Mempool JSON-RPC

Preview. Live as of 2026-08-11. See the overview for the data model.

POST https://mainnet.subfrost.io/v4/{api_key}/mempool

JSON-RPC 2.0. Single requests and arrays (batches) are both accepted.

params is an OBJECT, not a positional array. This differs from the esplora_* and metashrew_* families on the same host. A positional array returns -32602.

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

Errors

HTTP-level: 401 INVALID_API_KEY, 403 when admin is required, 503 AUTH_UNAVAILABLE when the key store cannot be consulted.

503 AUTH_UNAVAILABLE is a refusal, not an outage to retry through. This service authenticates itself rather than relying on an upstream gate, and it fails closed — if it cannot check your key it serves nobody.

---

mempool_info

No params. The cheap poll.

{
  "count": 142331, "bytes": 78412992, "vbytes": 41203118,
  "total_fee": 812340000, "fee_known": 141002, "fee_coverage": 0.9906,
  "provisional": 3, "seq": 918273, "instance": "a3f1c07e",
  "added_total": 4102773, "removed_total": 3960442, "subscribers": 12
}

fee_coverage is 0.0..=1.0. See the overview.

---

mempool_txids

{ "limit": 1000 }

Clamped to 5000.

{ "txids": ["…"], "count": 142331, "seq": 918273 }

Order is unspecified and unstable. It reflects internal slab order, which changes as slots recycle. Sort client-side if you need one; do not treat two consecutive calls as comparable sequences.

---

mempool_entry

{ "txid": "<display-order hex>", "include_hex": false }

{
  "txid": "…", "wtxid": "…",
  "vsize": 141, "weight": 561,
  "fee": 1410, "feerate": 10.0,
  "first_seen": 1754770000123,
  "seq": 918001,
  "origin": "p2p", "provisional": false, "rbf": true
}

first_seen is when we first saw it, not when the node did — the two differ by the arrival latency of whichever source got there first. fee and feerate are absent when unknown.

Returns -32000 when the transaction is not in the mempool.

---

mempool_entries

{ "txids": ["…", "…"], "include_hex": false }

At most 5000 per call.

{ "entries": [ … ], "missing": ["…"] }

Absent txids come back in missing rather than erroring the whole batch.

---

mempool_raw

{ "txid": "…" }

{ "hex": "0100…" }

---

mempool_recent

{ "limit": 100 }

The most recently arrived entries, newest first.

{ "entries": [ … ], "seq": 918273 }

This is the animation seed: paint from this, then follow the WebSocket from the returned seq.

---

mempool_snapshot

{ "limit": 1000, "cursor": 0, "include_hex": false }

{
  "entries": [ … ], "cursor": 917400, "has_more": true,
  "seq": 918273, "count": 142331, "instance": "a3f1c07e"
}

cursor is a sequence number, not an offset. Paging a set that mutates under you by offset skips and repeats entries; paging by seq is stable because a seq is never reused. Pass the returned cursor back for the next page.

Use the returned seq and instance as your WebSocket since_seq to attach without a gap.

---

mempool_feerate_histogram

{ "buckets": [0, 1, 2, 5, 10, 20, 50] }

Bucket floors in sat/vB, ascending. Defaults to a 24-bucket geometric scale.

{
  "histogram": [[0.0, 0], [1.0, 412000], [2.0, 1840221]],
  "fee_coverage": 0.9906,
  "count": 142331
}

Each pair is [bucket_floor_sat_per_vb, vbytes].

Only fee-known entries contribute, so read fee_coverage first. A freshly started service has a thin histogram, and deriving an estimate from it without checking quotes the floor. The transaction still broadcasts, still looks fine, and simply does not confirm.

---

observe (admin only)

POST /v4/{admin_key}/mempool/observe

Not JSON-RPC. Body is {"hex":"0100…"} or the raw transaction bytes.

Requires an api key flagged admin. The transaction enters the store with origin: "edge" and provisional: true.

This does not broadcast. The transaction is not forwarded to bitcoind — the endpoint holds no such capability. It exists so a broadcast made elsewhere shows up in the stream immediately rather than after relay latency. Something else must actually send it.