What Is a Slugline? Master and Secondary Sluglines Explained

A slugline is the line of capital letters that opens a scene in a screenplay, for example INT. KITCHEN - DAY. It is the same element as a scene heading. A master slugline carries INT./EXT., location and time; a secondary slugline is a shorter capitalised line inside a scene that shifts focus without starting a new one.

Updated 2026-09-22 · About 6 sections · 5 answered questions

What is a slugline?

A slugline is the uppercase line that starts a scene and tells the reader where and when they are. In a finished script it looks like this:

EXT. RAILWAY PLATFORM - NIGHT

The last train has gone. JUNE, 30s, sits on her suitcase and
refuses to look at the departures board.

The word comes from newspaper composing rooms, where a slug was the short identifying label on a block of type. Screenwriters borrowed it because the line does the same job: it labels the block of text beneath it. Scene heading is the term Final Draft and most books use, and it means exactly the same thing. There is no version of the industry where a slugline and a scene heading are different elements. If you want the full anatomy, the scene heading guide takes the line apart field by field; this article is about how the word is used and about the second, shorter kind of slugline that lives inside scenes.

Master sluglines: the full INT./EXT. line

A master slugline (also called a primary slugline or master scene heading) is the complete three-part line. It marks a new scene, which for a production office means a new entry in the schedule and a new number in the shooting script.

INT. GREENWAY MOTEL - ROOM 12 - NIGHT

INT. or EXT., with the period. Interior or exterior. The INT. vs EXT. article settles the awkward cases.
Location, large to small when it nests: motel, then room.
Time of day: DAY, NIGHT, CONTINUOUS, LATER, DAWN, DUSK, SAME TIME.

Every scene opens with a master slugline. Every change of location and every jump in time gets a new one. That rule has no exceptions in a spec script, and it is the rule new writers most often try to soften with a vague LATER or by simply running two locations together under one heading.

Secondary sluglines: the short line inside a scene

A secondary slugline (sub-slug, sub-heading, or mini-slug) is a capitalised line that appears inside an established scene to redirect attention without starting a new scene. It has no INT./EXT. and usually no time of day. It is a bare location, a subject, or a time jump:

INT. GREENWAY MOTEL - ROOM 12 - NIGHT

June drops her bag on the bed. Runs the tap. Nothing.

BATHROOM

A brown stain crawls up the shower curtain. She backs out.

BACK IN THE ROOM

She sits on the bed and dials.

The bathroom is part of the motel room set. Production will shoot it in the same block, on the same day, so it does not need its own master heading. The sub-slug tells the reader we have moved a few feet and tells the crew nothing they have to schedule separately.

Secondary sluglines are also how you mark a passage of time inside the same location, or single out a subject in a montage-like run:

INT. NEWSROOM - DAY

Twenty reporters on twenty phones.

LATER

Three reporters. Two phones. A pizza box.

THE WHITEBOARD

Every lead crossed out but one.

LATER on its own is accepted as a sub-slug in a spec. In a shooting script the production will usually promote it to a full heading (INT. NEWSROOM - LATER) so it can be numbered. The montage formatting article shows the same technique carrying a whole sequence.

When is a bare location line acceptable?

The test is simple: could a first assistant director shoot the new line in the same setup, on the same day, with the same lighting, as the master heading above it? If yes, a secondary slugline is fine. If no, you need a master slugline.

Situation	Use	Why
Kitchen to adjoining dining room, same house, same moment	Secondary: `DINING ROOM`	Same set, same lighting, no time passes.
Kitchen to garden, same house, same moment	Master: `EXT. GARDEN - CONTINUOUS`	Interior to exterior is always a new scene.
Same office, three hours later	Either, but `INT. OFFICE - LATER` is safer	Time jump means a lighting and continuity change.
Same office, next morning	Master: `INT. OFFICE - DAY`	Different day, different schedule entry.
Following a character through several rooms of one building at speed	Secondary for each room	Keeps the pace on the page; production groups the rooms.
Cutting to a different building across town	Master	New location, full stop.

When in doubt, use the master slugline. A reader will never mark you down for an extra full heading. They will notice a scene that quietly wanders from a living room into a car park under one INT.

