How to Make an Event Poster with Long, Readable Text Using AI: A Prompt Checklist

Image models are good at vibes and bad at logistics. Ask for "a jazz night poster" and you get mood lighting and a saxophone. Ask for the date, the venue, the ticket price and a two-line lineup, and the text is where things fall apart: swapped digits, invented words, a venue name that is almost right.

I treat a text-heavy poster the way I'd treat a small layout bug: define the content precisely, constrain the output, test cheaply, then ship. This post is the checklist I follow. The examples use MOSS-Image, an open-source text-to-image model from OpenMOSS (Apache-2.0) that puts weight on rendering long English and Chinese text. You can run it yourself with ComfyUI or use an online front end; the checklist is the same either way.

1. Define the content as data first

Before any prompt, write the poster's text as a structured list. It forces you to decide the hierarchy, and you can paste from it without retyping.

headline: "LATE NIGHT JAZZ"
subhead: "Live trio + open jam session"
date: "SAT 14 NOV · 8PM"
venue: "The Brick Room, 22 Canal Street"
price: "Tickets $15 at the door"
footer: "All ages until 10pm"

Rule of thumb: a poster has one headline, one supporting line, and a few short facts. If you are past six or seven text blocks, the poster is turning into a flyer, and you should either cut copy or move details to a QR code you add later in an editor.

2. Quote every string, describe everything else

The model needs to know which words are content and which words are instructions. Anything that must appear on the poster goes in double quotes. Style, layout and mood stay outside the quotes.

Template:

[poster type], [style and palette], [composition].
Large headline "<headline>".
Below it, smaller text "<subhead>".
Info block with lines "<date>", "<venue>", "<price>".
Small footer "<footer>".
[layout constraints]. No other text.

Filled-in example:

A concert poster, deep navy background with warm brass highlights,
a single saxophone silhouette on the right third.
Large bold sans-serif headline "LATE NIGHT JAZZ" across the top.
Below it, smaller text "Live trio + open jam session".
Info block on the left with lines "SAT 14 NOV · 8PM",
"The Brick Room, 22 Canal Street", "Tickets $15 at the door".
Small footer "All ages until 10pm" at the bottom edge.
High contrast text on a plain area, nothing overlapping the letters. No other text.

Two details matter here. "No other text" discourages the model from filling empty space with fake words. And "plain area, nothing overlapping the letters" keeps illustration elements away from the strings you care about.

Bilingual variant (common for community events):

A community lantern festival poster, red and gold paper-cut style.
Headline "LANTERN NIGHT 元宵灯会".
Lines "Sun 23 Feb · 6–9pm 2月23日 周日", "Riverside Park 河滨公园", "Free entry 免费入场".
Keep each English line and its Chinese line on the same row. No other text.

3. Choose the aspect ratio from the output channel

Pick the canvas from where the poster will be seen. Changing the ratio after you have proofed the text usually means proofing again, because line breaks move.

4. Test cheap, ship once: Draft vs Final

Generate a low-cost draft to check text, and only render the full-size version once the strings are correct. On the site linked below the tiers look like this:

My proofing pass is literally a diff: read every line on the Draft against the YAML from step 1. Check digits twice; dates and prices are the strings that break most often and the ones readers care about most.

5. Debug failures by isolating the line

When one line is wrong, don't regenerate the whole thing and hope. Treat it like a failing test.

If the model keeps moving blocks around, use positions instead of adjectives. MOSS-Image has an experimental layout input that accepts fixed text boxes, and some front ends expose it as a visual editor. Otherwise, state positions in plain words: "headline across the top," "info block bottom left."

6. Common mistakes

• Writing the copy inside the prompt for the first time. You'll typo it. Paste from the data block.
• Ten facts on one poster. Cut to the facts someone needs from across the street: what, when, where, how much.
• Proofing on the HD render. Expensive and slow. Proof on Drafts.
• Script-style fonts for long text. Ornate lettering breaks first. Use "bold sans-serif" for info lines and save decorative styles for the headline.
• Forgetting the channel. A 9:16 story poster with a 4:3 layout prompt crops your venue line.
• Putting brands or characters you don't own in the prompt. You are responsible for what you ask for.

Running it

Locally: MOSS-Image runs in ComfyUI if you have the hardware and patience to set up the nodes and model files.

Online: an independent, unofficial AI poster generator runs MOSS-Image in the cloud with starter prompts for posters, a layout editor, and the Draft / Final / Final HD tiers described above. New users get a free Draft to try it; paid renders use one-time credit packs from $1.99, and the images may be used commercially. It is not affiliated with OpenMOSS.

Either way, the checklist holds: content as data, quote every string, pick the ratio from the channel, proof on a Draft, debug one line at a time.