# 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.