docs: add UniswapX revert reasons reference page

docs/contracts/uniswapx/05-revert-reasons.md

@@ -0,0 +1,81 @@
+---
+id: revert-reasons
+title: Revert Reasons
+sidebar_position: 5
+---
+
+UniswapX reactors revert with typed Solidity errors, which can be difficult to decode from a raw transaction receipt. Before submitting a fill transaction, fillers should use the `OrderQuoter` contract (or the UniswapX SDK wrapper) to simulate the fill and decode the revert reason — this avoids wasted gas and helps attribute failures to the right party.
+
+## Order Validation States
+
+The `OrderValidation` enum in the SDK captures every meaningful validation outcome. The table below describes each state and who is responsible for resolving it.
+
+| State | Meaning | Who's Responsible |
+|---|---|---|
+| `OK` | Order is valid and fillable. | — |
+| `Expired` | Order deadline has passed. | Filler (timing) |
+| `NonceUsed` | Order nonce already consumed — order was filled or cancelled. | Protocol / Filler |
+| `InsufficientFunds` | Swapper wallet lacks sufficient token balance or approval. | Swapper (surface to user) |
+| `InvalidSignature` | Order signature is invalid or doesn't match the swapper. | Protocol |
+| `InvalidOrderFields` | One or more order fields are malformed (bad decay times, amounts, reactor address, etc.). | Protocol / Filler |
+| `ValidationFailed` | External validation contract rejected the order (often exclusivity). | Filler |
+| `ExclusivityPeriod` | Order is in its exclusivity window and the caller is not the exclusive filler. | Filler (timing / routing) |
+| `OrderNotFillableYet` | Order's start time hasn't been reached (Priority orders). | Filler (timing) |
+| `InvalidGasPrice` | Gas price doesn't meet the order's requirements (Priority orders). | Filler |
+| `InvalidCosignature` | Cosigner signature is missing or invalid (Cosigned orders). | Protocol / Filler |
+| `UnknownError` | Unrecognized revert — check raw revert data. | — |
+
+## Error Selector Reference
+
+The table below maps 4-byte error selectors to their corresponding `OrderValidation` state. Use this as a lookup when decoding raw revert data from the reactor.
+
+| Selector | State | Source |
+|---|---|---|
+| `8baa579f` | `InvalidSignature` | — |
+| `815e1d64` | `InvalidSignature` | — |
+| `756688fe` | `NonceUsed` | — |
+| `302e5b7c` | `InvalidOrderFields` | Invalid dutch decay time |
+| `773a6187` | `InvalidOrderFields` | Invalid dutch decay time |
+| `4ddf4a64` | `InvalidOrderFields` | Invalid reactor address |
+| `d303758b` | `InvalidOrderFields` | Both input and output decay |
+| `7c1f8113` | `InvalidOrderFields` | Incorrect amounts |
+| `43133453` | `InvalidOrderFields` | Invalid dutch decay time |
+| `48fee69c` | `InvalidOrderFields` | — |
+| `70f65caa` | `Expired` | — |
+| `ee3b3d4b` | `NonceUsed` | — |
+| `0a0b0d79` | `ValidationFailed` / `ExclusivityPeriod` | Exclusive filler check — maps to `ExclusivityPeriod` when `additionalValidationData` encodes an exclusive filler |
+| `b9ec1e96` | `ExclusivityPeriod` | — |
+| `062dec56` | `ExclusivityPeriod` | — |
+| `75c1bb14` | `ExclusivityPeriod` | — |
+| `a305df82` | `InvalidOrderFields` | Invalid cosigner output |
+| `ac9143e7` | `InvalidOrderFields` | Invalid cosigner input |
+| `fff08303` | `InvalidOrderFields` | Duplicate fee output |
+| `d7815be1` | `InvalidCosignature` | `InvalidCosignature()` |
+| `TRANSFER_FROM_FAILED` | `InsufficientFunds` | ERC-20 transfer failure |
+| `d856fc5a` | `InvalidOrderFields` | Invalid fee escalation amounts |
+| `cd21db4f` | `Expired` | Signature expired |
+| `769d11e4` | `Expired` | `PriorityOrderReactor: InvalidDeadline()` |
+| `c6035520` | `OrderNotFillableYet` | `PriorityOrderReactor: OrderNotFillable()` |
+| `a6b844f5` | `InvalidOrderFields` | `PriorityOrderReactor: InputOutputScaling()` |
+| `f3eb44e5` | `InvalidGasPrice` | `PriorityOrderReactor: InvalidGasPrice()` |
+
+## Using the SDK to Pre-flight Orders
+
+The UniswapX SDK's `OrderQuoter` class wraps the on-chain quoter contract and decodes the revert reason into the `OrderValidation` enum. Call it before sending your fill transaction to avoid wasted gas:
+
+```typescript
+import { OrderQuoter, OrderValidation } from '@uniswap/uniswapx-sdk';
+
+const quoter = new OrderQuoter(provider, chainId);
+const { validation } = await quoter.validate({ order, signature });
+
+if (validation !== OrderValidation.OK) {
+  console.error('Order invalid:', OrderValidation[validation]);
+}
+```
+
+Running this simulation before submission lets you skip unwinnable fills, surface `InsufficientFunds` errors to your UI, and distinguish timing issues (e.g. `ExclusivityPeriod`) from permanent failures (e.g. `InvalidSignature`).
+
+---
+
+For broader context on building a fill bot — including order polling, execution flow, and webhook registration — see the [Filler Integration Guide](/contracts/uniswapx/fillers/filleroverview).

docs/contracts/uniswapx/fillers/filleroverview.md

@@ -106,7 +106,7 @@ Fillers should start with polling for orders and rate limit at 6rps. If after po
 <details>
   <summary>The transaction is reverting for a certain reason (e.g. `InvalidOrderFields`). What does this mean?</summary>
 
-    Check the [KNOWN_ERRORS](https://github.com/Uniswap/sdks/blob/a7fb8d7b8eecdc8a29d386420339da86b0361a77/sdks/uniswapx-sdk/src/utils/OrderQuoter.ts#L70) in the SDK to see what the likely causes are.
+    Check the [Revert Reasons](/contracts/uniswapx/revert-reasons) reference page to see what the likely causes are.
 
 </details>