solana-tx-building Checked

ALTs let you reference accounts by a compact index into an on-chain table rather than including the full 32-byte pubkey. This dramatically increases the number of accounts a transaction can reference.

AddressTableLookup {
    account_key: Pubkey,           // The ALT account address
    writable_indexes: [u8],        // Indices for writable accounts
    readonly_indexes: [u8],        // Indices for read-only accounts
}

**When to use v0**: Any transaction referencing more than ~20 accounts, Jupiter swaps with multi-hop routes, complex DeFi interactions.

Compute Budget

Every transaction has a compute budget that determines how many compute units (CUs) it can consume and what priority fee to pay.

### Compute Budget Instructions

Two key instructions from the Compute Budget Program (ComputeBudget111111111111111111111111111111):

**1. Set Compute Unit Limit**

Instruction data: [0x02, <units as u32 LE>]

Sets the maximum CUs this transaction can consume. Default is 200,000 per instruction (max 1,400,000 per transaction). Setting this lower than needed causes the transaction to fail. Setting it higher wastes budget but does not cost more (you only pay for requested, not consumed).

**2. Set Compute Unit Price**

Instruction data: [0x03, <micro_lamports as u64 LE>]

Sets the price per CU in micro-lamports. This is the priority fee mechanism. The total priority fee is:

priority_fee = compute_unit_limit * compute_unit_price / 1_000_000

### Priority Fee Estimation

To estimate an appropriate priority fee:

1. Call getRecentPrioritizationFees RPC method with the accounts your transaction touches

2. Look at the median or 75th percentile fee from recent slots

3. During congestion, fees spike — monitor and adjust dynamically

import httpx

def get_priority_fees(rpc_url: str, accounts: list[str]) -> list[dict]:
    """Fetch recent prioritization fees for given accounts."""
    resp = httpx.post(rpc_url, json={
        "jsonrpc": "2.0",
        "id": 1,
        "method": "getRecentPrioritizationFees",
        "params": [accounts]
    })
    return resp.json()["result"]

Common Transaction Patterns

### 1. SOL Transfer

The simplest transaction: a System Program transfer.

# System Program transfer instruction data layout:
# [2, 0, 0, 0]  (u32 LE = instruction index 2 = Transfer)
# + amount as u64 LE (lamports)
import struct

def build_sol_transfer_data(lamports: int) -> bytes:
    """Build instruction data for a SOL transfer."""
    return struct.pack("<I", 2) + struct.pack("<Q", lamports)

Accounts required:

1. Sender (signer, writable)

2. Recipient (writable)

### 2. SPL Token Transfer

Transferring SPL tokens requires the Token Program.

# Token Program transfer instruction:
# [3]  (instruction index 3 = Transfer)
# + amount as u64 LE
def build_token_transfer_data(amount: int) -> bytes:
    """Build instruction data for an SPL token transfer."""
    return bytes([3]) + struct.pack("<Q", amount)

Accounts required:

1. Source token account (writable)

2. Destination token account (writable)

3. Owner/delegate (signer)

### 3. Create Associated Token Account (ATA)

Before transferring tokens, the recipient must have an Associated Token Account.

# ATA Program: instruction index 0 = Create
# No instruction data needed (empty bytes)
ATA_PROGRAM_ID = "ATokenGPvbdGVxr1b2hvZbsiqW5xWH25efTNsLJA8knL"

Accounts required (in order):

1. Payer (signer, writable) — pays rent

2. Associated token account (writable) — the ATA to create

3. Wallet address — owner of the new ATA

4. Token mint

5. System Program

6. Token Program

### 4. Jupiter Swap

Jupiter provides a /swap-instructions endpoint that returns pre-built instructions. See the jupiter-api skill for full details.

General flow:

1. Get a quote from /quote

2. Get swap instructions from /swap-instructions

3. Build transaction with setup instructions + swap instruction + cleanup instructions

4. Add compute budget instructions

5. Simulate, then sign and send

Simulation

Always simulate before sending. Use the simulateTransaction RPC method:

def simulate_transaction(rpc_url: str, tx_base64: str) -> dict:
    """Simulate a transaction without submitting it.

    Args:
        rpc_url: Solana RPC endpoint URL.
        tx_base64: Base64-encoded serialized transaction.

    Returns:
        Simulation result with logs and compute units consumed.
    """
    resp = httpx.post(rpc_url, json={
        "jsonrpc": "2.0",
        "id": 1,
        "method": "simulateTransaction",
        "params": [
            tx_base64,
            {"encoding": "base64", "replaceRecentBlockhash": True}
        ]
    })
    result = resp.json()["result"]
    if result["value"]["err"]:
        print(f"Simulation failed: {result['value']['err']}")
        for log in result["value"].get("logs", []):
            print(f"  {log}")
    else:
        cu = result["value"].get("unitsConsumed", 0)
        print(f"Simulation OK — {cu} compute units consumed")
    return result

The replaceRecentBlockhash: True flag lets you simulate even if your blockha