Solvers

How solvers submit transactions and bundles through Blink's Ethereum auction, including cancellation and builder-compatible API access.

Solvers are a class of originator on Blink — they submit transactions through the standard Ethereum RPC endpoint but receive specialised auction treatment. Specifically:

• Solver transactions are forwarded to builders without a gas recovery delay

• Solver transactions are eligible for a dedicated OFA fan-out window: Blink holds the transaction until 10 seconds into the pending slot, then fans it out to other originators only if no searcher has placed a bid. This preserves searcher exclusivity while still ensuring coverage.

There are two integration paths available to solvers:

Path	Best for
Raw transaction via RPC endpoint	Submitting individual solver transactions
Builder endpoint (/builder/v1/)	Submitting and cancelling bundles using Flashbots-compatible API

---

Cancelling a Transaction

Solvers can cancel a pending transaction by submitting a cancel signal — a zero-value self-transfer with the same nonce as the transaction to cancel.

A cancel transaction is defined as:

• to — same address as the sender

• value — 0

• data — empty

When Blink receives this, it:

1. Detects it is a cancel signal (not a real transaction)

2. Looks up the original transaction by (sender, nonce) in cache

3. Removes the original transaction from the auction

4. Forwards eth_cancelBundle requests to all active builders for the next 3 blocks

The cancel signal itself is never forwarded to builders or stored — only the resulting cancellation is propagated.

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Builder Endpoint

Blink exposes a builder-compatible API at /builder/v1/<originatorId> that emulates the standard Flashbots builder interface. This lets solvers use the same bundle submission code they already use with direct-builder integrations.

The endpoint supports the following JSON-RPC methods:

• eth_sendRawTransaction

• eth_sendBundle

• eth_cancelBundle

eth_sendBundle

Submit a bundle targeting a specific block. Blink fans the bundle out to all active builders.

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "eth_sendBundle",
  "params": [
    {
      "txs": [
        "0x...",
        "0x..."
      ],
      "blockNumber": "0x1488DCF",
      "replacementUuid": "d9be8dba-6954-47bf-8ee2-dab3feeb11ee",
      "revertingTxHashes": []
    }
  ]
}

Field	Type	Required	Description
txs	string[]	Yes	Array of signed raw transactions (hex-encoded)
blockNumber	string	No	Target block number (hex). Defaults to current block
replacementUuid	string	No	Canonical UUID string (RFC 4122); used to cancel or replace this bundle (not an arbitrary opaque string)
revertingTxHashes	string[]	No	Hashes of transactions in the bundle that are allowed to revert
maxTimestamp	number	No	Latest Unix timestamp at which the bundle is valid

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "bundleHash": "0x..."
  }
}

Set ?solver=true as a query parameter to enable solver-mode fan-out for bundles submitted through this endpoint.

eth_cancelBundle

Cancel a previously submitted bundle by its replacementUuid. Blink removes the bundle from its cache and forwards the cancellation to all active builders.

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "eth_cancelBundle",
  "params": [
    {
      "replacementUuid": "d9be8dba-6954-47bf-8ee2-dab3feeb11ee"
    }
  ]
}

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": 200
}

replacementUuid must match exactly what was set in the original eth_sendBundle call. If no matching bundle is found in cache, the cancellation is still forwarded to builders but has no effect on Blink's internal state.