The one-line brief: what to write for the first cut

A one-line brief gets a right first cut when it names five things: the film's shape (kind, size and length), the viewer and their problem, the one promise, the one proof to show, and the one action at the end. Leave out the mood, the music and the shot list. The maker can choose those. Only you know the five parts.

Why does a short brief need more care than a long one?

A long brief can hide a weak idea under ten sections. A one-line brief cannot. Every word in it becomes a decision in the film: what the first frame says, who is on screen, what the middle shows, and what the last frame asks. If a word is vague, the maker fills the gap with a guess, and the first cut shows you that guess.

This matters to anyone who makes marketing video without an agency: a founder with a launch film, a marketer with a product explainer, a small team with social video and ads to ship this week. You often brief a freelancer in a chat, an editor in a message, or an AI studio in a single text box. In each case the line you write is the whole brief.

The work also pays back. Google's Help page on creative guidance on YouTube cites Nielsen: creative accounts for 49% of all campaign ROI. If the creative carries that much of the result, the sentence that starts the creative is worth ten minutes of your time.

Where does the one-line brief come from?

The idea is older than chat tools. Agency briefs have always had one field that matters more than the rest: the single message. Omneky's guide to writing an ad creative brief calls it the main message, "the one thing the viewer should take away", and asks for one objective per brief. Its full template still has eleven fields, from the campaign name to how you will measure it.

Shorter formats keep only what changes the film. BAV Studios' creative brief has six fields (audience, tension, promise, angle, hook and proof), with one sentence per field and half a page in total. Its rule for the promise is plain: "The brief picks one belief shift. Not three." If any field needs a paragraph, it says, the strategy is not finished.

Video producers use the same test. Shootsta's guide to writing a video brief asks: "If the viewer remembers only one thing, what should it be?" It adds: "If you can't write it in one sentence, you haven't yet worked out what the video is about." Click.blue's guide to briefing a video editor calls that sentence the spine: "one sentence a viewer could repeat after watching."

A one-line brief takes the idea one step further. You fold the fields that change the film into a single sentence, and you trust the maker with the rest. The platforms point the same way. Google's page on the ABCDs of effective video ads says: "Avoid doing too much in your ad."

What to write in a one-line brief so the first cut is right

Write the five parts in this order. Each one decides a different piece of the film.

1. The shape: kind, size and length. "A 20-second 9:16 launch film" tells the maker the pace, the frame and the tone. A launch film, an explainer and a retargeting ad are different films, even for the same product.
2. The viewer and their problem. "For freelancers who chase late payments" picks the first words, the faces on screen and the examples. "For everyone" picks nothing.
3. The one promise. "It sends the reminders for you" is the sentence the viewer keeps. Write one. If you write two, the film tries to say both and lands neither.
4. The one proof. "Show a reminder going out" tells the maker what the middle of the film shows. A proof you can see is stronger than a claim the voice reads.
5. The ask. "End on 'Try it free'" is the last frame. Google's ABCD page puts it simply: "Say what you'd like viewers to do."

Put together, the example reads: A 20-second 9:16 launch film for Ledgerly, an invoicing app, for freelancers who chase late payments: it sends the reminders for you. Show a reminder going out. End on "Try it free". It is three short sentences and 32 words, and it is still one line of thought. Ledgerly is a made-up brand for this post.

What can I leave out?

Leave out what the maker can decide well without you: the music, the colours if your brand already has them, the transitions and the exact words of the voice. Add one of these only when it is a rule, not a taste. "No music" and "Use our blue, #2F6FEB" are rules. "Make it pop" is a taste, and it gives the maker nothing to act on.

How does each part show up in the film?

Each part has a place on the timeline, and the platforms say where. TikTok's Help page on creative best practices for performance ads says: "Introduce your content proposition in the first 3 seconds for better recall and awareness." The same page says to prioritize your hook in the first 6 seconds, and it lists sound or music and a vertical 9:16 frame among the basics.

Google adds the brand. Its ABCD page says to "introduce your brand or product from the start and maintain that presence". Its creative guidance page reports that, for Demand Gen in-stream skippable ads in the US in July 2026, having the brand visualized in the first 5 seconds drove 4% higher conversions on average. The same page reports 12% higher conversions for a human voice and 3% for supers or a text overlay. These are averages from Google's own measurement, not a promise for your film, but they tell you what to put first.