Slugline mistakes that cost you reads

Sub-slugs doing the work of a master heading. THE ROOF after an INT. scene is an exterior. Give it EXT. ROOF - CONTINUOUS.
Description in the slug. INT. CRAMPED, SMOKE-STAINED KITCHEN - DAY. Cut it to INT. KITCHEN - DAY and put the smoke in the action lines, where you have room to make it vivid.
Drifting spellings. JUNE'S FLAT, JUNES APARTMENT and JUNE'S PLACE become three locations in a breakdown. Fix the string once and search for it; Zen Writer's full-script search and the free scene extractor both surface every heading in the draft so you can see the variants side by side.
Missing time of day on a master slug. A sub-slug can skip it. A master cannot.
Camera directions. ANGLE ON JUNE is not a sub-slug, it is a shot. In a spec script, write what we see as action and leave the angle to the director. The spec vs shooting script article lists what else belongs only in a production draft.
Ending every scene with CUT TO:. The next slugline is the cut. Transitions are for effects the reader would otherwise miss.
Lower case. Sluglines, master and secondary, are always uppercase.

Paste your headings into the free slugline validator and it will flag missing INT./EXT. tags, missing times of day and non-standard terms in one pass. No login, nothing uploaded.

How sluglines sit on the page

Both kinds of slugline start at the left action margin, 1.5 inches from the edge of a US Letter page, in 12-point Courier, uppercase. A blank line goes above and below. Master headings are never indented, centred, bold or underlined in a spec script. Secondary sluglines match: same margin, same case, same spacing, so the only thing that distinguishes them is the absence of INT./EXT. and a time of day.

If you write in a plain text editor, keeping sub-slugs from being mistaken for shouted action lines is up to you. Dedicated software solves it by treating the slugline as its own element type. In Zen Writer a line that begins with INT., EXT. or I/E. becomes a scene heading automatically and appears in the scene navigator, so you can jump between scenes and reorder them by dragging. Try it in the free online screenplay editor without installing anything, or on the phone where a lot of first drafts happen now.

To see master and secondary sluglines next to every other element, the formatting examples page has a full sample page, and the screenplay formatting hub covers each element on its own.

Frequently asked questions

Is a slugline the same as a scene heading?

Yes. Slugline is the older term borrowed from newspaper typesetting and scene heading is the label used by most software and manuals. They refer to the same INT./EXT. line. The only nuance is that slugline is also used for shorter secondary lines inside a scene, which nobody calls scene headings.

What is a secondary slugline?

A secondary slugline, or sub-slug, is a short uppercase line inside an established scene that shifts the reader's attention to a nearby space, a subject or a moment later, without starting a new scene. Examples are BATHROOM, THE WHITEBOARD and LATER. It has no INT./EXT. tag.

Can a slugline be just a location with no time of day?

Only as a secondary slugline inside a scene that already has a master heading with a time of day. A master slugline that starts a scene needs all three parts: INT. or EXT., the location and the time. Leaving time off a master heading is one of the most common flags in a spec.

Should secondary sluglines be used in a spec script?

Yes, in moderation. They keep chases, searches and house-tours moving without a full heading for every doorway. Use them for spaces that belong to the same set and moment. If the new space is outdoors, a different building or a different day, write a master slugline instead.

How do I write a slugline for a moving vehicle?

Use INT. CAR - DAY when the scene stays inside with the passengers and EXT. for a shot of the car on the road. If the scene moves between the two, use INT./EXT. CAR. The word MOVING or TRAVELLING after the vehicle is common in production drafts but optional in a spec.

Ready to turn this idea into a screenplay?

Zen Writer recognises INT. and EXT. as you type, formats the slugline and lists every scene in the navigator so you can reorder them by dragging.

Format Sluglines Automatically

Free on iPhone, iPad, Mac and Android.

Continue reading

Screenplay Formatting

What Is a Slugline? Master and Secondary Sluglines Explained

What is a slugline?

Master sluglines: the full INT./EXT. line

Secondary sluglines: the short line inside a scene

When is a bare location line acceptable?

Slugline mistakes that cost you reads

How sluglines sit on the page

Frequently asked questions

Ready to turn this idea into a screenplay?

Continue reading

What Is a Scene Heading?

INT. vs EXT. in a Screenplay:

How to Format a Montage in a Screenplay

Screenplay Formatting Examples:

Scene Heading (Slugline) Validator

Scene Extractor

More in screenplay formatting