Error messages and error handling in ngspice have grown over the years, include a lot of `traditional' behavior and thus are not very systematic and consistent.

Error messages may occur with the token `Error:'. Often the errors are non-recoverable and will lead to exiting ngspice with error code 1. Sometimes, however, you will get an error message, but ngspice will continue, and may either bail out later because the error has propagated into the simulation, sometimes ngspice will continue, deliver wrong results and exit with error code 0 (no error detected!).

In addition ngspice may issue warning messages like `Warning: ...'. These should cover recoverable errors only.

So there is still work to be done to define a consistent error messaging, recovery or exiting. A first step is the user definable variable strict_errorhandling. This variable may be set in files spinit (16.5) or .spiceinit (16.6) to immediately stop ngspice, after an error is detected during parsing the circuit. An error message is sent, the ngspice exit code is 1. This behavior deviates from traditional SPICE error handling and thus is introduced as an option only.

XSPICE error messages are explained in Chapt. 29.