The right tone for a cover letter depends less on your personal writing style and more on the company you are writing to. A letter that reads as confident and direct at a fast-moving startup can read as underprepared at a more traditional company, and the reverse is just as true.
Reading the signal in the job posting
Job postings usually tell you the tone before you write a word. A posting full of casual language, short sentences, and phrases like "we're looking for someone who..." is signaling a more relaxed, direct culture. A posting written in formal, structured corporate language is signaling the opposite. The posting itself is usually the clearest, most company-specific signal available, more reliable than general assumptions about industry or company size.
Formal tone works when
The company is large, established, or in a traditionally conservative industry like law, finance, or government. In these cases, a polished, professional register with fuller sentences reads as fitting in, not stiff. Overly casual language in this context can unintentionally signal that you have not researched the company's culture.
Confident or direct tone works when
You are applying to an early-stage company, a product or growth role, or any posting that already uses informal language itself. Matching that energy, without becoming careless, signals you understand the environment you are applying into. An overly formal letter in this context can read as out of step with how the company actually communicates.
What never changes regardless of tone: specific, relevant achievements, clear reasoning for why you fit this particular role, and no filler openers like "I am writing to apply for." Tone changes how you say it, not whether you actually say something worth reading.
When you genuinely cannot tell from the posting
Some job postings are written in a generic, templated way that does not clearly signal culture either direction. In that situation, a moderate, professional-but-warm tone is the safer default, since it is unlikely to feel out of place in either a formal or casual environment, and you can adjust in later communication once you have more signal, such as how a recruiter's emails are written.
Tone is a lever, not the whole letter
Getting tone right makes a genuinely strong letter land better. It does not fix a letter that lacks specific, relevant content. Before adjusting tone, make sure the substance, the actual achievement and the actual reasoning for fit, is solid. Tone is the finishing layer, not the foundation.