advent.center: Moving Every Carousel onto ppl.studio's Deck Engine

The site and the job

advent.center catalogues advent calendars: what is inside each one, what the contents are worth, which launched this week. In season it turns those records into social carousels for TikTok, Instagram, Facebook and Pinterest, on a routine that runs every four hours. Its carousels come in nine formats, among them “what's inside”, “launched this week”, a top six, “is it worth it”, price tiers, resale and brand-versus-brand.

Before: a renderer of its own

The site used to draw its slides itself, with HTML slide builders and their own stylesheets rendered in a headless browser (Playwright). That meant a second carousel look to maintain next to ppl.studio's, a browser to launch for every post, and fixes made twice.

The switch

ppl.studio already had a deck engine: the code that draws the slides for its TikTok carousel preset and its other carousels. We exposed it as a command that takes slide words and pictures and returns finished JPEGs, with no database, account or API key involved. advent.center's build script now maps each of its nine formats onto the engine's existing layouts (cover, item, figures, list, pair) and keeps a checkout of ppl.studio that it updates before each draw.

The rule for the move was to reuse layouts, not add new ones. Only four small additions went into the engine (a heading and cards on the doors layout, a line under figures, a doors list without a picture, and a plain-slides input).

Checked side by side first

Before switching, we drew the same three carousels both ways (an Yves Rocher 2026 “inside” carousel, a launched-this-week carousel and a Red Bull 2026 carousel) and compared them slide by slide. ppl.studio's engine was worse on six details, such as product names cut too early and contents value missing from a chip. Those were fixed in the engine before the switch. Afterwards the engine was equal or better on every slide; it also fixed a repeated brand name the old renderer printed (“Red Bull Red Bull Energy Drink”).

What changed

• One carousel engine to maintain. The site's HTML slide builders, stylesheets, font files and its Playwright dependency were deleted; its build script went from 1,624 to 1,250 lines, and all nine formats re-rendered identically after the clean-up.
• No browser per post. A carousel draws in about three seconds.
• Look changes happen once. A fix to ppl.studio's slides reaches advent.center's next draw.

What the carousels reached

A better renderer doesn't make an audience by itself. In the first three weeks on the engine, advent.center posted 140 carousels to four platforms: 84,841 views on TikTok, a median of 5 to 25 views a post on Instagram, Facebook and Pinterest, and TikTok days that were either about 800 views a post or about 16. The numbers, platform by platform and format by format, are in advent.center on social.