A team-morale app where the team is the weather. Everyone drops one anonymous mood ping a day; the pings aggregate into a living river — calm and sunny through storm and rapids — that every teammate watches change in real time. Each member floats on the river as an avatar whose pose they choose themselves.
Built solo in ~24 hours for the AWS Builder Center Full Stack Challenge (word prompt: CURRENT).
Live app: https://main.d3unb3p2wvfry3.amplifyapp.com
The one-line thesis: Undercurrent shortens the distance between when a team starts struggling and when its lead finds out. It prompts a conversation; it does not replace one.
Anonymity is structural, not promised. A Ping carries a score but no
author; a PingReceipt carries an author but no score. The schema physically
cannot leak what it never stored. One-ping-per-day rides on the receipt's
deterministic id and DynamoDB's conditional writes.
One source of truth for the weather. Clients never compute weather locally.
A Lambda on the Ping table's stream recomputes a single WeatherState row per
team and publishes it through an AppSync mutation — which is what makes every
open browser's river change at once. Below 5 pings, the average never leaves
the server (the "anonymity floor").
React + TypeScript + Vite · AWS Amplify Gen 2 (Cognito, AppSync + DynamoDB, Lambda) · Amazon Bedrock (Claude Haiku 4.5) for the lead's "current report" · Canvas 2D for the river (no game engine, no art assets). One Lambda is deliberately Python 3.12 + boto3.
Architecture, diagrams, and the five load-bearing decisions: docs/architecture.md. The full build log — decisions, dead ends, and fixes as they happened: NOTES.md.
npm install
npx ampx sandbox # deploys a personal cloud backend, writes amplify_outputs.json
npm run dev # http://localhost:5173Five demo accounts share one team (demoN@undercurrent.local, ask for the
password). demo1 is ana, the lead — she sees the report tab and can
take someone off the river from the team tab (they rejoin on their next
sign-in; there's no ban list in a hackathon). demo2–demo5 are kai, mira, theo, and
june. A sixth account, dev@undercurrent.local, is in the dev group and gets
the dev tab: forget today's pings so accounts can ping again, wipe the
river, or wipe-and-reseed a fresh presentable day. Anyone can sign up with a
real email and join the same river.
Everyone picks a pose (floating, waving, on a raft, underwater, struck, coconut mode) and a spot on the river (drifting, the headwater, the rapids, on the big rock, in the shade, the shallows, the eddy). Both are self-chosen and never inferred from mood data; both sync live to every open window.
Visiting? Sign up with any email and you land in simulation mode: six made-up teammates have already pinged, you're the seventh, and your stone decides the weather — nothing you do reaches a real team. The header toggle switches to the live demo team; reset the simulation re-rolls your teammates.
Tabs live in the URL hash (#team, #report, #dev), so refresh, back, and
deep links behave with no router.
All npx tsx scripts/<name>.ts; set OUTPUTS=<path> to target another
backend's amplify_outputs.json (defaults to the local sandbox).
| Script | Env | What it proves / does |
|---|---|---|
prove-realtime.ts |
TEST_EMAIL, TEST_PASSWORD |
ping → stream → Lambda → AppSync mutation → subscription event, pass/fail in 30s |
prove-report.ts |
lead account creds | button-as-a-row → Python Lambda → Bedrock → Report readable by the lead; fails on fallback bodies |
seed-demo.ts |
any member creds | a day of demo pings past the anonymity floor |
seed-members.ts |
DEMO_PASSWORD |
names and poses for the five-member cast |
reset-demo.ts [receipts|all|reseed] |
DEV_EMAIL, DEV_PASSWORD |
the terminal twin of the dev tab |