> ## Documentation Index > Fetch the complete documentation index at: https://cobo.com/products/agentic-wallet/manual/llms.txt > Use this file to discover all available pages before exploring further. # Transactions and gas > How on-chain transactions work and what gas fees are. ## What is a transaction A **transaction** is a signed message submitted to a blockchain that changes its state — transferring tokens, calling a contract function, or deploying a new contract. Once included in a block, transactions are permanent and irreversible. When you inspect an EVM transaction on a block explorer, its recorded parameters show everything that single submission includes: | Field | Description | | ---------------------- | ---------------------------------------------------------------------------------- | | `from` | The account initiating and paying gas | | `to` | The recipient address or contract | | `value` | Amount of native token to send (zero for most contract calls) | | `data` | Encoded function call for contracts; empty for plain transfers | | `gas limit` | Maximum computation the sender is willing to pay for | | `maxFeePerGas` | Maximum total gas price the sender is willing to pay (EIP-1559) | | `maxPriorityFeePerGas` | Tip paid to the block producer to prioritize inclusion (EIP-1559) | | `nonce` | A sequential counter that prevents the same transaction from being submitted twice | > Most modern EVM transactions use the EIP-1559 fee format. Legacy transactions with a single `gasPrice` field are still valid but less common. ### Transaction hash Every submitted transaction receives a unique **transaction hash** (tx hash) — a hex string like `0x4a3f8b2c...`. This is how you look up a transaction on a block explorer: | Chain | Block explorer | | ----------------- | ---------------------------------------------------------- | | Ethereum mainnet | [etherscan.io](https://etherscan.io) | | Ethereum Sepolia | [sepolia.etherscan.io](https://sepolia.etherscan.io) | | Base mainnet | [basescan.org](https://basescan.org) | | Base Sepolia | [sepolia.basescan.org](https://sepolia.basescan.org) | | Polygon PoS | [polygonscan.com](https://polygonscan.com) | | Arbitrum One | [arbiscan.io](https://arbiscan.io) | | Optimism | [optimistic.etherscan.io](https://optimistic.etherscan.io) | | BNB Smart Chain | [bscscan.com](https://bscscan.com) | | Avalanche C-Chain | [snowtrace.io](https://snowtrace.io) | | Solana mainnet | [solscan.io](https://solscan.io) | Cobo returns the transaction hash after successful submission. ### Gas fees On-chain transactions require a fee to compensate the network for computation and storage. The fee model differs between EVM chains and Solana. #### EVM chains Gas is the unit of computational work. Every operation costs a fixed amount of gas, and the total fee depends on how much computation the transaction requires: ``` Transaction fee (EVM) = gas used × gas price (in Gwei) ``` Gas is paid in the chain's native token — ETH on Ethereum and Base, POL on Polygon, BNB on BNB Smart Chain, AVAX on Avalanche. Modern EVM transactions use the EIP-1559 fee model, which splits the gas price into two components: | Component | Field | Description | | ------------ | ---------------------- | ------------------------------------------------------ | | Base fee | — | Set by the protocol; burned, not paid to validators | | Priority fee | `maxPriorityFeePerGas` | Tip paid to the block producer to prioritize inclusion | The `maxFeePerGas` field caps the total amount the sender is willing to pay. Any difference between `maxFeePerGas` and the actual base fee + priority fee is refunded. Gas prices fluctuate with network congestion. During high activity, fees can spike significantly. #### Solana Solana uses a different fee model with two components: | Component | Description | | ------------ | ---------------------------------------------------------------------------------- | | Base fee | A flat fee per signature, charged in lamports (1 SOL = 1,000,000,000 lamports) | | Priority fee | An optional fee per compute unit to increase processing priority during congestion | ``` Transaction fee (Solana) = (number of signatures × base fee per signature) + (compute units × compute unit price) ``` Solana transactions also carry a recent blockhash that expires after approximately 150 blocks (\~1 minute). If a transaction is not included within that window, it becomes invalid and must be resubmitted. Agents that submit transactions autonomously should account for this expiry when retrying. ## Transaction lifecycle in Cobo Agentic Wallet This lifecycle is specific to Cobo Agentic Wallet. Other products and platforms may handle transaction submission and signing differently. ``` Submit → Policy validation → MPC signing → Broadcast → Included in block → Confirmed ``` 1. **Policy validation** — the policy engine (governed by the pact) checks the transaction. If it violates a policy, it is blocked before reaching the network. 2. **MPC signing** — if it passes, the transaction is co-signed: the agent and Cobo for agent-initiated transactions; the app and Cobo for app-initiated transactions. 3. **Broadcast** — the signed transaction is sent to the network, included in a block, and confirmed. ## Transaction finality TTransactions are not final the moment they are submitted. They must be included in a block and confirmed by subsequent blocks. For high-value operations, waiting for additional confirmations beyond the first provides stronger settlement guarantees. | Chain | Time to first confirmation | Practical finality | | ---------------- | -------------------------- | ----------------------- | | Ethereum mainnet | \~12 seconds | \~3 minutes (15 blocks) | | Base mainnet | \~2 seconds | \~10 seconds | | Polygon PoS | \~2 seconds | \~10 seconds | | Solana mainnet | \~400 milliseconds | \~2 seconds | | Ethereum Sepolia | \~12 seconds | \~3 minutes | | Base Sepolia | \~2 seconds | \~10 seconds | Cobo waits for block inclusion before marking a transaction as confirmed.