ai_debug_nav
ai_debug_nav is a console command available in all 
Source games.
The ai_debug_nav console command is a debugging tool used to examine navigation problems in NPCs. When enabled, NPCs will report their navigation decision making process to the console. It's primarily a tool used by programmers to determine where navigation problems lie. Some familiarity with the AI navigation system is needed to make use of the output.
Example
Among other output, ai_debug_nav provides useful information for the following events:
- NPCs creating navigation goals. Provides a detailed breakdown of the goal parameters.
- NPCs building routes, both succeeding & failing.
- NPCs modifying their route while walking it, usually due to simplification.
- NPCs attempting to stop their movement.
- NPCs jumping.
- NPCs disabling collision with vphysics simulated entities.
Usage
ai_debug_nav 1- Turns navigation debugging output on.
ai_debug_nav 0- Turns navigation debugging output off.
