To the letter
Definition 1 of 1
Pro Tip 1/3Absolute Adherence
This phrase emphasizes following instructions with no deviations; precision is key. 
He succeeded by studying the manual to the letter.
Pro Tip 2/3Not Just Guidelines
'To the letter' means the instructions are mandatory, not just suggestions. 
You must file the paperwork to the letter or it will be rejected.
Pro Tip 3/3Detail Focused
Using this phrase indicates that every small part matters, like in a legal document. 
The lawyer reviewed the contract to the letter before signing.