In some cases it is interesting to have access to the WAM data structures. This sub-debugger allows the user to inspect/modify the contents of any stack or register of the WAM. The WAM debugger is invoked using the built-in predicate wam_debug/0 (section 5.3.1) or the W debugger command (section 5.5). The following table presents the specific commands of the WAM debugger:
| Command | Description | 
| write A [N] | write N terms starting at the address A using write/1 (section 8.14.6) | 
| data A [N] | display N words starting at the address A | 
| modify A [N] | display and modify N words starting at the address A | 
| where A | display the real address corresponding to A | 
| what RA | display what corresponds to the real address RA | 
| deref A | display the dereferenced word starting at the address A | 
| envir [SA] | display the contents of the environment located at SA (or the current one) | 
| backtrack [SA] | display the contents of the choice-point located at SA (or the current one) | 
| backtrack all | display all choice-points | 
| quit | quit the WAM debugger | 
| help | display a summary of available commands | 
In the above table the following conventions apply:
It is possible to only use the first letters of a commands and bank names when there is no ambiguity. Also the square brackets [ ] enclosing the index of a bank name can be omitted. For instance the following command (showing the contents of 25 consecutive words of the global stack from the index 3): data global[3] 25 can be abbreviated as: d g 3 25.