Real AI agent use cases, with sources and setup prompts

Build a farmers' market seasonality poster site in one long Claude session

Vertumnus makes printable posters of when each produce variety is in season. It was coded in a single 731-prompt Claude Opus session over 22 days, and the author published the full transcript.

$4 in / $20 out per 1M tokens22 daysIntermediateSource linked

Source

perspectivezoom on Hacker News · 2026-09-08 · Project link

Written in our own words. Credit to the original author. Link checked 2026-10-16.

What they did

Vertumnus makes printable posters of when each produce variety is in season. It was coded in a single 731-prompt Claude Opus session over 22 days, and the author published the full transcript.

Result (as claimed)

Live at vertumnus.fyi with the transcript; 47 points on Show HN.

Tools they used

Claude Opus 5.5

Cost: Claude Opus 5.5: from $4 in / $20 out per 1M tokens.

Set it up

  1. Write a one-page brief

    Describe the app in plain words: who it is for, the 3 core screens or actions, and what "done" looks like.

  2. Start the project with your agent

    Open Claude Opus 5.5 and paste the brief. Ask it to propose a stack and a file plan before writing code.

  3. Build one slice at a time

    Ship the smallest working flow first, run it, then add features one by one. Commit after each working step.

  4. Test it like a user

    Click through on desktop and phone. Ask the agent to add basic tests and fix anything that breaks.

  5. Check security and ship

    Keep keys in environment variables, check auth and database rules, then deploy and share the link.

Copy the full setup prompt

Paste into your agent and it will walk you through the setup, asking before anything that sends, posts or spends.

You are helping me set up this AI use case end to end in Claude Code.

Goal: Build a farmers' market seasonality poster site in one long Claude session
What the original author did: Vertumnus makes printable posters of when each produce variety is in season. It was coded in a single 731-prompt Claude Opus session over 22 days, and the author published the full transcript.
Reported result (as claimed by the author): Live at vertumnus.fyi with the transcript; 47 points on Show HN.
Source: https://news.ycombinator.com/item?id=49604581
Tools they used: Claude Opus 5.5
Category: Vibe coding & apps

Please:
1. Ask me 3 short questions about my situation (accounts I have, budget, what I want the output to look like).
2. Propose a step-by-step plan using these tools or cheaper alternatives, with the time and cost of each step. Use official pricing pages; say "check pricing" if unsure.
3. Then do the setup with me one step at a time, waiting for my OK before anything that sends messages, posts publicly, spends money or deletes data.
4. Finish with a checklist to run it again next time.

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