# Introduction

Eureka Builder is an Ethereum block builder designed for advanced block-level strategies. It provides deterministic transaction placement, intra-block liquidity, bundle lifecycle tracing, and builder-side compute primitives, allowing protocols and searchers to execute strategies directly during block construction.

## Quick Links

* [Order Flow](https://docs.eurekalabs.xyz/order-flow/api) — bundle and private transaction submission
* [Bundle Tracing](https://docs.eurekalabs.xyz/bundle-tracing/api) — track bundle lifecycle, refunds, and block composition
* [Intra-Block Loans](https://docs.eurekalabs.xyz/intra-block-loans/api) — flash loan protocol for within-block capital access
* [Builder Execution Extension](https://docs.eurekalabs.xyz/builder-execution-extension/api) — off-chain compute with on-chain execution in a single block
* [End of Block](https://docs.eurekalabs.xyz/end-of-block/api) — guaranteed end-of-block transaction positioning
* [Deterministic Block Placement](https://docs.eurekalabs.xyz/deterministic-block-placement/api) — control where transactions land in a block
* [Builder Execution Oracle](https://docs.eurekalabs.xyz/builder-execution-oracle/api) — trustless access to builder-side state and computation

## RPC Endpoint

```
https://rpc.eurekabuilder.xyz
```

## Endpoint Access Control

Eureka Builder uses a per-method allowlist to control access to RPC endpoints. Each endpoint falls into one of three categories:

| Access level   | Meaning                  | Signature required? |
| -------------- | ------------------------ | ------------------- |
| **Open**       | Anyone can call          | No                  |
| **Restricted** | Only whitelisted signers | Yes                 |

Restricted endpoints require the `X-Flashbots-Signature` HTTP header:

```
X-Flashbots-Signature: <public_address>:<EIP-191 signature of the request body>
```

If your address is not in the allowlist, or the header is missing, you will receive:

```json
{"code": -32001, "message": "method <name> access rejected. If you need access to this endpoint, contact us at t.me/EurekaBuilder", "data": {"method": "<name>"}}
```

Contact the Eureka team to get your signing address added to the allowlist.

### Access by feature

| Feature                                                                                    | Access     |
| ------------------------------------------------------------------------------------------ | ---------- |
| [Order Flow](https://docs.eurekalabs.xyz/order-flow/api)                                   | Open       |
| [Bundle Tracing](https://docs.eurekalabs.xyz/bundle-tracing/api)                           | Open       |
| [Builder Execution Extension](https://docs.eurekalabs.xyz/builder-execution-extension/api) | Restricted |
| [End of Block](https://docs.eurekalabs.xyz/end-of-block/api)                               | Restricted |
| [Deterministic Placement](https://docs.eurekalabs.xyz/deterministic-block-placement/api)   | Restricted |

## Coinbase Address

**Address:** [eurekabuilder.eth](https://etherscan.io/address/0xfb74767c1ce1aada0a0e114441173b57f8c1571b) \[0xfb74767c1ce1aada0a0e114441173b57f8c1571b]