Formal:
* Purist: Emphasizes strict adherence to rules or standards.
* Pedant: Suggests someone who is excessively concerned with minor details or rules.
* Perfectionist: Focuses on achieving a high standard of excellence.
* Scrupulous: Highlights meticulous attention to detail and moral integrity.
* Rigorist: Implies a strict and uncompromising approach.
Informal:
* Nitpicker: Emphasizes someone who focuses on minor flaws or details.
* Detail-oriented: Highlights a focus on precision and accuracy.
* Rule follower: Emphasizes strict adherence to regulations.
* Hardliner: Suggests a stubborn and inflexible approach.
* Stick-in-the-mud: Implies someone who is resistant to change or new ideas.
The best synonym will depend on the specific context of your sentence.