> For the complete documentation index, see [llms.txt](https://docs.syndromics.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.syndromics.xyz/protocol/overview.md).

# Protocol overview

Syndromics is a marketplace, not a pool. There is no shared pot of USDG and no interest-rate curve. Instead, three kinds of participants interact through one settlement contract and a public order book of signed messages.

## Actors

| Actor        | What they do                                                                                                                                                      | How they are gated                                             |
| ------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------- |
| **Borrower** | Holds Stock Tokens, creates borrow requests, submits settlements, repays, tops up, refinances.                                                                    | `BORROWER` role in the eligibility registry                    |
| **Lender**   | Signs offers (targeted or standing), receives position NFTs, is repaid pro rata, can opt in to idle-capital parking and in-kind liquidation.                      | `LENDER_PROFESSIONAL` today, `LENDER_RETAIL` where permitted   |
| **Keeper**   | Triggers liquidation auctions, accepts refinance bids on behalf of lenders, sends margin alerts, rebalances idle capital. Earns a share of liquidation penalties. | `LIQUIDATOR` role to receive collateral; otherwise open        |
| **Relayer**  | Stores and serves signed offers, validates them against chain state, suggests matches. Anyone can run one.                                                        | `RELAYER` role only where a relayer submits on behalf of users |

## Objects

* **Market**: a tuple `(collateralToken, loanToken, oracle, ltvConfig)`. Markets are isolated. A Stock Token can exist in several markets with different loan assets or parameters, and a failure in one market cannot spread to another.
* **Borrow request**: the borrower's intent, held by the relayer and referenced by targeted offers.
* **Offer**: an EIP-712 message. See [Offers and matching](/protocol/offers-and-matching.md).
* **Loan**: the on-chain record created at settlement. One loan has one borrower, one collateral escrow and one or more slices.
* **Slice**: one lender's share, represented by a position NFT. See [Syndication](/protocol/syndication.md).

## The core loop

```mermaid
flowchart LR
  B[Borrower] -->|1. borrow request| R[(Relayer order book)]
  L[Lenders] -->|2. signed offers| R
  R -->|3. matched set| B
  B -->|4. settle request, offers, sigs| S[LoanSettlement]
  S -->|check| E[EligibilityRegistry]
  S -->|price| O[OracleRouter]
  S -->|escrow| C[(Collateral)]
  S -->|pull USDG| L
  S -->|principal| B
  S -->|mint| P[Position NFTs]
  B -->|5. repay or refinance| S
  K[Keeper] -->|6. HF below 1.0| A[LiquidationAuction]
```

1. A borrower posts a request: collateral token and amount, principal, maximum APR, term (7, 14, 30 or 90 days), fill deadline.
2. Lenders sign offers off-chain. Offers can target that request or stand against a token or tier.
3. The borrower (or a keeper on their behalf) collects a matching set from the relayer.
4. One `settle` transaction verifies signatures and eligibility, checks LTV against the oracle with session haircuts, escrows collateral, pulls USDG from each lender and mints one position NFT per slice.
5. Interest accrues per second at each slice's fixed APR. The borrower repays any time after the minimum interest period, or opens a refinance auction before maturity.
6. If collateral value falls so that the health factor drops below 1.0, anyone may start a Dutch auction of the collateral. Lenders are paid first; any surplus returns to the borrower.

Every step above is an on-chain event. The only off-chain component is the order book of unsettled signed offers, which is public and mirrored by the indexer.

## What the protocol never does

* It never holds lender funds before a match.
* It never lends against anything without a live oracle price (negotiated Tier D loans on the roadmap are the deliberate, professional-only exception, with no automatic liquidation).
* It never socialises losses.
* It never pauses repayment or post-repayment collateral withdrawal.

## Related pages

* [Loan lifecycle](/protocol/loan-lifecycle.md) for the state machine.
* [Health factor and liquidation](/protocol/health-and-liquidation.md) for the risk mechanics.
* [Smart contracts](/architecture/smart-contracts.md) for the on-chain components.


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