skill-02-smart-contract-interaction

Smart Contract Interaction

When to Use

• Reading contract state (view/pure functions)
• Writing transactions (state-changing calls)
• Encoding/decoding ABI data
• Deploying contracts (direct or via factory)
• Working with proxy patterns (EIP-1967, UUPS, Transparent)
• Batching reads with Multicall3

Prerequisites

• MCP: blockchain-rpc-server
• MCP: defi-protocol-server for known protocol ABIs
• MCP: security-audit screening for unknown contracts
• Guardrails: verify contract before interaction

Workflow

1. Contract Verification

Before any write interaction:

1. Check contract is verified on block explorer (Etherscan API)
2. Compare bytecode hash if unverified — block if mismatch with known good
3. Run rug-pull pattern checks (see skill-08)
4. Confirm address is not on sanctions list

2. Read Calls

// Prefer eth_call with explicit block tag
const result = await provider.call({
  to: contractAddress,
  data: iface.encodeFunctionData('balanceOf', [userAddress])
}, 'latest');

Use Multicall3 (0xcA11bde05977b3631167028862bE2a173976CA11) to batch reads.

3. Write Calls

1. Encode function call with ABI
2. Estimate gas: eth_estimateGas + 20% buffer
3. Simulate via eth_call with from set to signer
4. Check token approvals — warn if type(uint256).max
5. Submit transaction with appropriate gas params (see skill-12)

4. Deployment

Pattern	When to Use
Direct deploy	Simple, immutable contracts
CREATE2	Deterministic addresses across chains
EIP-1967 Proxy	Upgradeable logic contracts
UUPS	Gas-efficient upgrades (logic owns upgrade)
Minimal Proxy (EIP-1167)	Clone factory patterns

5. Proxy Interaction

• Read implementation: storage slot 0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc
• Always interact with proxy address, not implementation
• Verify implementation is not self-destructable without timelock

ABI Resources

• knowledge-base/standards/ — ERC interface ABIs
• defi-protocol-server — Pre-indexed protocol ABIs
• Etherscan verified source for unknown contracts

References

• references/multicall-patterns.md
• references/proxy-patterns.md