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INT. or EXT.? Scene Headings and Sluglines Explained

Every scene in a screenplay begins the same way: a short, capitalized line telling us where we are and when. That line is the scene heading — screenwriters usually call it a slugline — and it's the most structural piece of text in your script. A slugline is a promise to three different audiences at once: it tells the reader what to picture, tells the production team what to schedule and budget, and tells the editor where one scene ends and another begins. Getting INT. and EXT. right is easy. Using sluglines well is a craft skill worth twenty minutes of your attention.

The Anatomy of a Slugline

A standard scene heading has three parts, in fixed order:

INT. MERCY GENERAL HOSPITAL - ICU - NIGHT

1. INT. or EXT. — interior or exterior. This is a production question, not a mood question: is the camera under a roof on a controllable set, or outside at the mercy of weather and light? A character standing at an open window looking out is INT. A character in the yard looking in is EXT. For scenes that genuinely straddle the line — a moving car shot from inside and out, a doorway conversation — the hybrid INT./EXT. (sometimes written I/E.) exists:

INT./EXT. MOVING TRUCK - DAY

2. The location, most general to most specific, separated by dashes when you need sub-locations: MERCY GENERAL HOSPITAL - ICU. The cardinal rule here is consistency. If page 12 says INT. FRANK'S BAR - NIGHT and page 60 says INT. THE BAR - NIGHT, a production breakdown will list them as two locations, and a fast reader may genuinely wonder if they are. Name a location once, then never vary it by a single character. This matters enough that it's one of the instant amateur tells we list in our complete formatting guide.

3. Time of day, after a dash. Your defaults are DAY and NIGHT, and they should cover the vast majority of your script.

Choosing a Time of Day (and Resisting the Fancy Ones)

DAY and NIGHT are production categories: they determine when a scene can shoot and what it costs to light. The specialty options exist for when the story depends on a precise time:

  • DAWN / DUSK — only when the in-between light is the point. These are expensive, fleeting shooting windows ("magic hour" is short), so invoking them is a real ask.
  • CONTINUOUS — the scene follows directly from the previous one with no time break, usually when a character moves between spaces mid-action: INT. HALLWAY - CONTINUOUS as she storms out of the kitchen.
  • LATER — same location, same general period, time has visibly passed: INT. INTERROGATION ROOM - LATER.
  • MOMENTS LATER — a shorter skip; use sparingly or it becomes tic-like.
  • SAME — this scene happens simultaneously with the previous one, useful when cutting between two locations in parallel.

The mistake to avoid is treating the time slot as an atmosphere dial. INT. WAREHOUSE - THE DEAD OF NIGHT and EXT. BEACH - GOLDEN AFTERNOON read as writerly showing-off in the one line of the script that should be pure information. Put the atmosphere in your action lines, where it belongs.

Mini-Slugs: The Slugline's Fast Little Sibling

Inside a scene, you'll sometimes want to redirect attention or hop between sub-locations without the full ceremony of a new master slugline. That's what mini-slugs (secondary sluglines) are for — a short all-caps line, no INT./EXT., no time of day:

INT. VICTORIAN HOUSE - NIGHT

Cobwebs. Dust sheets. Claire's flashlight beam cuts the dark.

THE STAIRCASE

She climbs, each step COMPLAINING under her weight.

THE LANDING

A door stands open that was closed a moment ago.

Mini-slugs keep momentum in sequences that would otherwise be chopped into six full sluglines, and they're standard practice in produced scripts. Two guidelines: the sub-locations should all live within the master location (we're still inside the Victorian house), and when you leave for somewhere new — or time jumps — return to a full slugline. Mini-slugs are also the standard connective tissue for chases, searches, and montage sequences.

The Errors Readers Trip Over

After format basics, sluglines are where script readers most often stumble. The recurring offenders:

  1. Inconsistent location names. Covered above, and worth repeating because it's the most common slugline error in amateur scripts.
  2. Sluglines with no scene under them. A heading followed by one line of action, then another heading, then another — page after page. Sometimes a fast-cut sequence justifies this; usually it means the writer is writing a shot list, not scenes.
  3. Burying story in the slugline. INT. JIM'S APARTMENT WHERE HE HAS LIVED ALONE SINCE THE DIVORCE - NIGHT is not a location; it's an action line trying to sneak past security.
  4. Wrong INT/EXT. Porches, cars, tents, caves, stadiums — writers guess. When genuinely ambiguous, pick the one that matches where the camera mostly lives, or use INT./EXT.
  5. Orphaned time changes. Writing NIGHT when the previous scene in the same location was DAY, with nothing in the action acknowledging that hours passed. Readers notice the sun teleporting.
  6. Novelty formats. No lowercase, no bold-only-sometimes, no invented prefixes. The slugline is the last place in a screenplay to be creative.

None of this is difficult — it's bookkeeping. Which is exactly why errors here cost you: they suggest the writer didn't proofread the easiest 5% of the script, and readers extrapolate.

Let the Slugline Do Its Quiet Work

There's a deeper craft point hiding in all this bookkeeping. Because sluglines are the skeleton of your script, reading only the sluglines is a legitimate diagnostic. Scan yours in order: do locations vary, or does everything happen in apartments? Does DAY/NIGHT alternate with any rhythm, or is your whole second act nocturnal? Do we return to key locations at meaningful moments? A screenplay's slugline list is an X-ray of its visual variety — and looking at that X-ray is far easier in a proper editor than a word processor. Type INT. in a free screenwriting app like Quillit and the heading formats itself, leaving your attention free for the actual decision: where should this scene live, and when?

Master the slugline's anatomy once, keep it boring and consistent forever, and it disappears — which is the highest compliment a piece of screenplay formatting can earn. The reader stops seeing headings and starts seeing places. That's the job.