You are hired as a developer, then on your first week you are also handling translation and some sales. Or your contract ends before your visa does, and the extension paperwork stalls. Both of those were visible in the contract before anyone signed anything.
Where you work and what you actually do
Start with the place of work and the job description. If the duties are written broadly and vaguely, being assigned something entirely different later is not a breach of anything. For a foreign employee there is a second reason to care. Work-related residence statuses are tied to the occupation that was approved, so doing work outside that scope can count as unauthorised activity. Ask for the duties to be written specifically rather than as a general category.
How hours beyond the standard week are counted
Under the Labor Standards Act contractual hours are 40 per week, with overtime allowed up to 12 hours per week. You are entitled to one paid day off per week, and once you have completed a year with sufficient attendance, 15 days of annual leave, increasing with length of service. Foreign workers are covered by the same law, so a clause offering less than this is not simply binding because you signed it. If your salary includes a fixed overtime allowance, ask for the number of hours it covers to be stated as a figure. Without that number there is no way to tell what has already been paid for.
What the salary is made of
Look at how the total splits into base pay, overtime allowance, meal allowance and transport. Two offers with the same headline figure are not equivalent: a smaller base salary shrinks the basis used to calculate severance pay and overtime, both of which are derived from it. The payment date and method belong in the contract too, and wages should go to an account in your own name.
Whether the four insurances are mentioned
National pension, health insurance, employment insurance and industrial accident insurance are known together as the four insurances. Legal employment generally means enrolment in them, and the industrial accident premium is paid entirely by the employer. Check that the contract says you will be enrolled, and how the premiums are split between you and the company.
Whether the contract period lines up with your stay
This is the line that matters most if you are not Korean. A contract that ends before your period of stay makes it harder to evidence employment when you apply to extend, and a period of stay that expires first creates the opposite problem. Put both dates side by side and sort out any mismatch before signing rather than after. You are entitled to a copy of the signed contract, so ask for one if it is not offered, and the Ministry of Employment and Labor counselling line on 1350 handles questions about working conditions.
A clause-by-clause look at the wording to expect, along with the Employment Permit System process, is in the employment contract checklist on the WeBring blog.