Advanced Cross-Chain Swap Verification: How to Validate Intent-Based Transactions and Detect Malicious Solvers

Cross-chain swaps have become the backbone of decentralized asset movement, and NEAR Protocol’s recent milestone of one million completed swaps through its Intents system confirms that intent-based architecture is winning the infrastructure war. But with scale comes attack surface. As AI agents and automated systems increasingly drive cross-chain transaction volume — and with Bitcoin at $109,232 making every transaction high-value — the ability to independently verify swap execution, detect malicious solver behavior, and recover from failed transactions is no longer optional knowledge. This advanced tutorial provides a technical walkthrough for experienced users who want to move beyond trusting the frontend interface and verify every step of their cross-chain swaps.

The Objective

By the end of this tutorial, you will be able to manually verify that a cross-chain swap executed correctly without relying on the swap provider’s user interface. You will understand how to trace an intent from submission through solver matching to final settlement, identify the on-chain footprints of each step, and detect common manipulation techniques including slippage exploitation, sandwich attacks through solver collusion, and unauthorized token approvals hidden in swap calldata. This knowledge applies to NEAR Intents, but the verification principles are universal across intent-based cross-chain systems.

Prerequisites

This tutorial assumes you are comfortable with basic blockchain concepts including transaction hashes, gas fees, and token approvals. You will need access to block explorers for the chains involved in your swaps — Etherscan for Ethereum, NEAR Explorer for NEAR Protocol, and Solscan for Solana. A basic understanding of ERC-20 token standards and how approval transactions work is essential. You should also have a wallet that exports transaction calldata in hexadecimal format, as we will be decoding swap parameters manually.

Install a calldata decoder tool. The easiest option is the online decoder at 4byte.directory, which maps four-byte function selectors to human-readable function signatures. For more advanced analysis, install Foundry’s cast tool, which can decode arbitrary calldata locally. You will also need the contract addresses for the swap protocols you use — these are available in each protocol’s documentation and should be verified against official sources, not social media posts.

Step-by-Step Walkthrough

Step 1: Record your intent parameters before submission. Before initiating any cross-chain swap, document the following: the source token and amount, the destination token and expected amount, the source and destination chain IDs, the slippage tolerance you selected, and the deadline you set. Screenshot the swap confirmation screen showing these parameters. This is your baseline for verification — without it, you cannot prove what you intended versus what was executed.

Step 2: Capture the intent transaction hash. When you submit your intent, the transaction is recorded on-chain. Copy the transaction hash from your wallet’s activity feed or the swap interface. Do not rely on the swap provider’s transaction history, which could be manipulated. Verify the transaction hash independently on the source chain’s block explorer by searching your wallet address.

Step 3: Decode the intent calldata. Using your calldata decoder, examine the input data of your intent transaction. Verify that the parameters encoded in the calldata match the parameters you recorded in Step 1. Pay particular attention to the destination address — this is where a malicious dApp or compromised frontend could redirect your funds. If the destination address in the calldata does not match your actual wallet address, the swap was set up to steal your funds, and you should investigate immediately.

Step 4: Monitor solver execution. Intent-based systems relay your intent to a network of solvers who compete to fulfill it. The winning solver submits a transaction on the destination chain that delivers your tokens. Find this transaction by searching your destination wallet address on the destination chain’s block explorer, filtering for incoming token transfers around the time of your intent submission. Cross-reference the transaction’s from address against known solver addresses published by the protocol.

Step 5: Verify the received amount against expected output. Compare the actual token amount received on the destination chain against the expected amount from Step 1, accounting for your slippage tolerance. If the received amount is below your minimum acceptable output (expected amount minus slippage), the solver may have exploited the swap for additional profit. Document the discrepancy and report it to the protocol’s support channels with transaction evidence.

Step 6: Audit token approvals generated by the swap. Cross-chain swaps typically require you to approve the swap contract to spend your tokens. After the swap completes, check your token approvals on the source chain using Etherscan’s token approval checker or Revoke.cash. Verify that only the expected approval was created and that the approved amount is not set to the maximum uint256 value unless you explicitly chose unlimited approval. Revoke any unnecessary approvals immediately after the swap completes.

Troubleshooting

Transaction not appearing on destination chain: Cross-chain swaps can take anywhere from seconds to hours depending on the chains involved and network congestion. First, verify that the intent transaction on the source chain was confirmed (status: success). Then check if the solver transaction is pending in the destination chain’s mempool. If more than 30 minutes have passed with no activity on the destination chain, the swap may have failed and your funds should be returned to the source chain automatically. Check your source wallet for a refund transaction.

Received fewer tokens than expected: Beyond normal slippage, unexpected shortfalls can indicate solver manipulation or MEV extraction on the destination chain. If the shortfall exceeds your slippage tolerance, gather transaction evidence from both chains and file a support ticket with the protocol. Some intent-based systems offer solver slashing mechanisms that can compensate users for verified manipulation.

Unknown token approval appeared: If you find an approval for a contract address you do not recognize, do not panic — cross-chain swap contracts may use intermediate contracts that are not immediately recognizable. Cross-reference the approved contract address against the protocol’s documentation. If the address is not listed as an official contract, revoke the approval immediately and investigate whether you interacted with a phishing interface.

Mastering the Skill

Advanced swap verification becomes second nature with practice. Start by verifying every cross-chain swap you execute using the steps above, even small test transactions. As you build familiarity with the calldata patterns of your preferred protocols, you will develop an intuitive sense for what normal execution looks like — and more importantly, what abnormal execution looks like. Set up automated monitoring using tools like Tenderly alerts, which can notify you whenever a transaction involving your addresses deviates from expected patterns. For AI agent operators, implement these verification checks programmatically in your agent’s execution pipeline to catch manipulation in real-time. The one-million-swap milestone on NEAR Intents means the cross-chain economy is scaling rapidly — ensure your verification skills keep pace.

Disclaimer: This tutorial is for educational purposes only and does not constitute financial or security advice. Always verify contract addresses through official documentation and test with small amounts before executing large cross-chain transactions.