Writing 2 min read
Introducing: contacts and notifications
Money between two people only works if both sides agree. How Money Diary links contacts by invite, and what it tells you when a loan or split changes.
Zain Haroon — Full-stack Engineer
A loan has two sides, and a tracker that only knows yours is a diary entry with extra steps. Once you can point at a person rather than a name you typed, the same 5,000 can sit in both ledgers and agree with itself.
That is what contacts are for in Money Diary, and notifications are how the other side finds out.
Adding a contact
A contact is a person you exchange money with: a display name, optionally an email. That alone is enough to record loans and splits against them, and to ask who still owes you what.
If you add their email and they use Money Diary, you can send an invite to link the two accounts. Until they accept, the contact is just your own label. Nothing lands in their ledger because you typed their address, which is the property that makes the feature safe to use with real people.
What happens once you are linked
A linked contact turns a one-sided record into a shared one. Record a loan and they get an offer to accept. Mark a repayment and they see the claim. If you edit or delete the loan afterwards, they are told that too, because a ledger that silently changes under someone is worse than no ledger.
Each of those is a notification with its own kind:
- a contact invite, and the response to it
- a loan offer, and the response to it
- a repayment, and a claim that a repayment happened
- a loan changed or deleted after the fact
- a borrow claim, when someone records that you lent to them
Notifications arrive live over a websocket, so the other side does not have to refresh to find out you settled up.
Why acceptance matters
Every one of those flows waits on the other person. An offer is an offer until accepted; a repayment claim is a claim until confirmed. The alternative — letting one person write into another person’s records — is how you end up with two friends and three versions of the truth.
It also means you can use contacts for people who are not on Money Diary at all. Their side just never exists, and yours works exactly as it did before.
Where this shows up
Mostly in lending and splitting: receivables that stay out of your spending totals, and a list of who has not paid you back. Contacts are what put a real person at the other end of those rows.