The most common and most likely answer to this crossword clue is the 12 letter word SPELLCHECKER
I've seen this crossword clue in The Times
S
P
E
L
L
C
H
E
C
K
E
R
More clues leading to the result SPELLCHECKER
Buddy explains!
The straight part
We know that "Writing tool" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case writing tool = spellchecker.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SPELLCHECKER mean?
SPELLCHECKER noun- A software application that attempts to verify spelling in a document.