Searchers — Submit Bundles

A searcher watches the mempool for profitable opportunities (arbitrage, back-runs, liquidations) and packages them into atomic bundles. Submitting those bundles is how searcher order flow reaches a builder.

On Vouch, bundles are submitted to the Vouch Builder — the builder behind builder.vouch.run. It assembles blocks from those bundles and bids through the MEV-Relay.

This is the Vouch Builder — not BlockFerret

Bundle submission goes to the Vouch Builder. BlockFerret is the separate Switch.win × Vouch alliance builder. (Bundle submission to BlockFerret is not currently available.)

How it fits the stack

Endpoint and method

• Endpoint: POST https://builder.vouch.run
• Method: eth_sendBundle (JSON-RPC 2.0) — this is the only method the edge accepts.

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "eth_sendBundle",
  "params": [{
    "txs": ["0x..."],
    "blockNumber": "0x1A2B3C",
    "minTimestamp": 0,
    "maxTimestamp": 0,
    "revertingTxHashes": []
  }]
}

Authentication

Requests are authenticated with the standard Flashbots signature scheme:

• Header: X-Flashbots-Signature: <0x-address>:<0x-signature>
• The signature is over keccak256 of the raw request body, rendered as a 0x-hex string, signed with the EIP-191 personal_sign envelope.
• The recovered address must match the header address and be on the allowlist.

import json, requests
from eth_account import Account
from eth_account.messages import encode_defunct
from web3 import Web3

body = json.dumps(payload, separators=(',', ':'))      # the exact bytes you send
body_hash = Web3.keccak(text=body).hex()               # 0x-hex string
signature = Account.sign_message(
    encode_defunct(text=body_hash), private_key=key
).signature.hex()

requests.post(
    "https://builder.vouch.run",
    data=body,
    headers={
        "Content-Type": "application/json",
        "X-Flashbots-Signature": f"{address}:{signature}",
    },
)

Failed authentication returns a generic 401 — the proxy never reveals which check failed.

Onboarding

Bundle submission is allowlisted:

1. Send your signing address to the Vouch team (see Support).
2. Vouch adds it to the allowlist.
3. Once allowlisted, your signed bundles are accepted immediately.

Bundle fields

Field	Notes
txs	The signed transactions in the bundle.
blockNumber	Required. An absolute target block (0x-hex or decimal). latest, pending, and 0 are rejected.
replacementUuid	Optional. Replaces an earlier bundle targeting the same block.
minTimestamp / maxTimestamp	Optional validity window (0 = no bound).
revertingTxHashes	Optional. Transactions allowed to revert without invalidating the bundle.

Back-run bundles

A bundle may include a currently-pending public transaction (the trigger) as raw signed bytes, followed by your transaction — for example [trigger, back-run]. Both execute in order.

• If the trigger is mined elsewhere first, the bundle fails simulation and is dropped atomically — your back-run cannot land without the trigger.
• Resubmit targeting the new head; the new blockNumber changes the body, so it will not hit the replay guard.
• Include the trigger inside the bundle to guarantee ordering — don't rely on mempool ordering.

Limits

• Rate limit: 30 requests per rolling 2 seconds (~15/s sustained) per IP. Beyond that you get HTTP 429 with Retry-After ≤ 2s. These values are current as of 2026-10 and may change — contact us if you need more headroom.
• There is no hard cap on the number of bundles per block — inclusion is bounded by block gas and by competition with other bundles and mempool transactions.
• Up to 64 transactions per bundle.
• Combined transaction bytes ≤ 192 KiB; request body ≤ 256 KiB.
• 120-second replay window — an exact duplicate body within 120s is rejected (409).
• Only eth_sendBundle is accepted.

PulseChain notes

• The builder credits a bundle with everything it sends to block.coinbase — direct transfers and priority fees both count. Bundles compete with other bundles and mempool transactions on that value.
• Recommended: the standard direct block.coinbase transfer — it is exact and independent of the base fee.
• PulseChain's base fee is high (roughly 500k–700k gwei), so the payment transaction's base-fee burn is ~10–15 PLS. Payments below that will not rank and can be dropped.
• The Vouch Builder sweeps the full coinbase delta to the proposing validator's fee recipient as the block's payment transaction.

Performance and coverage

• The builder and relay run in central Europe (Vienna, Austria). Submit from a host in central Europe for the lowest latency.
• Coverage: roughly 11% of PulseChain blocks are proposed through the Vouch relay — about 927 of ~8,400 blocks/day, with ~5,200 validators registered (~11% of the active set) as of 2026-10-13. Live numbers are on the delivered-blocks explorer.
• HTTP 200 means your bundle was accepted for the target block — it is not a guarantee of inclusion. The bundle must simulate cleanly and win the ordering against other bundles and mempool transactions.

Support

• Telegram