Base Kolibrio OFA Searcher Connection

Summary: The interface is fully compatible with MEV Blocker. Connect to the WebSocket, include the X-Bev-Signature header, subscribe to partial pending transactions, and receive notifications via JSON-RPC. Construct your backrun bundle from the incoming signals and submit it using eth_sendBundle.

Important behavioral difference vs ETH stream

BASE’s stream not only hides the transaction signature, it also masks the gas fields in the transaction payload (fakes gas-related values). When a searcher wins a bid, they will receive the same transaction notification again — but with the real gas values.

This means you must treat duplicate notifications for the same transaction hash as authoritative updates, and you must update/correct your gas-price estimates for any pending bids based on the later message that contains the real gas info. Failing to do so will cause your bundle bids to be priced incorrectly.

BASE Auction Time: 250ms

Endpoint

wss://bev-relay.kolibr.io/base

Required HTTP header when establishing the WebSocket session:

X-Bev-Signature: <signature>

The X-Bev-Signature header is used for authentication/authorization. The signature format and keys are provided by the Kolibrio team.

Subscription

After a successful connection, send the following JSON‑RPC request to subscribe:

{"method": "eth_subscribe","params": ["mevblocker_partialPendingTransactions"]}

Expected response:

{"jsonrpc": "2.0", "id": 1, "result": "0xd58bbbc0f5190962eff01b6f0ec17724"}

After this, you’ll start receiving eth_subscription notifications when new relevant transactions appear.

Incoming Signal Format

Example notification:

{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "subscription": "0x6e...",
    "result": {
      "hash": "0xb3406...",
      "chainId": "0x2105",
      "type": "0x2",
      "from": "0x192...",
      "to": "0x4...
      "value": "0x5af3107a4000",
      "data": "0xffff",
      "nonce": "0x0",
      "gas": "0x5208",
      "maxPriorityFeePerGas": "0xf4240",
      "maxFeePerGas": "0x26643aa",
      "accessList": []
    },
    "revshareAddress": "0x90000...."
  }
}

Note: The bacrkun bid should be sent to in WETH or ETH to revshareAddress Note: All numeric fields are hex‑encoded.

🧩 Two-Phase Gas Revelation

Kolibrio implements a two-phase gas revelation mechanism to ensure fair bidding behavior across searchers.

When a transaction first appears in the Kolibrio stream, its gas parameters are intentionally masked. Only after a valid bid is submitted - the real gas values be revealed.

This process happens in two distinct phases:

Phase 1 — Initial Signal (Fake Gas)

You’ll receive an early notification containing placeholder (fake) gas values.

Example:

{
  "hash": "0xabc...",
  "maxFeePerGas": "0x5f5e100",  // FAKE (e.g. 100 gwei)
  "maxPriorityFeePerGas": "0x3b9aca00",
  "revshareAddress": "0x90000...."
}

At this stage:

Treat the message as a signal.
Submit your initial bundle using the placeholder gas with WETH or ETH transfer to revshareAddress from signal
Record the transaction hash for later update.

Phase 2 — Real Gas (After Valid Bid)

If your initial bid is valid and wins the action, Kolibrio will resend the same transaction hash. This time, the payload will include the real gas parameters.

Example:

{
  "hash": "0xabc...",
  "maxFeePerGas": "0x26643aa",  // REAL (e.g. 40 gwei)
  "maxPriorityFeePerGas": "0x1dcd6500", 
  "revshareAddress": "0x90000...."
}

At this stage:

Replace the placeholder gas data with the real one.
Resubmit a final bundle with correctly priced gas.

Sending a Bundle

Once you’ve built your signed backrun transaction, send it as a bundle via the same WebSocket or simple HTTP POST request:

{
		"jsonrpc": "2.0",
		"id": 1,
		"method": "eth_sendBundle",
		"params": [
		              {
				"txs": [
				"0x02abcd...", // target transaction hash (32 bytes)
				"0x02abcd..." // your signed bacrkun raw transaction
				...
				]
				}
		]
}

Best Practices & Constraints

Send your bid/payment to the provided revshareAddress
Treat the target transaction hash as a 32‑byte hex string (with 0x prefix).
Both transaction hashes and raw signed transactions are accepted in txs.
The order of txs matters: target transaction first, followed by your backrun txs.

Example Flow

Open WS connection → wss://bev-relay.kolibr.io/base with X-Bev-Signature.
Send eth_subscribe to mevblocker_partialPendingTransactions.
Receive eth_subscription messages with result with fake gas
Process and build your backrun transaction with WETH or ETH transfer to revshareAddress. Send eth_sendBundle containing the target hash and your signed transaction.
In 0-250ms - Receive eth_subscription messages with result with real gas
Process and build your backrun transaction with WETH or ETH transfer to revshareAddress. Send eth_sendBundle containing the target hash and your signed transaction.

Security Notes

Keep your signing keys and X-Bev-Signature secrets secure.

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Last updated 1 day ago