Reference — Hood Synapse

A

Connect

wallet · sdk

Network parameters

Robinhood Chain is an Arbitrum Orbit L2 settling to Ethereum. It is EVM-equivalent, so existing tooling — ethers, viem, web3.py, Foundry — works unchanged.

MAINNET

chainId4663 · 0x1237

rpcrpc.mainnet.chain.robinhood.com

explorerrobinhoodchain.blockscout.com

TESTNET

chainId46630 · 0xB626

rpcrpc.testnet.chain.robinhood.com

faucetfaucet.testnet.chain.robinhood.com

ADD TO WALLETjavascript

await window.ethereum.request({
  method: 'wallet_addEthereumChain',
  params: [{
    chainId: '0x1237',
    chainName: 'Robinhood Chain',
    nativeCurrency: {
      name: 'Ether', symbol: 'ETH', decimals: 18
    },
    rpcUrls: ['https://rpc.mainnet.chain.robinhood.com'],
    blockExplorerUrls: ['https://robinhoodchain.blockscout.com']
  }]
});

Request envelope

Every call is an HTTP POST with the same JSON body. Only method and params change between calls.

No API key, no account, no headers beyond content type.

Everything returns hex. Heights, balances, gas and timestamps are hex strings. Decode with parseInt(h,16), or BigInt(h) when the value can exceed 2⁵³.

REQUESTcurl

curl -X POST https://rpc.mainnet.chain.robinhood.com \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber",
       "params":[],"id":1}'

RESPONSEjson

{ "jsonrpc": "2.0", "id": 1, "result": "0xdec54d" }

B

Chain state

identity · gas

eth_chainIdVERIFIED

Network identifier. Use it to refuse work when a wallet is pointed at the wrong chain.

PARAMS

none—

RESPONSEjson

{ "result": "0x1237" }   // 4663

eth_gasPriceVERIFIED

Current gas price in wei. On this chain it sits around 0.05 gwei — roughly three orders of magnitude below Ethereum L1.

RESPONSEjson

{ "result": "0x30e9f90" }   // 0.0514 gwei

eth_maxPriorityFeePerGasVERIFIED

Returns 0x0.

Tipping buys nothing here. Ordering is decided by the sequencer, not by a fee auction. Set priority fee to zero and let the base fee carry the transaction.

RESPONSEjson

{ "result": "0x0" }

web3_clientVersionVERIFIED

Node build string. Confirms the chain runs Arbitrum Nitro, which is what makes the Orbit fields further down appear.

RESPONSEjson

{ "result": "nitro/v3.11.3-rc.4-4bed0c5/linux-arm64/go1.25.12" }

C

Blocks

~4s cadence

eth_getBlockByNumberVERIFIED

Fetch a block by height, or by the tag latest.

PARAMS

blockhex height or 'latest'

fulltrue expands transactions into objects

Passing false returns hashes only and is much lighter — use it for polling.

RESPONSE (trimmed)json

{
  "number":        "0xdec54d",
  "timestamp":     "0x6a5dec90",
  "gasUsed":       "0x71d02",
  "baseFeePerGas": "0x3165ff0",
  "transactions":  [ /* 6 hashes */ ],
  // orbit-only, see section E
  "l1BlockNumber": "0x1863755",
  "sendRoot":      "0xf6c227e8…",
  "sendCount":     "0x227"
}

Polling for new blocks

The public endpoint is HTTP only — no WebSocket subscriptions. New blocks are discovered by polling.

Poll at block time. Blocks land every ~4s. Polling every second triples your request count and hands you the same block three times.

POLLERjavascript

let seen = 0;

setInterval(async () => {
  const b = await call('eth_getBlockByNumber', ['latest', false]);
  const h = parseInt(b.number, 16);
  if (h === seen) return;
  seen = h;
  console.log(h, b.transactions.length, 'tx');
}, 4000);

D

Accounts

balances · code

eth_getBalanceVERIFIED

Balance in wei at a given block.

PARAMS

address20-byte hex

block'latest' or hex height

Use BigInt. Wei values overflow JavaScript's safe integer range. Convert with BigInt(hex) and only cast to Number after dividing by 1e18.

