RPC overview

Base exposes one EVM-compatible JSON-RPC API across two performance tiers. Switch a single endpoint URL and the pending block tag to move from 2-second sealed blocks to 200ms pre-confirmations — every other method behaves the same.

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

Note

The public endpoints above are rate-limited and not suitable for production traffic. Connect through a node provider for production workloads.

The Flashblocks tier

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

• On Standard endpoints, pending reflects the transaction pool (unmined state).
• On Flashblocks endpoints, pending reflects the pre-confirmed block currently being built, refreshed every ~200ms with new batches of sequencer-ordered transactions.

Methods such as eth_getBalance, eth_getStorageAt, and eth_call execute against real sequencer state up to 1.8 seconds before a block seals, with sub-second latency.

Namespaces

Base nodes implement the standard Ethereum namespaces plus a small set of Base-specific methods.

• eth — core Ethereum protocol methods for accounts, blocks, transactions, gas, and logs. Available on both Standard and Flashblocks endpoints.
• net — network identification (net_version).
• web3 — client identification (web3_clientVersion).
• debug — replay and tracing utilities for deep transaction inspection. Computationally expensive; availability depends on the node provider.
• txpool — inspection of the local mempool.
• base — Base-specific helpers, including pre-confirmation status checks (base_transactionStatus).
• Flashblocks — pre-confirmation methods (eth_simulateV1) and WebSocket streams (newFlashblockTransactions, pendingLogs, newFlashblocks) available only on Flashblocks endpoints.

Method index

Ethereum JSON-RPC API

Methods marked with a check mark support the "pending" block tag on Flashblocks endpoints.

Method	Description	Flashblocks pending
eth_blockNumber	Current block number	—
eth_getBalance	Account ETH balance	yes
eth_getTransactionCount	Account nonce / tx count	yes
eth_getCode	Deployed contract bytecode	yes
eth_getStorageAt	Contract storage slot value	yes
eth_call	Execute read-only call	yes
eth_getBlockByNumber	Block data by number	yes
eth_getBlockByHash	Block data by hash	—
eth_getBlockReceipts	All receipts for a block	yes
eth_getBlockTransactionCountByNumber	Tx count by block number	yes
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	yes
eth_getLogs	Query event logs by filter	yes
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)	yes
eth_unsubscribe	Cancel a subscription (WSS)	—

Flashblocks API

Pre-confirmation methods that deliver sub-second transaction signals on Base. These are only available on Flashblocks endpoints and let you read state, simulate bundles, and stream events up to ~1.8 seconds ahead of block sealing.

Method	Description
eth_simulateV1	Simulate transaction bundles against pre-confirmed state
base_transactionStatus	Check whether 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 the full Flashblock payload stream

Debug API

Development and debugging utilities for transaction replay and block inspection. Debug methods replay execution 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 every transaction in a block by hash
debug_traceBlockByNumber	EVM traces for every transaction in a block by number

Request and 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