# Tefi.app

> Corner store credit (el fiado) co-signed on Solana: store and neighbor each sign from their own phone, building a repayment history the neighbor can take anywhere.

Tefi.app is a mobile web app that replaces the paper notebook where corner stores in Argentina write down what they sell on credit ("el fiado"). Every fiado and every repayment is a Solana transaction signed by both the store and the neighbor, each from their own phone. The repayments add up to a history that belongs to the neighbor and that any lender can read on-chain.

How it works:

1. Each phone is set up as the store or as a neighbor and creates only the signing key of that role. There is no sign-up: the key is created on the phone and stays there.
2. The store types the amount in Argentine pesos, takes a photo of the receipt and signs first. The request appears as a QR code.
3. The neighbor scans the QR with their own phone, checks what the transaction says, adds the second signature and sends it to Solana.
4. When the neighbor pays, the store confirms the repayment and the neighbor co-signs it the same way. Each on-time repayment raises the neighbor's on-chain score and credit limit.

Questions and answers:

- **What is el fiado?** In Argentina and across Latin America, corner stores let neighbors take their groceries and pay later, and write the debt down in a paper notebook. That informal credit is called el fiado.
- **Does Tefi.app move real money?** No. It runs on Solana devnet, a test network, and it is a prototype: do not use it for real money. It records the debt and its repayment in USDC units as a stable unit of account; the money itself changes hands between neighbor and store in cash or by transfer, as it does today.
- **Does the neighbor need crypto or SOL?** No. The store pays the network fee of every transaction, including the creation of the neighbor's profile in their first fiado.
- **Can the store or the neighbor record a debt alone?** No. The program only accepts a fiado or a repayment that carries both signatures. The neighbor's phone rebuilds the transaction, verifies the store's signature over it and rejects anything that is not exactly a Tefi fiado or repayment for its own key.
- **Where is the data stored?** Fiados, repayments and scores are accounts of the Tefi program on Solana devnet. Tefi has no server or database of its own: the signing keys and the receipt photos stay on the phones.
- **Is Tefi.app open source?** Yes, under the MIT license. The Anchor program, the web app and the tests are in the GitHub repository.

Facts:

- App: https://tef-iapp.vercel.app/ (English) and https://tef-iapp.vercel.app/es/ (Spanish)
- Network: Solana devnet, a test network. It is a prototype: not for real money.
- Program id: 9UmX9z1Cr2FCidUBgoMJzDCRp5aeTs7xz4umKRnEGnJQ
- Version: 2.1.0 (commit 9f86e7e, 2026-10-11)
- License: MIT

## Docs

- [README](https://github.com/devOr05/tefi-app/blob/main/README.md): the problem, how the two-phone co-signature works, the stack and the devnet transactions that show it
- [Changelog](https://github.com/devOr05/tefi-app/blob/main/CHANGELOG.md): what changed in each version

## Source and on-chain program

- [GitHub repository](https://github.com/devOr05/tefi-app): the Anchor program, the web app and the tests
- [Tefi program on Solana Explorer](https://explorer.solana.com/address/9UmX9z1Cr2FCidUBgoMJzDCRp5aeTs7xz4umKRnEGnJQ?cluster=devnet): the program deployed on devnet

## Optional

- [Versión en español](https://tef-iapp.vercel.app/es/): the same page in Spanish