Base RPC Overview

Complete reference for all JSON-RPC and Flashblocks methods available on Base nodes.

Base exposes a single, fully EVM-compatible JSON-RPC API across two performance tiers. You can move from 2-second block confirmations to 200ms pre-confirmations by switching one URL and one block tag.

Networks

Network	Chain ID	Type	Archive
Mainnet	8453	Production	Yes
Sepolia	84532	Testnet	Yes

Endpoints

Mainnet

Tier	HTTP	WSS
Standard	https://mainnet.base.org	wss://mainnet.base.org
Flashblocks	https://mainnet-preconf.base.org	wss://mainnet-preconf.base.org

Sepolia

Tier	HTTP	WSS
Standard	https://sepolia.base.org	wss://sepolia.base.org
Flashblocks	https://sepolia-preconf.base.org	wss://sepolia-preconf.base.org

The public endpoints above are rate-limited and not suitable for production traffic. For production use, connect through a node provider.

What is the Flashblocks Tier?

Flashblocks endpoints are fully EVM-equivalent; every standard eth_ method works identically. The difference is in what the pending block tag returns:

• On Standard endpoints, pending reflects the transaction pool (unmined state).
• On Flashblocks endpoints, pending reflects the current pre-confirmed block in progress, updated every ~200ms with new batches of sequencer-ordered transactions.

Calls like eth_getBalance, eth_getStorageAt, and eth_call run against real sequencer state up to 1.8 seconds before the block seals, with sub-second latency.

API Reference

Ethereum JSON-RPC API

Core Ethereum protocol methods for account queries, block and transaction data, gas estimation, and log filtering. All methods work on both Standard and Flashblocks endpoints.

Methods marked ✓ support the "pending" block tag on Flashblocks endpoints.

Method	Description	Flashblocks pending
eth_blockNumber	Current block number	—
eth_getBalance	Account ETH balance	✓
eth_getTransactionCount	Account nonce / tx count	✓
eth_getCode	Deployed contract bytecode	✓
eth_getStorageAt	Contract storage slot value	✓
eth_call	Execute read-only call	✓
eth_getBlockByNumber	Block data by number	✓
eth_getBlockByHash	Block data by hash	—
eth_getBlockReceipts	All receipts for a block	✓
eth_getBlockTransactionCountByNumber	Tx count by block number	✓
eth_getBlockTransactionCountByHash	Tx count by block hash	—
eth_getTransactionByHash	Transaction data by hash	—
eth_getTransactionByBlockHashAndIndex	Tx by block hash and index	—
eth_getTransactionByBlockNumberAndIndex	Tx by block number and index	—
eth_getTransactionReceipt	Receipt for a mined tx	—
eth_sendRawTransaction	Submit signed transaction	—
eth_gasPrice	Current gas price	—
eth_maxPriorityFeePerGas	Max priority fee estimate	—
eth_feeHistory	Historical base fee and rewards	—
eth_estimateGas	Estimate gas for a tx	✓
eth_getLogs	Query event logs by filter	✓
eth_chainId	Network chain ID	—
eth_syncing	Node sync status	—
net_version	Network version ID	—
web3_clientVersion	Client version string	—
eth_subscribe	Subscribe to events (WSS)	✓
eth_unsubscribe	Cancel a subscription (WSS)	—

Flashblocks API

Pre-confirmation methods for sub-second transaction signals on Base. These methods are only available on Flashblocks endpoints and enable reading state, simulating bundles, and streaming events up to ~1.8 seconds before a block seals.

Method	Description
eth_simulateV1	Simulate transaction bundles against pre-confirmed state
base_transactionStatus	Check if a transaction has been received by the mempool
newFlashblockTransactions	Subscribe to individual pre-confirmed transactions
pendingLogs	Subscribe to filtered logs from pre-confirmed transactions
newFlashblocks	Subscribe to full Flashblock payload stream

Debug API

Development and debugging utilities for deep transaction inspection and block replay. Debug methods replay transactions and are computationally expensive — availability and rate limits vary by node provider.

Method	Description
debug_traceTransaction	Full EVM execution trace for a transaction
debug_traceBlockByHash	EVM traces for all transactions in a block by hash
debug_traceBlockByNumber	EVM traces for all transactions in a block by number

Request & Response Format

All requests are HTTP POST with Content-Type: application/json.

Field	Type	Description
jsonrpc	string	Always "2.0"
method	string	The RPC method name
params	array	Method parameters in order
id	number | string	Identifier echoed back in the response

Request:

{
  "jsonrpc": "2.0",
  "method": "eth_getBalance",
  "params": ["0x742d35Cc6634C0532925a3b8D4C9dD0b4f3BaEa", "pending"],
  "id": 1
}

Success response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x1a055690d9db80000"
}

Error response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32602,
    "message": "Invalid params"
  }
}

Error Codes

Code	Name	Description
-32700	Parse error	Invalid JSON
-32600	Invalid request	Not a valid JSON-RPC 2.0 object
-32601	Method not found	Method does not exist or is unavailable
-32602	Invalid params	Invalid method parameters
-32603	Internal error	Internal JSON-RPC error
-32000	Server error	Node-specific error (see message)

Block Parameters

Value	Standard	Flashblocks
"latest"	Most recently sealed block	Most recently sealed block
"pending"	Unmined transaction pool state	Current Flashblock in progress (~200ms resolution)
"safe"	Latest safe block	Latest safe block
"finalized"	Latest finalized block	Latest finalized block
"earliest"	Genesis block	Genesis block
"0x<n>"	Specific block by number	Specific block by number

Rollup Node API

The rollup node exposes one additional RPC method not part of the standard Ethereum JSON-RPC API. It is used internally by the fault proof system to retrieve L2 output roots.

optimism_outputAtBlock

Returns an output root and associated metadata for a given L2 block number. The output root is a 32-byte commitment used by the fault proof proposer to anchor disputed L2 state on L1.

Parameters

Name	Type	Description
blockNumber	QUANTITY, 64 bits	L2 integer block number

Returns

Name	Type	Description
version	DATA, 32 Bytes	Output root version number, beginning with 0
outputRoot	DATA, 32 Bytes	The output root
blockRef	Object	L2 block reference — hash, number, parentHash, timestamp, l1origin, sequenceNumber
withdrawalStorageRoot	DATA, 32 Bytes	Storage root of the L2ToL1MessagePasser contract
stateRoot	DATA, 32 Bytes	The state root
syncStatus	Object	Snapshot of the rollup driver sync state across L1 and L2 heads