# What is Solva

The problem Solva solves for fiat tokens and customer money on Stellar, and what Solva is.

## The problem
An anchor issues a fiat-backed token on Stellar, such as USDC, EURC or ARST. A custodial app, such as a wallet or an exchange, holds customer money on Stellar. In both cases, people hold a claim on money that sits in reserve accounts they cannot see.

Holders and partners want to know that the reserves cover what is owed to customers. That answer usually comes from an audit or an attestation, a few times a year. Between those reports, nobody outside the institution can see if the reserves still cover what is owed.

An institution cannot publish every customer balance to prove its total, because that would expose its customers to anyone who looks.

## What Solva is
Solva is an open reserve-coverage registry on Stellar.

**Reserves** are the money an institution holds to back what it owes. **What is owed** is the total of every customer balance. **Reserve coverage**, or **coverage**, means the reserves are at least what is owed. As a formula, `R >= L`, where R is reserves and L is what is owed.

Each cycle, an institution publishes a **zero-knowledge proof** that its reserves cover what it owes. Solva is designed to publish every day. A zero-knowledge proof is a short piece of data that shows a statement is true. In Solva, no balance is a public input to the proof, so the record shows the total is covered and reveals no customer balance. See [Privacy](/docs/overview/privacy).

Each institution has its own **registry**, a contract on Stellar that checks the proof and keeps the result as a **record**. Partners, auditors and other contracts read the record. Any holder can check that their own balance was counted.

| Question             | Answer                                                                               |
| -------------------- | ------------------------------------------------------------------------------------ |
| Who publishes        | Anchors and custodial apps, each to its own registry on Stellar                      |
| What is published    | The reserves total, the total owed, a commitment to the customer list, and the proof |
| What stays private   | Every customer balance and every customer identity                                   |
| Who checks the proof | A contract on Stellar, not Solva                                                     |
| Who reads the record | Anyone: holders, wallets, exchanges, lenders, auditors and contracts                 |

Solva runs on Stellar Testnet today, and on Mainnet <ComingSoon />.

<Callout type="info">
  Solva adds regular evidence between audits, and the audit stays in place. See [Coverage and
  audits](/docs/overview/coverage-and-audits).
</Callout>

## Next
<Cards>
  <Card title="What Solva does" href="/docs/overview/what-solva-does">
    The record, the inclusion check and the reads partners make.
  </Card>

  <Card title="How Solva works" href="/docs/overview/how-solva-works">
    From a reserve balance to a record on Stellar, in plain steps.
  </Card>

  <Card title="Who Solva is for" href="/docs/overview/who-solva-is-for">
    Anchors, custodial apps, their partners and their holders.
  </Card>

  <Card title="Why it matters" href="/docs/overview/why-it-matters">
    Evidence between audits, with customer privacy kept.
  </Card>
</Cards>