Building wetria: from a studio idea to a paid SaaS

wetria is a SaaS that takes a presentation and returns it designed and still editable. We designed and built it ourselves, and it now has paying customers. This is the engineering side of that story: what the product needed, how we built it and what surprised us.

What the product had to do

• Accept a .pptx or PDF up to 120 MB, with fonts, spreadsheets, references and a brand template.
• Run a job for about a minute a slide on the server, so the user can close the tab and get an email.
• Return files that open correctly in PowerPoint, Keynote, Google Slides and Figma.
• Check every slide against the original before the user sees it.
• Charge fairly for very different jobs, and stop a run before it goes past the balance.

The stack

The same stack we use for client products: Next.js and TypeScript, Supabase on PostgreSQL, Stripe for billing and Cloudflare in front. The design and language work runs on Anthropic's Claude models; Google's Gemini scores decks; spoken briefs are transcribed with Deepgram. Every job runs in a sandbox as its own system user, so it sees only its own files.

Billing that matches the work

A ten-slide tidy-up and a thirty-slide redesign cost very different amounts to run. So wetria prices in tokens per slide and per service, sells plans and packs through Stripe subscriptions, supports promo codes, and shows the exact cost on every result. A new account starts with 100 free tokens, and usage limits and abuse control are moderated in the studio's own platform, WeTrio Hub.

What we did not expect: fonts

The hardest problems were not AI. They were fonts. Rendering a PowerPoint file on a server substitutes any font it does not have, and a substitute that is a few percent wider moves every line break on the slide. In our render workers the same phrases came out 13 to 16% wider with the wrong substitute. The fix was to install metric-compatible twins, fonts with exactly the same widths, such as Carlito for Calibri and Caladea for Cambria, and to ship decks with the right fonts for each app. Keynote ignores embedded fonts; Google Slides swaps unknown ones for Arial; Figma drops tables. Each export handles its app.

A check before every result

Generated slides can silently lose a line or a figure. So every slide is compared with the original before the user sees it, and every file is repaired and validated before the check and before every download. It costs time on every run and it is the reason we trust the output enough to sell it.

What it shows about how we build

• The people who designed the screens wrote the pipeline, so the product and the interface did not drift apart.
• The product is monitored, fixed and extended every week after launch.