Behavior Tree Validator

Purpose

Validate behavior trees to ensure:

• Syntactic correctness (valid Python, proper structure)
• Action availability (all actions exist in robot's action library)
• Semantic consistency (reasonable parameters, logical ordering)

When to Use This Skill

1. User reports BT not working - Diagnose execution failures
2. Debugging validation failures - Understand why BT failed validation
3. Validating manually-written BTs - Check hand-crafted behavior trees
4. Called by bt-composer - Automatically during BT generation

Workflow

Step 1: Discover Available Actions

Invoke the bt-action-discovery skill (user-level skill in ~/.claude/skills/) to get the robot's available actions from the project's action_library.

This is needed to verify all actions in the BT exist in the action library.

Step 2: Run Validation Orchestrator

python validation/orchestrator.py generated_bts/{filename}.py

This runs all three validation tiers and returns JSON results.

Step 3: Parse JSON Output

The validation returns a structured JSON response with:

• tier1_critical: Must-pass checks (syntax, structure, imports)
• tier2_important: Should-pass checks (parameters, types, ranges)
• tier3_advisory: Nice-to-have checks (semantic suggestions)

Step 4: Diagnose Errors

Use validation-reference.md (in the same directory as this SKILL.md) for:

• Complete error catalog with fixes
• Detailed tier descriptions
• Troubleshooting guide
• Individual validator usage

Step 5: Provide Fixes to User

Based on tier level:

• Tier 1 errors: Critical - BT will not execute
• Tier 2 warnings: Important - may cause unexpected behavior
• Tier 3 suggestions: Advisory - quality improvements

Validation Tiers Summary

Tier 1: Critical (Must Pass)

• Valid Python syntax
• create_root() function exists and returns Behaviour
• All imports available
• All action nodes exist in action library

Tools: validation/syntax_checker.py, validation/ros_checker.py

Tier 2: Important (Should Pass)

• Parameters within valid ranges
• Required parameters provided
• Parameter types correct

Tools: validation/orchestrator.py (constraint checking)

Tier 3: Advisory (Nice to Have)

• Reasonable action ordering
• No obvious infinite loops
• No unreachable code paths

Tools: Manual review or future LLM-as-judge

Individual Validators

Run specific validators when needed:

# Syntax and structure only
python validation/syntax_checker.py generated_bts/{filename}.py

# Action existence only
python validation/ros_checker.py generated_bts/{filename}.py

# With live ROS connection
python validation/ros_checker.py generated_bts/{filename}.py --check-live

Debugging Workflows

Problem: BT fails to execute

1. Run full validation orchestrator
2. Check Tier 1 errors (critical)
3. Verify create_root() exists
4. Check all imports are valid
5. Ensure all actions exist in action library
6. See validation-reference.md for error catalog

Problem: BT executes but behaves unexpectedly

1. Check Tier 2 warnings (parameters)
2. Verify all parameters within valid ranges
3. Check parameter types match expectations
4. Review action ordering
5. See validation-reference.md for troubleshooting

Problem: Validation passes but robot doesn't move correctly

1. Check Tier 3 suggestions (semantic)
2. Review action ordering logic
3. Verify pen up/down states
4. Check coordinate calculations
5. Ensure shapes are closed
6. See validation-reference.md for best practices

How bt-composer Uses This Skill

During BT generation workflow:

1. Generate BT code
2. Write to file
3. Run validation: python validation/orchestrator.py {file}
4. Parse JSON output
5. Decision tree:
   • Tier 1 Fail → MUST regenerate (max 3x)
   • Tier 2 Warnings → Should fix if possible
   • Tier 3 Advisory → Informational only
6. Present to user when validation passes

Detailed Reference

For complete error catalog, troubleshooting guide, and validation examples, see:

validation-reference.md (in the same directory as this SKILL.md)

This external reference includes:

• Complete validation tier descriptions
• Full error catalog with fixes
• Troubleshooting guide for common problems
• Validation JSON output format
• Individual validator usage details

Notes

• Degree of freedom: Low - Run specific validation scripts, parse output
• Always run full orchestrator - Don't rely on individual validators alone
• Fix Tier 1 first - These prevent execution
• Max 3 regeneration attempts - If still failing, simplify task

Related Skills

• bt-action-discovery - Discovers available robot actions
• bt-composer - Generates BTs and calls this validator