MCP Ethers Wallet

Instructions

Implementation Reference

• src/tools/core.ts:1171-1261 (registration)

  Registration of the 'prepareContractTransaction' MCP tool, including input schema and the handler function that prepares the contract transaction using ethersService and returns formatted response.

    // Prepare Contract Transaction tool
    server.tool(
      "prepareContractTransaction", 
      "Prepare a smart contract interaction transaction for signing. Returns transaction data that can be signed and broadcast.",
      {
        contractAddress: z.string().regex(/^0x[a-fA-F0-9]{40}$/).describe(
          "The smart contract address to interact with"
        ),
        data: z.string().regex(/^0x[a-fA-F0-9]*$/).describe(
          "The contract interaction data (encoded function call) as hex string"
        ),
        value: z.string().optional().default("0").describe(
          "Optional. The amount of ETH to send with the transaction (default: '0')"
        ),
        fromAddress: z.string().regex(/^0x[a-fA-F0-9]{40}$/).describe(
          "The Ethereum address sending the transaction"
        ),
        provider: z.string().optional().describe(PROVIDER_DESCRIPTION),
        chainId: z.number().optional().describe(
          "Optional. The chain ID to use."
        ),
        gasLimit: z.string().optional().describe(
          "Optional. The gas limit for the transaction"
        ),
        gasPrice: z.string().optional().describe(
          "Optional. The gas price (in gwei) for legacy transactions"
        ),
        maxFeePerGas: z.string().optional().describe(
          "Optional. The maximum fee per gas (in gwei) for EIP-1559 transactions"
        ),
        maxPriorityFeePerGas: z.string().optional().describe(
          "Optional. The maximum priority fee per gas (in gwei) for EIP-1559 transactions"
        )
      },
      async ({ contractAddress, data, value, fromAddress, provider, chainId, gasLimit, gasPrice, maxFeePerGas, maxPriorityFeePerGas }) => {
        try {
          // Prepare gas options
          const options = {
            gasLimit,
            gasPrice,
            maxFeePerGas,
            maxPriorityFeePerGas
          };
          
          const txRequest = await ethersService.prepareContractTransaction(
            contractAddress,
            data,
            value || "0",
            fromAddress,
            provider,
            chainId,
            options
          );
          
          return {
            content: [{ 
              type: "text", 
              text: `Contract Transaction Prepared:
  
  Contract: ${contractAddress}
  From: ${fromAddress}
  Value: ${value || "0"} ETH
  Data: ${data}
  
  Transaction Data:
  ${JSON.stringify({
    to: txRequest.to,
    data: txRequest.data,
    value: txRequest.value?.toString(),
    from: txRequest.from,
    gasLimit: txRequest.gasLimit?.toString(),
    gasPrice: txRequest.gasPrice?.toString(),
    maxFeePerGas: txRequest.maxFeePerGas?.toString(),
    maxPriorityFeePerGas: txRequest.maxPriorityFeePerGas?.toString(),
    chainId: txRequest.chainId
  }, null, 2)}
  
  This transaction is ready to be signed and broadcast.`
            }]
          };
        } catch (error) {
          return {
            isError: true,
            content: [{ 
              type: "text", 
              text: `Error preparing contract transaction: ${error instanceof Error ? error.message : String(error)}`
            }]
          };
        }
      }
    );

• src/tools/core.ts:1205-1260 (handler)

  The MCP tool handler function for 'prepareContractTransaction' that validates inputs, calls ethersService helper, formats the transaction data, and returns a text response.

      async ({ contractAddress, data, value, fromAddress, provider, chainId, gasLimit, gasPrice, maxFeePerGas, maxPriorityFeePerGas }) => {
        try {
          // Prepare gas options
          const options = {
            gasLimit,
            gasPrice,
            maxFeePerGas,
            maxPriorityFeePerGas
          };
          
          const txRequest = await ethersService.prepareContractTransaction(
            contractAddress,
            data,
            value || "0",
            fromAddress,
            provider,
            chainId,
            options
          );
          
          return {
            content: [{ 
              type: "text", 
              text: `Contract Transaction Prepared:
  
  Contract: ${contractAddress}
  From: ${fromAddress}
  Value: ${value || "0"} ETH
  Data: ${data}
  
  Transaction Data:
  ${JSON.stringify({
    to: txRequest.to,
    data: txRequest.data,
    value: txRequest.value?.toString(),
    from: txRequest.from,
    gasLimit: txRequest.gasLimit?.toString(),
    gasPrice: txRequest.gasPrice?.toString(),
    maxFeePerGas: txRequest.maxFeePerGas?.toString(),
    maxPriorityFeePerGas: txRequest.maxPriorityFeePerGas?.toString(),
    chainId: txRequest.chainId
  }, null, 2)}
  
  This transaction is ready to be signed and broadcast.`
            }]
          };
        } catch (error) {
          return {
            isError: true,
            content: [{ 
              type: "text", 
              text: `Error preparing contract transaction: ${error instanceof Error ? error.message : String(error)}`
            }]
          };
        }
      }

• src/tools/core.ts:1175-1204 (schema)

  Zod schema for input parameters of the 'prepareContractTransaction' tool.

  {
    contractAddress: z.string().regex(/^0x[a-fA-F0-9]{40}$/).describe(
      "The smart contract address to interact with"
    ),
    data: z.string().regex(/^0x[a-fA-F0-9]*$/).describe(
      "The contract interaction data (encoded function call) as hex string"
    ),
    value: z.string().optional().default("0").describe(
      "Optional. The amount of ETH to send with the transaction (default: '0')"
    ),
    fromAddress: z.string().regex(/^0x[a-fA-F0-9]{40}$/).describe(
      "The Ethereum address sending the transaction"
    ),
    provider: z.string().optional().describe(PROVIDER_DESCRIPTION),
    chainId: z.number().optional().describe(
      "Optional. The chain ID to use."
    ),
    gasLimit: z.string().optional().describe(
      "Optional. The gas limit for the transaction"
    ),
    gasPrice: z.string().optional().describe(
      "Optional. The gas price (in gwei) for legacy transactions"
    ),
    maxFeePerGas: z.string().optional().describe(
      "Optional. The maximum fee per gas (in gwei) for EIP-1559 transactions"
    ),
    maxPriorityFeePerGas: z.string().optional().describe(
      "Optional. The maximum priority fee per gas (in gwei) for EIP-1559 transactions"
    )
  },