Ethereum Mempool (Preview)

Preview. Live as of 2026-08-21. The Ethereum sibling of the Bitcoin mempool: same protocol, ETH transactions.

A live view of the Ethereum public mempool, ingested straight off the eth devp2p wire network (not a single node's eth_subscribe). You sit among many peers and often see a transaction (including a SUBFROST depositAndBridge) before it is mined, and before any one RPC provider's pool surfaces it.

POST https://mainnet.subfrost.io/v4/YOUR_API_KEY/ethereum/mempool       # JSON-RPC
GET  wss://mainnet.subfrost.io/v4/YOUR_API_KEY/ethereum/mempool/ws       # change stream

Both /v4 and /v5 work. This is a public-mempool view: direct-to-builder / private orderflow (Flashbots, exclusive builder RPCs) never propagates over devp2p, so it structurally misses some gas. That is fine for deposit-tracking, not a substitute for a builder feed.

The record

Every transaction is summarised as a TxRecord. The full calldata is fetched on demand, not held resident: you get its length and 4-byte selector.

field	type	notes
hash	0x…32	transaction hash
from	0x…20	recovered signer
to	0x…20 | null	null for contract creation
nonce	number
value	string	wei (decimal string, may exceed 2⁵³)
gas_limit	number
max_fee_per_gas	string	wei
max_priority_fee_per_gas	string	wei
tx_type	number	0 legacy, 2 EIP-1559, 3 blob, …
input_len	number	calldata length in bytes
selector	0x…4	first 4 calldata bytes ("" if none)
first_seen_ms	number	unix ms we first saw it
seq	number	monotonic per-instance sequence

JSON-RPC

JSON-RPC 2.0. params is an OBJECT, not a positional array (a positional array returns -32602).

curl -s https://mainnet.subfrost.io/v4/YOUR_API_KEY/ethereum/mempool \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"mempool_info","params":{}}'

method	params	returns
mempool_info	{}	{count, added_total, removed_total, subscribers, seq}
mempool_txids	{limit}	{txids:[0x…], count, seq}
mempool_entry	{txid}	the TxRecord, or -32000 if not resident
mempool_recent	{limit}	{entries:[TxRecord], seq}, newest first

error	meaning
-32601	unknown method
-32602	invalid params (e.g. positional array)
-32000	not found: the txid is not in the mempool

WebSocket change stream

Connect to …/ethereum/mempool/ws. Text frames, one JSON object each; every frame carries seq so you can detect gaps.

→  {"op":"subscribe","channels":["tx","block"]}
←  {"type":"hello","instance":"a3f1c07e","seq":40213}
←  {"type":"add","record":{ …TxRecord… },"seq":40214}
←  {"type":"remove","hash":"0x…","reason":"mined","seq":40219}
←  {"type":"block","number":21234567,"hash":"0x…","removed":41,"seq":40260}

• Client ops: subscribe / unsubscribe (channels: "tx", "block") and ping.
• Server frames: hello (first), add (a TxRecord), remove{hash,reason}, block{number,hash,removed}, reset{reason,action:"resync"}, pong.
• Backpressure: a client too slow to drain falls off the broadcast ring and receives reset{action:"resync"}; the server never buffers on its heap. On a reset, re-fetch state with mempool_recent and resume from the new seq.

Tracking a crosschain deposit

To surface "Deposit pending on Ethereum" the moment a user's bridge tx hits the mempool, subscribe to tx and match add frames whose:

• to == the frUSD vault 0x95779e7e1c943042255b8a78273fe6de4823cf06, and
• selector == 0xbedb65ee (depositAndBridge).

That fires before the transaction is mined; the confirmed on-chain record then appears in the frUSD Deposits index once it lands.

Caveats

• Public mempool only: misses private/builder orderflow (see above).
• Preview: the shape is stable but the service is young; treat gaps as possible and lean on seq + reset to resync rather than assuming a perfect stream.