$err,hr is quite useful as is, but it only knows how to interpret built-in error codes. Happily, there is an easy way to extend it, via a section in autoexp.

All it takes is adding lines of the form –

error_code_in_decimal = the_string_you_want_displayed .

For instance, paste the following code into your autoexp.dat to decode Direct3D errors:

[hresult]
;1234=my custom error code
...
; start copying from here:
2289436696=D3DERR_WRONGTEXTUREFORMAT
2289436697=D3DERR_UNSUPPORTEDCOLOROPERATION
2289436698=D3DERR_UNSUPPORTEDCOLORARG
2289436699=D3DERR_UNSUPPORTEDALPHAOPERATION
2289436700=D3DERR_UNSUPPORTEDALPHAARG
2289436701=D3DERR_TOOMANYOPERATIONS
2289436702=D3DERR_CONFLICTINGTEXTUREFILTER
2289436703=D3DERR_UNSUPPORTEDFACTORVALUE
2289436705=D3DERR_CONFLICTINGRENDERSTATE
2289436706=D3DERR_UNSUPPORTEDTEXTUREFILTER
2289436710=D3DERR_CONFLICTINGTEXTUREPALETTE
2289436711=D3DERR_DRIVERINTERNALERROR

2289436774=D3DERR_NOTFOUND
2289436775=D3DERR_MOREDATA
2289436776=D3DERR_DEVICELOST
2289436777=D3DERR_DEVICENOTRESET
2289436778=D3DERR_NOTAVAILABLE
2289435004= D3DERR_OUTOFVIDEOMEMORY
2289436779=D3DERR_INVALIDDEVICE
2289436780=D3DERR_INVALIDCALL
2289436781=D3DERR_DRIVERINVALIDCALL
2289435164=D3DERR_WASSTILLDRAWING
141953135=D3DOK_NOAUTOGEN

2289436784=D3DERR_DEVICEREMOVED
141953141=S_NOT_RESIDENT
141953142=S_RESIDENT_IN_SHARED_MEMORY
141953143=S_PRESENT_MODE_CHANGED
141953144=S_PRESENT_OCCLUDED
2289436788=D3DERR_DEVICEHUNG
;end copy.

These were adapted from macros defined d3d9.h.  Just this week I learnt you could do the same with HRESULT codes of the CLR, and of course you could do the same for your own custom error codes.