Which herbs genuinely work on an indoor windowsill through winter?

Light is the constraint, and in winter most windowsills deliver far less than herbs evolved for. Mediterranean herbs in particular are full-sun plants; indoors in December they receive perhaps a tenth of what they would outdoors in June. So the realistic list is short and the realistic expectation is slow growth rather than abundance.

The ones that genuinely cope are chives, parsley, mint and, with good light, thyme. Chives tolerate cool conditions and regrow reliably after cutting. Parsley is biennial, grows steadily at moderate light and does not mind a cool room. Mint is close to indestructible and actually prefers not being in full sun, though it wants consistently damp soil. Thyme manages on a bright south sill but grows slowly and resents wet feet.

Basil, coriander and dill are the common disappointments. All three want strong light and warmth; indoors in winter basil goes leggy and pale, and coriander bolts within weeks. If you want them, a small LED grow light for twelve hours a day genuinely solves it — this is one case where the equipment does the work that the season will not.

Practical points that matter more than species choice: use pots with drainage and never let them stand in a saucer of water; keep herbs off a sill directly above a radiator, where the hot dry updraught desiccates them; and turn pots weekly since indoor plants lean hard towards a single light source.

Harvest lightly and often rather than heavily and rarely. A winter windowsill herb cannot regrow at summer speed, and cutting it hard usually finishes it.