze with awk/grep

# Table for visual inspection
mmdc compile file.mmd --format table | less

Common Scenarios

Scenario 1: "No MIDI output"

Checklist:

1. ✓ Frontmatter present?
2. ✓ Timing markers before commands?
3. ✓ Commands start with - ?
4. ✓ Loops have @end?
5. ✓ File validates without errors?

Debug:

mmdc inspect file.mmd
# If no output: commands not being parsed

mmdc validate file.mmd --verbose
# Check for validation failures

---

Scenario 2: "Timing is wrong"

Checklist:

1. Mixing timing paradigms? (absolute vs musical)
2. Tempo/time_signature defined for musical timing?
3. Relative timing referencing correct previous event?
4. Loop timing makes sense?

Debug:

# Check first 20 events
mmdc inspect file.mmd | head -20

# Look for time jumps
mmdc inspect file.mmd | awk '{print $1}'

---

Scenario 3: "Loop doesn't work"

Common issues:

1. Missing @end
2. Invalid loop syntax
3. Timing conflicts

Test:

# Minimal loop test
@loop 4 times at [00:00.000] every 1b
  - note_on 1.C4 100 0.5b
@end

Debug:

# Count events (should be 4)
mmdc inspect file.mmd | grep "note_on" | wc -l

---

Scenario 4: "Device alias not working"

Checklist:

1. ✓ Import statement present?
2. ✓ Import before usage?
3. ✓ Correct device library name?
4. ✓ Correct parameter count?

Debug:

# Check imports
grep "@import" file.mmd

# Check available aliases
cat devices/quad_cortex.mmd | grep "@alias"

# Test without alias (use raw MIDI)
- cc 1.32.2  # Instead of cortex_load...

---

Scenario 5: "Validation passes but output wrong"

Possible causes:

1. Logic error (correct syntax, wrong intent)
2. Timing calculation issue
3. Device not responding as expected

Debug:

# Inspect exact events generated
mmdc inspect file.mmd

# Export to MIDI and test in DAW
mmdc compile file.mmd -o test.mid

# Play back to verify
mmdc play file.mmd --port 0

Systematic Debug Workflow

Step 1: Identify Error Type

Run validation and note error category:

• Syntax error (E1xx)
• Validation error (E2xx)
• Import/alias error (E3xx)
• Compilation error (E4xx)

Step 2: Locate Exact Line

Error messages include line numbers:

Error: Line 45: Value 255 exceeds maximum allowed (127)

Step 3: Check Context

Look at surrounding lines:

• Previous timing marker
• Related commands
• Variable definitions
• Loop/alias boundaries

Step 4: Apply Fix

Use troubleshooting guide or examples for solution.

Step 5: Verify Fix

# Validate
mmdc validate file.mmd

# Inspect events
mmdc inspect file.mmd

# Test playback
mmdc play file.mmd --port 0

Quick Fixes

Fix: Missing Frontmatter

---
ppq: 480
tempo: 120
---

Fix: Timing Going Backwards

# Use relative timing
[00:05.000]
- note_on 1.C4 100 1b

[+5s]          # Instead of absolute time
- note_on 1.D4 100 1b

Fix: Value Out of Range

# Clamp to valid range
- cc 1.7.127   # Instead of 255

Fix: Missing Timing Marker

[00:00.000]    # Add timing marker
- note_on 1.C4 100 1b

Fix: Invalid Variable Name

@define MAIN_TEMPO 120  # UPPERCASE_SNAKE_CASE

Fix: Missing Import

@import "devices/quad_cortex.mmd"

[00:00.000]
- cortex_load 1.1.0.5

Diagnostic Tools

Built-in Tools

1. mmdc check - Syntax only (fastest)
2. mmdc validate - Full validation
3. mmdc inspect - Event inspection
4. mmdc compile --format json - Detailed output

Custom Scripts

1. validate_syntax.py - Quick syntax validation

   python .claude/skills/mmd-writing/scripts/validate_syntax.py file.mmd
   

2. generate_template.py - Create working templates

   python .claude/skills/mmd-writing/scripts/generate_template.py --type basic
   

When to Ask for Help

If after following this guide you're still stuck:

1. Create minimal reproduction
2. Gather diagnostic info:
   • Error message (full text)
   • Output of mmdc validate --verbose
   • Minimal MMD file that reproduces issue
3. Check related resources (see below)
4. File GitHub issue with reproduction case

Related Skills and Resources

Skills:

• mmd-writing - MMD syntax reference
• mmd-cli - CLI tools and options
• mmd-device-library - Creating device libraries

Resources:

• TROUBLESHOOTING.md - Detailed error reference (in mmd-writing skill)
• examples/ - 49 working example files
• spec.md - Complete language specification
• docs/dev-guides/anti-patterns.md - Common mistakes to avoid

Quick Reference

Error to Solution Mapping

Error	Quick Fix
Missing frontmatter	Add ---\nppq: 480\n--- at top
No timing marker	Add [00:00.000] before first command
Timing backwards	Use relative timing [+duration]
Value > 127	Clamp to 127
Invalid channel	Use 1-16 range
Undefined alias	Add @import statement
Missing @end	Add @end after loop/alias
Invalid variable	Use UPPERCASE_SNAKE_CASE
random() not allowed	Move to velocity/note/CC value

Validation Command Matrix

Need	Command
Quick syntax check	mmdc check file.mmd
Full validation	mmdc validate file.mmd
Detailed errors	mmdc validate file.mmd --verbose
Event inspection	mmdc inspect file.mmd
JSON export	mmdc compile file.mmd --format json
CSV export	mmdc compile file.mmd --format csv

For comprehensive troubleshooting reference, see TROUBLESHOOTING.md in the mmd-writing skill directory.