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

# Introduction

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

## Quick Links

* [Order Flow](/order-flow/api.md) — bundle and private transaction submission
* [Bundle Tracing](/bundle-tracing/api.md) — track bundle lifecycle and inclusion
* [Intra-Block Loans](/intra-block-loans-on-request/api.md) — flash loan protocol for within-block capital access (available on request)
* [Builder Execution Extension](/builder-execution-extension/api.md) — off-chain compute with on-chain execution in a single block
* [End of Block](/end-of-block/api.md) — end-of-block transaction positioning
* [Deterministic Block Placement](/deterministic-block-placement-on-request/api.md) — control where transactions land in a block (available on request)
* [Builder Execution Oracle](/builder-execution-oracle-on-request/api.md) — builder-side data and computation for BEX (available on request)
* [propAMM](/propamm/api.md) — stream your quote updates, and the builder puts them directly ahead of the trades that use your price (market makers, on request)

Start with the [BEX quick start](/builder-execution-extension/quick-start.md) or [coding agent setup](/builder-execution-extension/agent-setup.md).

## 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 two 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>:<signature>
```

The signature is an EIP-191 `personal_sign` over the string `"0x" + hex(keccak256(body))`, where `body` is the exact request body bytes you send. This is the Flashbots signing format. Do not sign the raw body itself.

{% tabs %}
{% tab title="Python" %}

```python
import json
from eth_account import Account
from eth_account.messages import encode_defunct
from eth_utils import keccak

message = json.dumps(body)
account = Account.from_key(private_key)
signature = account.sign_message(encode_defunct(text="0x" + keccak(text=message).hex()))
header_value = f"{account.address}:{signature.signature.hex()}"
```

{% endtab %}

{% tab title="JavaScript" %}

```javascript
const { Wallet, id } = require("ethers"); // ethers v6

const message = JSON.stringify(body);
const wallet = new Wallet(privateKey);
const signature = await wallet.signMessage(id(message));
const headerValue = `${wallet.address}:${signature}`;
```

{% endtab %}
{% endtabs %}

Send `message` as the request body unchanged, since the signature covers those exact bytes.

If the header is missing, you will receive:

```json
{"code": -32001, "message": "method <name> not available: missing signature", "data": {"method": "<name>"}}
```

If the signature does not recover to the address in the header, you will receive:

```json
{"code": -32001, "message": "signature verification failed: signing address mismatch"}
```

If your address is not in the allowlist, 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](/order-flow/api.md)                                            | Open                                                |
| [Bundle Tracing](/bundle-tracing/api.md)                                    | Open                                                |
| [Builder Execution Extension](/builder-execution-extension/api.md)          | Restricted, except `bex_capabilities` which is open |
| [End of Block](/end-of-block/api.md)                                        | Restricted                                          |
| [Deterministic Placement](/deterministic-block-placement-on-request/api.md) | Available on request                                |
| [Intra-Block Loans](/intra-block-loans-on-request/api.md)                   | Available on request                                |

## Coinbase Address

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