<!-- source: https://secondlayer.tools/docs/api-reference#list-mempool-transactions -->

## Pending transactions

`GET /v1/index/mempool`

Pending transactions this instance's node has seen since the observer connected, in arrival order. A single-node, go-forward view: the backlog from before the observer connected is never replayed. Confirmed transactions leave the list. No height window. Never cached.

### Filters

| Name | Type | Description |
| --- | --- | --- |
| `sender` | string | Sender principal. Exact match. |
| `type` | string | Transaction type as stored, e.g. `contract_call`, `token_transfer`. Exact match. |
| `contract_id` | string | Called contract. Exact match. |
| `function_name` | string | Called function. Exact match. |

### Range and paging

| Name | Type | Description |
| --- | --- | --- |
| `limit` | integer · 1 to 1000 | Page size; capped at 1000. |
| `cursor` | string | Opaque `next_cursor` from a previous page. Pass it back unchanged. Mutually exclusive with `from_cursor`. |
| `from_cursor` | string | Same as `cursor`. |

### Returns

A cursor envelope; `mempool` holds `MempoolTransaction` objects.

### Responses

- `200` Cursor-paginated envelope
- `400` A parameter, filter, cursor or body field was refused; `code` says which
- `401` This bind requires the instance token, and it was missing or wrong
- `429` Rate limited; retry after `Retry-After` seconds

### Example

```bash
curl https://api.secondlayer.tools/v1/index/mempool \
  -H "Authorization: Bearer $SECONDLAYER_API_KEY"
```

```json
{
  "mempool": [
    {
      "cursor": "bToyNjg4Mjc0",
      "tx_id": "0x00a5cd852c25c5bb5cc7f97c60b88a6a635c001ad431e2133f366be85d5ce0f0",
      "tx_type": "token_transfer",
      "sender": "SM1Z09F6431EQT8GCTEF496TCT5JDTPJ3VFF9Q766",
      "received_at": "2026-09-23T15:11:05.629Z",
      "fee": "1732",
      "nonce": "37",
      "sponsored": false,
      "anchor_mode": "any",
      "post_condition_mode": "deny",
      "post_conditions": [],
      "token_transfer": {
        "recipient": "SMJWA5YRH2DRANX3V96Z6JJSFBE03Z9Y0WHN3XSQ",
        "amount": "79559850769",
        "memo": "572826509"
      }
    }
  ],
  "next_cursor": "bToyNjg4Mjc0",
  "tip": {
    "block_height": 9048690,
    "finalized_height": 9048457,
    "lag_seconds": 4,
    "source_block_height": 9048692
  }
}
```