What is screenplay format, and why is it so rigid?
A highly prescriptive layout — specific margins, capitalisation and element types — which exists for production reasons rather than literary ones. Every rule serves scheduling, budgeting or the physical business of shooting.
The elements, in order of appearance:
Scene heading (slugline) — INT. or EXT., the location, and DAY or NIGHT, in capitals. This single line is what a production breakdown is built from: it determines whether a scene is shot on a stage or on location, and which scenes can be grouped together.
Action, in present tense, describing only what is seen and heard. Not thoughts, not backstory — if the camera cannot record it, it does not belong.
Character name, centred and capitalised.
Parenthetical, used sparingly for delivery.
Dialogue, in a narrow column.
Transitions, now used rarely.
Why the formatting is fixed. The famous convention is that one properly formatted page runs roughly one minute of screen time — an approximation that holds well enough across a whole script to be useful. This only works if the margins and font are standardised, which is why Courier at 12 point persists: it is monospaced, so line counts are predictable. Change the layout and the estimate breaks, along with the scheduling built on it.
Capitalised names on first appearance let a producer extract every speaking part mechanically. Scene numbers are added at production and then frozen, so revisions use letters rather than renumbering. Coloured revision pages track changes on set.
What the format quietly enforces about writing: it makes internal states unwritable, forcing everything into action and speech; and because pages equal minutes, length is a structural constraint, not a stylistic preference.
Stage plays differ substantially, with stage directions serving a different function.
Television differs again by act structure, which exists around commercial breaks even where there are none.