CALLjavascript

const wei = await call('eth_getBalance', [addr, 'latest']);
const eth = Number(BigInt(wei)) / 1e18;
// 0.000237

eth_getCode

Returns deployed bytecode. An empty result (0x) means the address is a plain wallet, not a contract — the cheapest way to tell them apart.

RESPONSEjson

{ "result": "0x" }        // EOA, not a contract

E

Transactions

submitted vs executed

eth_getTransactionByHash VERIFIED

eth_getTransactionReceipt VERIFIED

A transaction has two halves and you need both: what was submitted (the transaction) and what happened (the receipt).

Mined is not successful. A reverted transaction still occupies a block and still burns gas. Check receipt.status === '0x1' before treating anything as done.

CAPTURED FROM MAINNETpython

h  = '0xb951c0274bd58288b01dbf3a94965a7efdfed4c2…'
tx = call('eth_getTransactionByHash', [h])
rc = call('eth_getTransactionReceipt', [h])

# from   0x6d9da725…  →  to  0x24d7cd0d…
# status 0x1  (success)
# gas    189,966
# logs   5

System transactions

Most blocks open with an internal ArbOS transaction: sender equals recipient, value is zero, gasUsed is 0x0.

It is chain bookkeeping, not user activity.

Filter it out. Counting raw transactions.length inflates every metric you publish by one per block.

SYSTEM TX SHAPEjson

{
  "from":    "0x…000a4b05",
  "to":      "0x…000a4b05",   // identical
  "value":   "0x0",
  "gasUsed": "0x0"
}

F

Events

logs · filters

eth_getLogs

Historical events, filtered by address and topic.

Always bound the range. With ~4s blocks, 2,000 blocks ≈ two hours of history — page through longer windows in chunks rather than widening one query until it times out.

FILTERjavascript

const latest = parseInt(await call('eth_blockNumber'), 16);

const logs = await call('eth_getLogs', [{
  fromBlock: '0x' + (latest - 2000).toString(16),
  toBlock:   'latest',
  address:   contract,
  topics:    [transferTopic]
}]);

G

Orbit internals

not on ethereum

l1BlockNumber

The Ethereum L1 block this L2 block is anchored to. An L2 block is only as final as the L1 block behind it — read this when you need real finality, not just inclusion.

FIELDjson

"l1BlockNumber": "0x1863755"   // 25,573,205

sendRoot · sendCount

Messages travelling L2 → L1 (withdrawals, cross-chain calls) accumulate into a merkle tree. sendRoot is its current root; sendCount is the running total of queued messages.

Watch sendCount to detect outbound activity without parsing every transaction.

FIELDSjson

"sendRoot":  "0xf6c227e8bd780bce1fd394c5bcd9513f…",
"sendCount": "0x227"                // 551

The miner field is the sequencer

There is no mining and no validator here. The miner address is a readable marker — decode its tail as ASCII and it spells what it is.

DECODEjavascript

const m = '0xa4b000000000000000000073657175656e636572';
Buffer.from(m.slice(-18), 'hex').toString();
// → "sequencer"

H

Known gaps

handle these

eth_syncingUNAVAILABLE

Not exposed on the public endpoint. Clients that assume it exists will read undefined and carry on silently.

Check for error first. A JSON-RPC failure returns HTTP 200 with an error object — inspect it before touching result.

RESPONSEjson

{
  "error": {
    "message": "the method eth_syncing does not exist/is not available"
  }
}

I

Limits

going to production

The public endpoint

Free, keyless, CORS-open — ideal for reading, prototyping and browser apps. It is rate limited and not intended for production.

Move to a dedicated provider once you need archive history, throughput, or an uptime guarantee: Alchemy, QuickNode, Blockdaemon, dRPC, Validation Cloud.

Never sign in the browser. Everything documented here is read-only. Private keys belong in a wallet the user controls or a backend you control — never in page code.

ENDPOINT PROPERTIESsummary

auth          none — no key required
cors          access-control-allow-origin: *
transport     HTTP POST only — no websocket
rate limit    yes, unspecified — back off on failure
archive       not guaranteed

Robinhood Chain reference.

Connect

Chain state

Blocks

Accounts

Transactions

Events

Orbit internals

Known gaps

Limits