Mempool
List unconfirmed transactions and mempool size for a chain.
# Mempool
`GET https://api.rarebl.com/open/tx/mempool` or `POST https://api.rarebl.com/open/tx/mempool`
Unconfirmed transactions the node currently sees, newest first, with the mempool size.
**Rate class:** read (5 requests per second, burst 20, per IP). **Available since:** Open API v1.
## Request
Send the parameters as query parameters (GET) or as a JSON object (POST with `Content-Type: application/json`). They are identical either way. No API key is needed: `X-API-KEY` is reserved and ignored.
Example: `curl "https://api.rarebl.com/open/tx/mempool?chain=btc&limit=2"`
## Parameters
| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `chain` | string | Yes | The chain to query. One of: btc, ltc, bch, dash, eth, tron. |
| `limit` | integer | No | Transactions to return. 1 to 100 Default 25. |
## Responses
### API200 (HTTP 200): OK
Mempool size and a sample of pending transactions.
```json
{
"status": 1,
"code": "API200",
"message": "success",
"data": {
"count": 68328,
"bytes": 24527873,
"items": [
{
"hash": "313da871f52272bbf0fa799af9d46dca0efbc329570dff0a4e30e6dd3f4eb6d4",
"block": null,
"time": null,
"status": "pending",
"from": null,
"to": "bc1qanfrvw5lunlemvm09dthnxmwknal0fw0q7jfnm",
"value": "0.000363",
"fee": null,
"method": null,
"inputs": 1,
"outputs": 2,
"firstSeen": "2026-11-14T22:23:08Z"
},
{
"hash": "cf106e2e83ff9f7ac23bef28795db36132c14cde7e0b1c3c070c9378598d6a8d",
"block": null,
"time": null,
"status": "pending",
"from": null,
"to": "bc1p8ah4ltyv9w2z00ynvulgwxjv8z78mgr5lectl7ey7kacahx8ltrs37wlvd",
"value": "0.00195024",
"fee": null,
"method": null,
"inputs": 3,
"outputs": 6,
"firstSeen": "2026-11-14T22:23:08Z"
}
]
},
"go": null,
"meta": {
"requestid": "0123456789abcdef",
"notices": []
}
}
```
| Field | Type | Description |
| --- | --- | --- |
| `data.count` | integer \| null | Transactions in the mempool. |
| `data.bytes` | integer \| null | Mempool size in bytes. |
| `data.items[]` | TxSummary | Pending transactions, newest first. Each has `firstSeen` (ISO 8601 UTC): when the backend first saw it. |
### API400 (HTTP 400): Bad Request
A parameter is missing or malformed. `data.param` names it (here `chain`).
```json
{
"status": 0,
"code": "API400",
"message": "Unknown or missing chain.",
"data": {
"param": "chain"
},
"go": null,
"meta": {
"requestid": "0123456789abcdef",
"notices": []
}
}
```
### API409 (HTTP 409): Conflict
The node has no pending-transaction view for that chain right now (for example ETH while its node has no pending block).
```json
{
"status": 0,
"code": "API409",
"message": "This node has no pending transaction view.",
"data": {
"reason": "no_mempool_view"
},
"go": null,
"meta": {
"requestid": "0123456789abcdef",
"notices": []
}
}
```
### API429 (HTTP 429): Too Many Requests
Rate limited (5 requests per second per IP, burst 20). A `Retry-After` header says how long to wait, in seconds.
```json
{
"status": 0,
"code": "API429",
"message": "Too many requests. Please retry shortly.",
"data": null,
"go": null,
"meta": {
"requestid": "0123456789abcdef",
"notices": []
}
}
```
### API502 (HTTP 502): Bad Gateway
The node is unavailable, still syncing or timed out. Retry later with a short back-off.
```json
{
"status": 0,
"code": "API502",
"message": "The node is unavailable or timed out. Please try again.",
"data": null,
"go": null,
"meta": {
"requestid": "0123456789abcdef",
"notices": []
}
}
```
## Notes
- UTXO chains return a sample from the node's mempool, not a complete list: the Bitcoin mempool holds tens of thousands of transactions. `count` is the real size.
- On pending UTXO items `fee` and `from` are null. TRON returns at most 50 transactions from the node's pending list.
- The reply is cached for about 3 seconds and shared between callers.