A worked example: how many seconds the proof gets

Take the example brief: a 20-second film. The promise goes in the first 3 seconds, as TikTok advises. The hook ends by second 6, and the brand is on screen by second 5, inside that hook. Give the ask the last 3 seconds. The proof gets what is left: 20 − 6 − 3 = 11 seconds. That is enough to show one reminder go out and one invoice marked paid. It is not enough to show three features. This is why the brief names one proof: the arithmetic of a short film leaves room for one.

Do the same sum for a 15-second cut: 15 − 6 − 3 = 6 seconds of proof. For a 6-second bumper there is no middle at all, so the promise and the ask are the whole film. The length in your brief is not a detail. It decides how much proof the film can carry.

What does a vague line get you, and how do I fix it?

Most first cuts go wrong for one of a few reasons, and each reason is a missing or a doubled part of the brief.

• "Make a video for our app." No shape, no viewer, no promise. The maker picks a generic length and a generic message. Fix: add the five parts, even if each is three words.
• Three promises in one line. "It's fast, cheap and secure." The film gives each a third of its time, and the viewer remembers none. Fix: pick the one your viewer cares about most, and keep the others for other versions.
• A claim with no proof. "The easiest invoicing app." The maker can only read the claim aloud. Fix: name the thing on screen that shows it: "Show an invoice sent in two taps."
• No size. The maker picks 16:9 and you wanted Reels. Fix: name the size, or ask for every size you need at once.
• A taste, not a rule. "Fun and modern." Fix: name one reference film you like, or one rule ("no stock people").
• The viewer is "everyone". The words fit no one in particular. Fix: name one group and their problem in their own words.

Can one line give me more than one film?

Yes, and it should. A good one-line brief fixes the promise and the proof, so you can change the hook and the size without a change to the film's point. TikTok suggests "between 3-5 different creatives per ad group". Three hooks on one brief, each in four sizes (9:16, 1:1, 4:5 and 16:9), make 3 × 4 = 12 files from one line. Our playbook on video ad variations for testing shows how to plan them so each test teaches you one thing.

The sizes need care too. BAV Studios gives a spec line for a video brief: "9:16, 20-25 seconds, captions burned in, soft CTA at frame 22." Captions belong in that line whenever the film may play on mute. Our post on captions for video ads has the rules. For one launch film made in four sizes from a single brief, see the Ritual Coffee showcase.

How do I write notes on the first cut?

The brief is the first note, not the last. When the first cut comes back, check it against your five parts before you react to taste. Do the first 3 seconds state the promise? Is the viewer the one you named? Does the middle show the proof? Does the last frame ask for the action? If one of these is wrong, quote the part of the brief it missed. That note is short and hard to misread.

Write each note about one moment and one change: "At 0:04, show the logo on the phone screen", not "the branding feels weak". A note with a time and a change is a brief for one shot. If you change the promise in a note, you are writing a new brief, and the film will change more than you expect.

Checklist for a one-line brief

• It names the kind of film, the size and the length.
• It names one viewer and their problem.
• It has one promise, in words a viewer would say.
• It names one proof the film can show, not only say.
• It ends with one action.
• Every extra word is a rule, not a taste.
• The length leaves time for the proof after the first 6 seconds.
• It asks for every size you need, with captions if the film plays on mute.

Questions and answers

How long should a one-line brief be?

One to three short sentences, about 30 to 50 words. The test is the parts, not the word count: if it names the shape, the viewer, the promise, the proof and the ask, it is long enough.

Should I write the script myself?

Not in the brief. Give the promise and the proof, and let the maker write the words to fit the length. If a line must be said word for word, such as a legal claim or a slogan, put it in quotes and say it is fixed.

What if I am not sure what the promise is?

Then the brief is not ready, and no maker can fix that for you. Write down the one thing a customer says when they recommend you. That sentence is often the promise.

Does the same brief work for an explainer or a launch film, not only an ad?

Yes. Change the shape and the ask. An explainer may be 60 seconds in 16:9 and end on "See how it works". The viewer, the promise and the proof stay the same parts of the line.

Write your line and see the first cut

FoxyLab makes marketing films from a chat: launch and product films, explainers, social video and ads. You paste a link or write one line, and the studio writes, voices, animates and renders the film in every size, then changes it from your notes. The FoxyLab launch showreel shows how chat in becomes video out. Write your line with the five parts above, and start your first film in the studio.