I attended a meeting wherein I got a good look at how notes that you or your representation submit on Actors Access / Breakdown Services are seen by the folks in casting.
Here are some examples of what casting sees, copied from actual notes. I should add that notes appear in a standard sans-serif font to the folks in casting, but I include them here using a fixed-width font to illustrate a point.
1234567890123456789012345678901234567890... Sounds like a great role. I have played ... Wow this roll is not so far off from the... Sounds like the role of a lifetime. Please see my weaponry experience video ... Thanks, Joseph Currently scruffy for other project. Pe... Available for entire planned shoot perio... This sounds like a fascinating script! I... Actress has stepchildren Actually retired early after 25 years in... The Office, New Adv entures of Old Chris...
The first line is something I included to show that the cutoff is clearly 40 characters. On the last line, the submitter included an errant space after “Adv,” and you should know that the penultimate note showed “years” as “y/ears”, looking something like this:
Actually retired early after 25 y ears in...
To reiterate, what casting directors see, if they don’t click through to read the whole note, is the first 40 characters, and after about the 32nd character, words may wrap in an ugly way.
Hope this helps you submit better notes!