Exchange programmes and home swaps trade whole lives for weeks, and need visas, flights and a spare room. Pen-pal and language apps trade words. Routine Swap trades only the shape of one ordinary day: you wake when they wake, eat what they eat (adapted to your kitchen), walk where they would walk, from wherever you already are. It takes 24 hours, no travel and no address, and you come back with the diary of someone else's life lived in your own body.
The data it runs on
Routines the users write: each person types or speaks their real day as 6 to 12 steps (time, what, a detail). That is the only content source.
Time zones: the IANA time zone database (built into every browser and server through the Intl API) converts each step between cities, including places with daylight saving.
Kitchen and surroundings: what the follower says they have (a tick list of ingredients and "is there water, a park, a market nearby"), never a location.
Limits and gaps: people write vague steps ("work"), routines include work tasks that cannot transfer (baking for customers, nursing patients), and some steps are unsafe in another place (a dark walk at 05:15).
Fallback: a library of sample routines written with consenting volunteers (like Jun's here) so anyone can try a swap on day one without a match. Vague steps are expanded by asking the writer one question.
1. The mission
Let anyone live one day of a stranger's life on the other side of the world, and come back a little less of a stranger to it. One day, step by step, then a shared diary.
2. Why people can't resist it
Novelty without travel. A new day, a new rhythm, a new breakfast, from your own home.
Reciprocity. Someone in Busan is waking at your time and cooking your food today. You do not want to let them down.
Collecting. Each swap is a passport stamp. Bakers, nurses, fishers, tram drivers, from 40 countries.
3. How it works for real
Write: a routine form plus optional voice input (Whisper or Gemini Flash audio for speech to text).
Privacy pass: a fast cheap model (Gemini Flash or DeepSeek via OpenRouter) plus rules flag street names, workplaces, school names and phone numbers, and suggests a vaguer phrase.
Match: pairs people with different time zones and different lives but overlapping hours, from verified accounts only.
Adapt: a frontier LLM (Claude or GPT) rewrites each step for the follower: same clock time, food adapted to their kitchen list, walks adapted to what is near them, work blocks turned into "work in their rhythm", and unsafe steps softened. Every change carries a one-line reason.
Live: step reminders by push; check-ins with a photo (location metadata stripped on device, then a vision model checks for faces of others, house numbers and plates) and a note.
Diary: both sides are merged into a paired diary; the LLM drafts a one-line takeaway each person can edit.
4. Cost per use
Pennies per swap: the adaptation is one LLM call (about $0.01), privacy checks and photo moderation are fractions of a cent each, and the diary draft is one more small call. No video, no maps.
Free: one swap a month and the sample library. Passport ($3 a month): weekly swaps, themed swaps (night shift, farm day, fasting day), printed passport book at year end. Schools buy classroom swaps with partner schools.
5. Growth loop
Every finished swap ends with a postcard share ("I lived a baker's day in Busan from Port Harcourt"). People ask "who would I swap with?" and join to find out. Each new user also adds a new routine to the library.
6. Risks and guardrails
No addresses, ever: routines and notes are scanned for street names, building numbers and workplaces; photos have GPS data removed before upload.
Verified accounts: ID plus selfie check through a verification provider before a first swap; adults only.
No meeting, no money: in-app messages only, no phone numbers, no payment requests; a report button on every message.
Safety over fidelity: no step that is dangerous where you are (walking alone in the dark, fasting with a medical condition, driving); either person can end the swap at any time.
7. MVP build order
Routine form with privacy flags.
Sample library of 10 real routines (with consent) so single-player swaps work on day one.
Claude adaptation prompt: time zone, kitchen list and safety rules in, adapted steps with reasons out.
Swap day screen with step reminders and check-ins.
Paired diary and postcard share; then matching between real users.