---
title: "Transaction Pool"
description: "Inspect and monitor the Base txpool through RPC extensions and tracing instrumentation."
source: https://basehub.org/integration-guides/txpool/
---
The Base transaction pool holds pending transactions until the builder includes them in a block. The `base/base` repository ships RPC extensions and tracing instrumentation for inspecting pool contents and monitoring transaction lifecycle events.

## Relevant Crates

| Crate | Description |
|-------|-------------|
| `base-txpool-rpc` | Txpool RPC namespace extensions -- provides JSON-RPC methods for querying pool contents. |
| `base-txpool-tracing` | Tracing instrumentation for txpool operations -- emits structured logs and metrics for transaction lifecycle events. |

These crates live under [`crates/execution/`](https://github.com/base/base/tree/main/crates/execution) in the repository.

## How Transactions Flow Through the Pool

```
User / Application
       │
       ▼
┌─────────────────┐
│  JSON-RPC        │   eth_sendRawTransaction
│  (ingress-rpc)   │
└────────┬────────┘
         │
         ▼
┌─────────────────┐
│  Validation      │   Nonce check, balance check, gas price check
│                  │
└────────┬────────┘
         │
         ▼
┌─────────────────┐
│  Transaction     │   Pending pool (ready to include)
│  Pool            │   Queued pool (future nonce gap)
└────────┬────────┘
         │
         ▼
┌─────────────────┐
│  Block Builder   │   Selects transactions for next block/flashblock
│                  │
└─────────────────┘
```

1. **Ingress** -- transactions arrive via `eth_sendRawTransaction` through the ingress RPC.
2. **Validation** -- each transaction is validated: signature verification, nonce ordering, sufficient balance for gas and value, gas price meets the minimum.
3. **Pool insertion** -- valid transactions enter the pool. Transactions with the next expected nonce go into the **pending** sub-pool (ready for inclusion). Transactions with a future nonce go into the **queued** sub-pool (waiting for the gap to be filled).
4. **Promotion** -- when a pending transaction is included in a block or flashblock, queued transactions from the same sender may be promoted to pending if the nonce gap is closed.
5. **Selection** -- the block builder pulls transactions from the pending pool, ordered by effective gas price, for inclusion in the next flashblock delta.

## RPC Methods

The `base-txpool-rpc` crate extends the standard txpool namespace with the following methods.

### `txpool_status`

Returns the number of transactions in each sub-pool.

```bash
curl -X POST https://your-base-rpc-endpoint \
  -H "Content-Type: application/json" \
  -d '{
    "method": "txpool_status",
    "params": [],
    "id": 1,
    "jsonrpc": "2.0"
  }'
```

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "pending": "0x12",
    "queued": "0x3"
  }
}
```

### `txpool_content`

Returns all transactions in the pool, grouped by sender address and nonce.

```bash
curl -X POST https://your-base-rpc-endpoint \
  -H "Content-Type: application/json" \
  -d '{
    "method": "txpool_content",
    "params": [],
    "id": 1,
    "jsonrpc": "2.0"
  }'
```

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "pending": {
      "0xSenderAddress": {
        "0": { "hash": "0x...", "gasPrice": "0x...", "nonce": "0x0", "..." : "..." },
        "1": { "hash": "0x...", "gasPrice": "0x...", "nonce": "0x1", "..." : "..." }
      }
    },
    "queued": {
      "0xAnotherSender": {
        "5": { "hash": "0x...", "gasPrice": "0x...", "nonce": "0x5", "..." : "..." }
      }
    }
  }
}
```

### `txpool_inspect`

Returns a text summary of all transactions in the pool (lighter-weight than `txpool_content`).

```bash
curl -X POST https://your-base-rpc-endpoint \
  -H "Content-Type: application/json" \
  -d '{
    "method": "txpool_inspect",
    "params": [],
    "id": 1,
    "jsonrpc": "2.0"
  }'
```

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "pending": {
      "0xSenderAddress": {
        "0": "0xRecipient: 0 wei + 21000 gas x 1000000000 wei"
      }
    },
    "queued": {}
  }
}
```

### `txpool_contentFrom`

Returns transactions from a specific sender address.

```bash
curl -X POST https://your-base-rpc-endpoint \
  -H "Content-Type: application/json" \
  -d '{
    "method": "txpool_contentFrom",
    "params": ["0xSenderAddress"],
    "id": 1,
    "jsonrpc": "2.0"
  }'
```

```json
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "pending": {
      "0": { "hash": "0x...", "nonce": "0x0", "..." : "..." }
    },
    "queued": {}
  }
}
```

## Tracing and Observability

The `base-txpool-tracing` crate instruments the transaction pool with structured tracing events. When enabled, it emits events for:

| Event | Description |
|-------|-------------|
| `txpool.insert` | A transaction was inserted into the pool. Includes sender, nonce, hash, gas price. |
| `txpool.promote` | A queued transaction was promoted to pending (nonce gap filled). |
| `txpool.discard` | A transaction was removed from the pool (replaced, expired, or invalidated). |
| `txpool.replace` | A transaction was replaced by a new one with the same nonce and higher gas price. |
| `txpool.evict` | A transaction was evicted due to pool size limits. |

These events can be consumed by any `tracing` subscriber -- written to stdout, sent to a logging backend, or exported as OpenTelemetry spans.

### Enabling Tracing

Tracing is configured via the node's logging configuration. For example, to enable debug-level txpool tracing:

```bash
RUST_LOG=base_txpool_tracing=debug base-reth-node \
  --http \
  --http.api eth,txpool
```

## Practical Tips

- **Nonce management** -- use `eth_getTransactionCount` with the `"pending"` tag (see [Flashblocks RPC](/integration-guides/flashblocks-rpc/)) to get the latest nonce including flashblock-preconfirmed transactions. This avoids nonce collisions when submitting transactions rapidly.
- **Gas price monitoring** -- query `txpool_status` periodically to gauge pool congestion. A high pending count relative to block throughput suggests rising base fees.
- **Transaction replacement** -- to speed up or cancel a pending transaction, submit a new transaction with the same nonce and a higher gas price (typically at least 10% higher to be accepted by the pool).
- **Pool limits** -- the pool has configurable size limits. When full, the lowest-priced transactions are evicted first. Monitor `txpool.evict` tracing events to detect when your transactions might be at risk.

## Further Reading

- [Crate Reference](/crates/overview/) -- overview of all crate groups, including the execution crates.
- [Flashblocks RPC](/integration-guides/flashblocks-rpc/) -- using the `"pending"` tag for preconfirmed nonces and balances.
- [Connecting to Base](/integration-guides/connecting/) -- network endpoints and chain parameters.