# MEV-Boost Block Payment Lookup via Flashbots Relay

> MEV-Boost Block Payment Lookup via Flashbots Relay is a paid API for AI agents from agent402.tools, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-13).

Looks up the MEV-Boost payment details for a specific Ethereum beacon chain slot or execution layer block number via the Flashbots relay, returning builder, proposer, ETH value paid, gas usage, and transaction count.

## Facts

- Endpoint: POST https://agent402.tools/api/mev-block-payment
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/mev-boost-block-payment-lookup-via-flashbots-relay-f3aa3a22
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_11qBIPu1rONG4YUvaQjbk

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability mev-boost-block-payment-lookup-via-flashbots-relay-f3aa3a22 -d '<json body>'
```

Example prompt: What was the MEV-Boost payment for Ethereum slot 8900000? I want to know who the builder and proposer were, how much ETH was paid, and the gas usage.

## When to prefer this

Use this endpoint when you need to investigate MEV-Boost payment data for a specific Ethereum block or beacon chain slot and want Flashbots relay-specific data including builder/proposer identities, ETH value, and gas metrics. Prefer this over on-chain explorers when you need structured, machine-readable MEV relay data without parsing raw blockchain transactions.

## Known failure modes

- found=false returned when block was built locally or via a non-Flashbots relay
- Neither slot nor blockNumber provided — API requires at least one
- Invalid slot or block number format causing a 400 error
- Block too recent and not yet indexed by the Flashbots relay
- Flashbots relay temporarily unavailable causing timeout or 5xx error

## How this service works

Look up the MEV-Boost payment for a specific slot or block number via the Flashbots relay. Returns the builder, proposer, value paid in ETH, gas usage, and tx count. Returns found=false if the block was built locally or via a different MEV-Boost relay (Flashbots is one of several).

## Output

Returns a JSON object with: found (boolean indicating if the block was relayed via Flashbots), builder address, proposer address, ETH value paid to the proposer, gas used, gas limit, and transaction count. Returns found=false if the block was built locally or via a different MEV-Boost relay.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "slot": {
   "type": "number",
   "description": "Beacon chain slot number (one of slot/blockNumber required)."
  },
  "blockNumber": {
   "type": "number",
   "description": "Execution layer block number (one of slot/blockNumber required)."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "slot": 12345678,
  "found": true,
  "numTx": 187,
  "relay": "flashbots",
  "gasUsed": 14987654,
  "gasLimit": 30000000,
  "valueEth": 0.072345,
  "valueWei": "72345000000000000",
  "blockHash": "0xabc...",
  "blockNumber": 22000000,
  "builderShort": "0x90000000…abcdef",
  "builderPubkey": "0x9000...",
  "proposerPubkey": "0xa000...",
  "proposerFeeRecipient": "0x1234..."
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/mev-boost-block-payment-lookup-via-flashbots-relay-f3aa3a22/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent402.tools](https://www.zero.xyz/host/agent402.tools/llms.txt)